1
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Sinha AK, Laursen MF, Brinck JE, Rybtke ML, Hjørne AP, Procházková N, Pedersen M, Roager HM, Licht TR. Dietary fibre directs microbial tryptophan metabolism via metabolic interactions in the gut microbiota. Nat Microbiol 2024; 9:1964-1978. [PMID: 38918470 PMCID: PMC11306097 DOI: 10.1038/s41564-024-01737-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2023] [Accepted: 05/17/2024] [Indexed: 06/27/2024]
Abstract
Tryptophan is catabolized by gut microorganisms resulting in a wide range of metabolites implicated in both beneficial and adverse host effects. How gut microbial tryptophan metabolism is directed towards indole, associated with chronic kidney disease, or towards protective indolelactic acid (ILA) and indolepropionic acid (IPA) is unclear. Here we used in vitro culturing and animal experiments to assess gut microbial competition for tryptophan and the resulting metabolites in a controlled three-species defined community and in complex undefined human faecal communities. The generation of specific tryptophan-derived metabolites was not predominantly determined by the abundance of tryptophan-metabolizing bacteria, but rather by substrate-dependent regulation of specific metabolic pathways. Indole-producing Escherichia coli and ILA- and IPA-producing Clostridium sporogenes competed for tryptophan within the three-species community in vitro and in vivo. Importantly, fibre-degrading Bacteroides thetaiotaomicron affected this competition by cross-feeding monosaccharides to E. coli. This inhibited indole production through catabolite repression, thus making more tryptophan available to C. sporogenes, resulting in increased ILA and IPA production. The fibre-dependent reduction in indole was confirmed using human faecal cultures and faecal-microbiota-transplanted gnotobiotic mice. Our findings explain why consumption of fermentable fibres suppresses indole production but promotes the generation of other tryptophan metabolites associated with health benefits.
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Affiliation(s)
- Anurag K Sinha
- National Food Institute, Technical University of Denmark, Kongens Lyngby, Denmark.
| | - Martin F Laursen
- National Food Institute, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Julius E Brinck
- National Food Institute, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Morten L Rybtke
- National Food Institute, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Anna Pii Hjørne
- National Food Institute, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Nicola Procházková
- Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Mikael Pedersen
- National Food Institute, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Henrik M Roager
- Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Tine R Licht
- National Food Institute, Technical University of Denmark, Kongens Lyngby, Denmark.
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2
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Judd HNG, Martínez AK, Klepacki D, Vázquez-Laslop N, Sachs MS, Cruz-Vera LR. Functional domains of a ribosome arresting peptide are affected by surrounding nonconserved residues. J Biol Chem 2024; 300:105780. [PMID: 38395310 PMCID: PMC10941005 DOI: 10.1016/j.jbc.2024.105780] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2023] [Revised: 02/12/2024] [Accepted: 02/15/2024] [Indexed: 02/25/2024] Open
Abstract
Expression of the Escherichia coli tnaCAB operon, responsible for L-tryptophan (L-Trp) transport and catabolism, is regulated by L-Trp-directed translation arrest and the ribosome arresting peptide TnaC. The function of TnaC relies on conserved residues distributed throughout the peptide, which are involved in forming an L-Trp binding site at the ribosome exit tunnel and inhibiting the ribosome function. We aimed to understand whether nonconserved amino acids surrounding these critical conserved residues play a functional role in TnaC-mediated ribosome arrest. We have isolated two intragenic suppressor mutations that restore arrest function of TnaC mutants; one of these mutations is located near the L-Trp binding site, while the other mutation is located near the ribosome active site. We used reporter gene fusions to show that both suppressor mutations have similar effects on TnaC mutants at the conserved residues involved in forming a free L-Trp binding site. However, they diverge in suppressing loss-of-function mutations in a conserved TnaC residue at the ribosome active site. With ribosome toeprinting assays, we determined that both suppressor mutations generate TnaC peptides, which are highly sensitive to L-Trp. Puromycin-challenge assays with isolated arrested ribosomes indicate that both TnaC suppressor mutants are resistant to peptidyl-tRNA cleavage by puromycin in the presence of L-Trp; however, they differ in their resistance to puromycin in the absence of L-Trp. We propose that the TnaC peptide two functionally distinct segments, a sensor domain and a stalling domain, and that the functional versatility of these domains is fine-tuned by the nature of their surrounding nonconserved residues.
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Affiliation(s)
- Heather N G Judd
- Department of Biological Sciences, University of Alabama in Huntsville, Huntsville, Alabama, USA
| | - Allyson K Martínez
- Department of Biology, Texas A&M University, College Station, Texas, USA
| | - Dorota Klepacki
- Department of Pharmaceutical Sciences, University of Illinois at Chicago, Chicago, Illinois, USA; Center for Biomolecular Sciences, University of Illinois at Chicago, Chicago, Illinois, USA
| | - Nora Vázquez-Laslop
- Department of Pharmaceutical Sciences, University of Illinois at Chicago, Chicago, Illinois, USA; Center for Biomolecular Sciences, University of Illinois at Chicago, Chicago, Illinois, USA
| | - Matthew S Sachs
- Department of Biology, Texas A&M University, College Station, Texas, USA
| | - Luis R Cruz-Vera
- Department of Biological Sciences, University of Alabama in Huntsville, Huntsville, Alabama, USA.
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3
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Lang M, Krin E, Korlowski C, Sismeiro O, Varet H, Coppée JY, Mazel D, Baharoglu Z. Sleeping ribosomes: Bacterial signaling triggers RaiA mediated persistence to aminoglycosides. iScience 2021; 24:103128. [PMID: 34611612 PMCID: PMC8476650 DOI: 10.1016/j.isci.2021.103128] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Revised: 09/07/2021] [Accepted: 09/09/2021] [Indexed: 12/19/2022] Open
Abstract
Indole is a molecule proposed to be involved in bacterial signaling. We find that indole secretion is induced by sublethal tobramycin concentrations and increases persistence to aminoglycosides in V. cholerae. Indole transcriptomics showed increased expression of raiA, a ribosome associated factor. Deletion of raiA abolishes the appearance of indole dependent persisters to aminoglycosides, although its overexpression leads to 100-fold increase of persisters, and a reduction in lag phase, evocative of increased active 70S ribosome content, confirmed by sucrose gradient analysis. We propose that, under stress conditions, RaiA-bound inactive 70S ribosomes are stored as “sleeping ribosomes”, and are rapidly reactivated upon stress relief. Our results point to an active process of persister formation through ribosome protection during translational stress (e.g., aminoglycoside treatment) and reactivation upon antibiotic removal. Translation is a universal process, and these results could help elucidate a mechanism of persistence formation in a controlled, thus inducible way. Indole is produced under sub-MIC tobramycin stress in V. cholerae and upregulates raiA RaiA is involved in indole-dependent formation of aminoglycoside specific persisters RaiA overexpression allows faster growth restart and increases 70S ribosome content RaiA-bound inactive 70S ribosomes form intact and reactivable sleeping ribosome pools
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Affiliation(s)
- Manon Lang
- Département Génomes et Génétique, Institut Pasteur, UMR3525, CNRS, Unité Plasticité du Génome Bactérien, 75015 Paris, France
- Sorbonne Université, Collège Doctoral, 75005 Paris, France
| | - Evelyne Krin
- Département Génomes et Génétique, Institut Pasteur, UMR3525, CNRS, Unité Plasticité du Génome Bactérien, 75015 Paris, France
| | - Chloé Korlowski
- Département Génomes et Génétique, Institut Pasteur, UMR3525, CNRS, Unité Plasticité du Génome Bactérien, 75015 Paris, France
| | - Odile Sismeiro
- Biomics Technological Platform, Center for Technological Resources and Research, Institut Pasteur, 75015 Paris, France
| | - Hugo Varet
- Biomics Technological Platform, Center for Technological Resources and Research, Institut Pasteur, 75015 Paris, France
- Bioinformatics and Biostatistics Hub, Department of Computational Biology, USR 3756 CNRS, Institut Pasteur, 75015 Paris, France
| | - Jean-Yves Coppée
- Biomics Technological Platform, Center for Technological Resources and Research, Institut Pasteur, 75015 Paris, France
| | - Didier Mazel
- Département Génomes et Génétique, Institut Pasteur, UMR3525, CNRS, Unité Plasticité du Génome Bactérien, 75015 Paris, France
- Corresponding author
| | - Zeynep Baharoglu
- Département Génomes et Génétique, Institut Pasteur, UMR3525, CNRS, Unité Plasticité du Génome Bactérien, 75015 Paris, France
- Corresponding author
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4
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Structural basis for the tryptophan sensitivity of TnaC-mediated ribosome stalling. Nat Commun 2021; 12:5340. [PMID: 34504068 PMCID: PMC8429421 DOI: 10.1038/s41467-021-25663-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Accepted: 08/24/2021] [Indexed: 02/07/2023] Open
Abstract
Free L-tryptophan (L-Trp) stalls ribosomes engaged in the synthesis of TnaC, a leader peptide controlling the expression of the Escherichia coli tryptophanase operon. Despite extensive characterization, the molecular mechanism underlying the recognition and response to L-Trp by the TnaC-ribosome complex remains unknown. Here, we use a combined biochemical and structural approach to characterize a TnaC variant (R23F) with greatly enhanced sensitivity for L-Trp. We show that the TnaC-ribosome complex captures a single L-Trp molecule to undergo termination arrest and that nascent TnaC prevents the catalytic GGQ loop of release factor 2 from adopting an active conformation at the peptidyl transferase center. Importantly, the L-Trp binding site is not altered by the R23F mutation, suggesting that the relative rates of L-Trp binding and peptidyl-tRNA cleavage determine the tryptophan sensitivity of each variant. Thus, our study reveals a strategy whereby a nascent peptide assists the ribosome in detecting a small metabolite.
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5
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Abstract
Despite our extensive knowledge of the genetic regulation of heat shock proteins (HSPs), the evolutionary routes that allow bacteria to adaptively tune their HSP levels and corresponding proteostatic robustness have been explored less. In this report, directed evolution experiments using the Escherichia coli model system unexpectedly revealed that seemingly random single mutations in its tnaA gene can confer significant heat resistance. Closer examination, however, indicated that these mutations create folding-deficient and aggregation-prone TnaA variants that in turn can endogenously and preemptively trigger HSP expression to cause heat resistance. These findings, importantly, demonstrate that even erosive mutations with disruptive effects on protein structure and functionality can still yield true gain-of-function alleles with a selective advantage in adaptive evolution.
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6
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Sherman MW, Sandeep S, Contreras LM. The Tryptophan-Induced tnaC Ribosome Stalling Sequence Exposes High Amino Acid Cross-Talk That Can Be Mitigated by Removal of NusB for Higher Orthogonality. ACS Synth Biol 2021; 10:1024-1038. [PMID: 33835775 DOI: 10.1021/acssynbio.0c00547] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
A growing number of engineered synthetic circuits have employed biological parts coupling transcription and translation in bacterial systems to control downstream gene expression. One such example, the leader sequence of the tryptophanase (tna) operon, is a transcription-translation system commonly employed as an l-tryptophan inducible circuit controlled by ribosome stalling. While induction of the tna operon has been well-characterized in response to l-tryptophan, cross-talk of this modular component with other metabolites in the cell, such as other naturally occurring amino acids, has been less explored. In this study, we investigated the impact of natural metabolites and E. coli host factors on induction of the tna leader sequence. To do so, we constructed and biochemically validated an experimental assay using the tna operon leader sequence to assess differential regulation of transcription elongation and translation in response to l-tryptophan. Operon induction was then assessed following addition of each of the 20 naturally occurring amino acids to discover that several additional amino acids (e.g., l-alanine, l-cysteine, l-glycine, l-methionine, and l-threonine) also induce expression of the tna leader sequence. Following characterization of dose-dependent induction by l-cysteine relative to l-tryptophan, the effect on induction by single gene knockouts of protein factors associated with transcription and/or translation were interrogated. Our results implicate the endogenous cellular protein, NusB, as an important factor associated with induction of the operon by the alternative amino acids. As such, removal of the nusB gene from strains intended for tryptophan-sensing utilizing the tna leader region reduces amino acid cross-talk, resulting in enhanced orthogonal control of this commonly used synthetic system.
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Affiliation(s)
- Mark W. Sherman
- Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, Texas 78714, United States
| | - Sanjna Sandeep
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78714, United States
| | - Lydia M. Contreras
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78714, United States
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7
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Rosenberg G, Yehezkel D, Hoffman D, Mattioli CC, Fremder M, Ben-Arosh H, Vainman L, Nissani N, Hen-Avivi S, Brenner S, Itkin M, Malitsky S, Ohana E, Ben-Moshe NB, Avraham R. Host succinate is an activation signal for
Salmonella
virulence during intracellular infection. Science 2021; 371:400-405. [DOI: 10.1126/science.aba8026] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2020] [Revised: 08/06/2020] [Accepted: 11/20/2020] [Indexed: 12/11/2022]
Affiliation(s)
- Gili Rosenberg
- Department of Biological Regulation, Weizmann Institute of Science, 7610001 Rehovot, Israel
| | - Dror Yehezkel
- Department of Biological Regulation, Weizmann Institute of Science, 7610001 Rehovot, Israel
| | - Dotan Hoffman
- Department of Biological Regulation, Weizmann Institute of Science, 7610001 Rehovot, Israel
| | | | - Moran Fremder
- Department of Clinical Biochemistry and Pharmacology, Faculty of Health Sciences, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel
| | - Hadar Ben-Arosh
- Department of Biological Regulation, Weizmann Institute of Science, 7610001 Rehovot, Israel
| | - Leia Vainman
- Department of Biological Regulation, Weizmann Institute of Science, 7610001 Rehovot, Israel
| | - Noa Nissani
- Department of Biological Regulation, Weizmann Institute of Science, 7610001 Rehovot, Israel
| | - Shelly Hen-Avivi
- Department of Biological Regulation, Weizmann Institute of Science, 7610001 Rehovot, Israel
| | - Shirley Brenner
- Department of Biological Regulation, Weizmann Institute of Science, 7610001 Rehovot, Israel
| | - Maxim Itkin
- Life Sciences Core Facilities, Weizmann Institute of Science, 7610001 Rehovot, Israel
| | - Sergey Malitsky
- Life Sciences Core Facilities, Weizmann Institute of Science, 7610001 Rehovot, Israel
| | - Ehud Ohana
- Department of Clinical Biochemistry and Pharmacology, Faculty of Health Sciences, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel
| | - Noa Bossel Ben-Moshe
- Department of Biological Regulation, Weizmann Institute of Science, 7610001 Rehovot, Israel
| | - Roi Avraham
- Department of Biological Regulation, Weizmann Institute of Science, 7610001 Rehovot, Israel
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8
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Role of Gut Microbiome and Microbial Metabolites in Alleviating Insulin Resistance After Bariatric Surgery. Obes Surg 2020; 31:327-336. [PMID: 32974816 DOI: 10.1007/s11695-020-04974-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2020] [Revised: 09/05/2020] [Accepted: 09/11/2020] [Indexed: 02/07/2023]
Abstract
Insulin resistance (IR) is the most common pathophysiological change in patients with type 2 diabetes mellitus (T2DM). Several recent studies have suggested that the gut microbiome and microbial metabolites are involved in the pathogenesis of IR. Bariatric surgery, as an effective treatment for T2DM, can markedly alleviate IR through mechanisms that have not been elucidated. In this review, we summarize the current evidence on the changes in the gut microbiome and microbial metabolites (including lipopolysaccharide, short-chain fatty acids, branched-chain amino acids, aromatic amino acids, bile acids, methylamines, and indole derivatives) after bariatric surgery. Additionally, we discuss the mechanisms that correlate the changes in microbial metabolites with the postoperative alleviation of IR. Furthermore, we discuss the prospect of bariatric surgery as a treatment for T2DM.
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9
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Posttranscriptional Regulation of tnaA by Protein-RNA Interaction Mediated by Ribosomal Protein L4 in Escherichia coli. J Bacteriol 2020; 202:JB.00799-19. [PMID: 32123036 PMCID: PMC7186457 DOI: 10.1128/jb.00799-19] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2020] [Accepted: 02/13/2020] [Indexed: 11/26/2022] Open
Abstract
Some ribosomal proteins have extraribosomal functions in addition to ribosome translation function. The extraribosomal functions of several r-proteins control operon expression by binding to own-operon transcripts. Previously, we discovered a posttranscriptional, RNase E-dependent regulatory role for r-protein L4 in the stabilization of stress-responsive transcripts. Here, we found an additional extraribosomal function for L4 in regulating the tna operon by L4-intergenic spacer mRNA interactions. L4 binds to the transcribed spacer RNA between tnaC and tnaA and alters the structural conformation of the spacer RNA, thereby reducing the translation of TnaA. Our study establishes a previously unknown L4-mediated mechanism for regulating gene expression, suggesting that bacterial cells have multiple strategies for controlling levels of tryptophanase in response to varied cell growth conditions. Escherichia coli ribosomal protein (r-protein) L4 has extraribosomal biological functions. Previously, we described L4 as inhibiting RNase E activity through protein-protein interactions. Here, we report that from stabilized transcripts regulated by L4-RNase E, mRNA levels of tnaA (encoding tryptophanase from the tnaCAB operon) increased upon ectopic L4 expression, whereas TnaA protein levels decreased. However, at nonpermissive temperatures (to inactivate RNase E), tnaA mRNA and protein levels both increased in an rne temperature-sensitive [rne(Ts)] mutant strain. Thus, L4 protein fine-tunes TnaA protein levels independently of its inhibition of RNase E. We demonstrate that ectopically expressed L4 binds with transcribed spacer RNA between tnaC and tnaA and downregulates TnaA translation. We found that deletion of the 5′ or 3′ half of the spacer compared to the wild type resulted in a similar reduction in TnaA translation in the presence of L4. In vitro binding of L4 to the tnaC-tnaA transcribed spacer RNA results in changes to its secondary structure. We reveal that during early stationary-phase bacterial growth, steady-state levels of tnaA mRNA increased but TnaA protein levels decreased. We further confirm that endogenous L4 binds to tnaC-tnaA transcribed spacer RNA in cells at early stationary phase. Our results reveal the novel function of L4 in fine-tuning TnaA protein levels during cell growth and demonstrate that r-protein L4 acts as a translation regulator outside the ribosome and its own operon. IMPORTANCE Some ribosomal proteins have extraribosomal functions in addition to ribosome translation function. The extraribosomal functions of several r-proteins control operon expression by binding to own-operon transcripts. Previously, we discovered a posttranscriptional, RNase E-dependent regulatory role for r-protein L4 in the stabilization of stress-responsive transcripts. Here, we found an additional extraribosomal function for L4 in regulating the tna operon by L4-intergenic spacer mRNA interactions. L4 binds to the transcribed spacer RNA between tnaC and tnaA and alters the structural conformation of the spacer RNA, thereby reducing the translation of TnaA. Our study establishes a previously unknown L4-mediated mechanism for regulating gene expression, suggesting that bacterial cells have multiple strategies for controlling levels of tryptophanase in response to varied cell growth conditions.
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10
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Metabolic output defines Escherichia coli as a health-promoting microbe against intestinal Pseudomonas aeruginosa. Sci Rep 2019; 9:14463. [PMID: 31595010 PMCID: PMC6783455 DOI: 10.1038/s41598-019-51058-3] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2019] [Accepted: 09/25/2019] [Indexed: 12/15/2022] Open
Abstract
Gut microbiota acts as a barrier against intestinal pathogens, but species-specific protection of the host from infection remains relatively unexplored. Although lactobacilli and bifidobacteria produce beneficial lactic and short-chain fatty acids in the mammalian gut, the significance of intestinal Escherichia coli producing these acids is debatable. Taking a Koch’s postulates approach in reverse, we define Escherichia coli as health-promoting for naturally colonizing the gut of healthy mice and protecting them against intestinal colonization and concomitant mortality by Pseudomonas aeruginosa. Reintroduction of faecal bacteria and E. coli in antibiotic-treated mice establishes a high titre of E. coli in the host intestine and increases defence against P. aeruginosa colonization and mortality. Strikingly, high sugar concentration favours E. coli fermentation to lactic and acetic acid and inhibits P. aeruginosa growth and virulence in aerobic cultures and in a model of aerobic metabolism in flies, while dietary vegetable fats - not carbohydrates or proteins - favour E. coli fermentation and protect the host in the anaerobic mouse gut. Thus E. coli metabolic output is an important indicator of resistance to infection. Our work may also suggest that the lack of antimicrobial bacterial metabolites in mammalian lungs and wounds allows P. aeruginosa to be a formidable microbe at these sites.
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11
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Correlation of tryptophan metabolites with connectivity of extended central reward network in healthy subjects. PLoS One 2018; 13:e0201772. [PMID: 30080865 PMCID: PMC6078307 DOI: 10.1371/journal.pone.0201772] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Accepted: 07/20/2018] [Indexed: 01/16/2023] Open
Abstract
OBJECTIVE A growing body of preclinical and clinical literature suggests that brain-gut-microbiota interactions play an important role in human health and disease, including hedonic food intake and obesity. We performed a tripartite network analysis based on graph theory to test the hypothesis that microbiota-derived fecal metabolites are associated with connectivity of key regions of the brain's extended reward network and clinical measures related to obesity. METHODS DTI and resting state fMRI imaging was obtained from 63 healthy subjects with and without elevated body mass index (BMI) (29 males and 34 females). Subjects submitted fecal samples, completed questionnaires to assess anxiety and food addiction, and BMI was recorded. RESULTS The study results demonstrate associations between fecal microbiota-derived indole metabolites (indole, indoleacetic acid, and skatole) with measures of functional and anatomical connectivity of the amygdala, nucleus accumbens, and anterior insula, in addition to BMI, food addiction scores (YFAS) and anxiety symptom scores (HAD Anxiety). CONCLUSIONS The findings support the hypothesis that gut microbiota-derived indole metabolites may influence hedonic food intake and obesity by acting on the extended reward network, specifically the amygdala-nucleus accumbens circuit and the amygdala-anterior insula circuit. These cross sectional, data-driven results provide valuable information for future mechanistic studies.
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12
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Hsu TM, Welner DH, Russ ZN, Cervantes B, Prathuri RL, Adams PD, Dueber JE. Employing a biochemical protecting group for a sustainable indigo dyeing strategy. Nat Chem Biol 2018; 14:256-261. [PMID: 29309053 PMCID: PMC5866135 DOI: 10.1038/nchembio.2552] [Citation(s) in RCA: 85] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Accepted: 11/14/2017] [Indexed: 11/09/2022]
Abstract
Indigo is an ancient dye uniquely capable of producing the signature tones in blue denim; however, the dyeing process requires chemical steps that are environmentally damaging. We describe a sustainable dyeing strategy that not only circumvents the use of toxic reagents for indigo chemical synthesis but also removes the need for a reducing agent for dye solubilization. This strategy utilizes a glucose moiety as a biochemical protecting group to stabilize the reactive indigo precursor indoxyl to form indican, preventing spontaneous oxidation to crystalline indigo during microbial fermentation. Application of a β-glucosidase removes the protecting group from indican, resulting in indigo crystal formation in the cotton fibers. We identified the gene coding for the glucosyltransferase PtUGT1 from the indigo plant Polygonum tinctorium and solved the structure of PtUGT1. Heterologous expression of PtUGT1 in Escherichia coli supported high indican conversion, and biosynthesized indican was used to dye cotton swatches and a garment.
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Affiliation(s)
- Tammy M Hsu
- Department of Bioengineering, University of California, Berkeley, Berkeley, California, USA
- UC Berkeley-UCSF Graduate Program in Bioengineering, University of California, Berkeley, Berkeley, California, USA
| | - Ditte H Welner
- Joint BioEnergy Institute, Emeryville, California, USA
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratories, Berkeley, California, USA
| | - Zachary N Russ
- Department of Bioengineering, University of California, Berkeley, Berkeley, California, USA
- UC Berkeley-UCSF Graduate Program in Bioengineering, University of California, Berkeley, Berkeley, California, USA
| | - Bernardo Cervantes
- Department of Bioengineering, University of California, Berkeley, Berkeley, California, USA
| | - Ramya L Prathuri
- Department of Bioengineering, University of California, Berkeley, Berkeley, California, USA
| | - Paul D Adams
- Department of Bioengineering, University of California, Berkeley, Berkeley, California, USA
- Joint BioEnergy Institute, Emeryville, California, USA
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratories, Berkeley, California, USA
| | - John E Dueber
- Department of Bioengineering, University of California, Berkeley, Berkeley, California, USA
- Biological Systems & Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
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13
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Zhang S, Zhang W, Liu N, Song T, Liu H, Zhao X, Xu W, Li C. Indole reduces the expression of virulence related genes in Vibrio splendidus pathogenic to sea cucumber Apostichopus japonicus. Microb Pathog 2017; 111:168-173. [PMID: 28867630 DOI: 10.1016/j.micpath.2017.08.032] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Revised: 08/06/2017] [Accepted: 08/30/2017] [Indexed: 12/24/2022]
Abstract
Indole is a metabolite of tryptophan that can be synthesized by various bacteria. In the present study, production of indole by Vibrio splendidus Vs was determined using Kovac's reagent, and m/z was further determined by HPLC-MS. Extracellular indole reached a maximum concentration of 160 μM, when OD600 of V. splendidus Vs was approximately 0.9. In addition, glucose could reduce indole level, and 1% (m/v) glucose could reduce the mRNA level of tnaA, the gene encoding tryptophanase, down to 0.2%. To investigate the effects of indole on the mRNA levels of virulence related genes of V. splendidus Vs, mRNA levels of vsm, vsh and ABC respectively related to protease activity, haemolytic activity and ABC transporter ATP-binding protein were determined. Exogenous indole supplemented at a concentration of 125 μΜ could respectively down regulate the mRNA level of vsm, vsh and ABC to 16%, 13% and 11%. Meanwhile, indole could alter the expressions of immune related gene in Apostichopus japonicus. When coelomocytes were co-cultured with exogenous indole at a concentration of 125 μΜ, the mRNA level of Ajp105 and AjLBP/BPI1, were up regulated by 1.6-fold and 2.1-fold, respectively. Combined all the results in our study suggested that indole could alter the expressions of the virulence related genes in pathogenic V. splendidus Vs as well as the immune related genes in A. japonicus.
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Affiliation(s)
- Shanshan Zhang
- School of Marine Sciences, Ningbo University, Ningbo 315211, PR China
| | - Weiwei Zhang
- School of Marine Sciences, Ningbo University, Ningbo 315211, PR China
| | - Ningning Liu
- School of Marine Sciences, Ningbo University, Ningbo 315211, PR China
| | - Tongxiang Song
- School of Marine Sciences, Ningbo University, Ningbo 315211, PR China
| | - Huijie Liu
- School of Marine Sciences, Ningbo University, Ningbo 315211, PR China
| | - Xuelin Zhao
- School of Marine Sciences, Ningbo University, Ningbo 315211, PR China
| | - Wei Xu
- Louisiana State University, Agricultural Center, USA
| | - Chenghua Li
- School of Marine Sciences, Ningbo University, Ningbo 315211, PR China; Louisiana State University, Agricultural Center, USA.
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Panichkin VB, Livshits VA, Biryukova IV, Mashko SV. Metabolic engineering of Escherichia coli for L-tryptophan production. APPL BIOCHEM MICRO+ 2017. [DOI: 10.1134/s0003683816090052] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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15
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Zhu Y, Hua Y, Zhang B, Sun L, Li W, Kong X, Hong J. Metabolic engineering of indole pyruvic acid biosynthesis in Escherichia coli with tdiD. Microb Cell Fact 2017; 16:2. [PMID: 28049530 PMCID: PMC5209907 DOI: 10.1186/s12934-016-0620-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2016] [Accepted: 12/20/2016] [Indexed: 12/05/2022] Open
Abstract
Background Indole pyruvic acid (IPA) is a versatile platform intermediate and building block for a number of high-value products in the pharmaceutical and food industries. It also has a wide range of applications, such as drugs for the nervous system, cosmetics, and luminophores. Chemical synthesis of IPA is a complicated and costly process. Moreover, through the biosynthesis route employing l-amino acid oxidase, the byproduct hydrogen peroxide leads the degradation of IPA. TdiD, identified as a specific tryptophan aminotransferase, could be an alternative solution for efficient IPA biosynthesis. Results Escherichia coli strain W3110, which demonstrates basic production when supplied with tryptophan, was engineered for IPA biosynthesis. Several strategies were implemented to improve IPA production. First, through incorporating the codon-optimized tdiD into W3110, IPA levels increased from 41.54 ± 1.26 to 52.54 ± 2.08 mg/L. Second, after verifying the benefit of an increased phenylpyruvate pool, a YL03 strain was constructed based on a previously reported mutant strain of W3110 with a plasmid carrying aroFfbr and pheAfbr to further improve IPA production. The recombinant YL03 strain accumulated IPA at 158.85 ± 5.36 mg/L, which was 3.82-fold higher than that of the wild-type W3110 strain. Third, optimization of tdiDco expression was carried out by replacing the Trc promoter with a series of constitutively active promoters along with increasing the plasmid copy numbers. The highest IPA production was observed in YL08, which achieved 236.42 ± 17.66 mg/L and represented a greater than 5-fold increase as compared to W3110. Finally, the effects of deletion and overexpression of tnaA on IPA biosynthesis were evaluated. The removal of tnaA led to slightly reduced IPA levels, whereas the overexpression of tnaA resulted in a considerable decline in production. Conclusions This study illustrates the feasibility of IPA biosynthesis in E. coli through tdiD. An efficient IPA producing strain, YL08, was developed, which provides a new possibility for biosynthesis of IPA. Although the final production was limited, this study demonstrates a convenient method of IPA synthesis. Electronic supplementary material The online version of this article (doi:10.1186/s12934-016-0620-6) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Yelin Zhu
- School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230027, People's Republic of China
| | - Yan Hua
- School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230027, People's Republic of China
| | - Biao Zhang
- School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230027, People's Republic of China
| | - Lianhong Sun
- School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230027, People's Republic of China
| | - Wenjie Li
- School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230027, People's Republic of China
| | - Xin Kong
- School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230027, People's Republic of China
| | - Jiong Hong
- School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230027, People's Republic of China.
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Ellis RJ, Small DM, Vesey DA, Johnson DW, Francis R, Vitetta L, Gobe GC, Morais C. Indoxyl sulphate and kidney disease: Causes, consequences and interventions. Nephrology (Carlton) 2016; 21:170-7. [PMID: 26239363 DOI: 10.1111/nep.12580] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/30/2015] [Indexed: 12/28/2022]
Abstract
In the last decade, chronic kidney disease (CKD), defined as reduced renal function (glomerular filtration rate (GFR) < 60 mL/min per 1.73 m(2) ) and/or evidence of kidney damage (typically manifested as albuminuria) for at least 3 months, has become one of the fastest-growing public health concerns worldwide. CKD is characterized by reduced clearance and increased serum accumulation of metabolic waste products (uremic retention solutes). At least 152 uremic retention solutes have been reported. This review focuses on indoxyl sulphate (IS), a protein-bound, tryptophan-derived metabolite that is generated by intestinal micro-organisms (microbiota). Animal studies have demonstrated an association between IS accumulation and increased fibrosis, and oxidative stress. This has been mirrored by in vitro studies, many of which report cytotoxic effects in kidney proximal tubular cells following IS exposure. Clinical studies have associated IS accumulation with deleterious effects, such as kidney functional decline and adverse cardiovascular events, although causality has not been conclusively established. The aims of this review are to: (i) establish factors associated with increased serum accumulation of IS; (ii) report effects of IS accumulation in clinical studies; (iii) critique the reported effects of IS in the kidney, when administered both in vivo and in vitro; and (iv) summarize both established and hypothetical therapeutic options for reducing serum IS or antagonizing its reported downstream effects in the kidney.
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Affiliation(s)
- Robert J Ellis
- Centre for Kidney Disease Research, Translational Research Institute, School of Medicine, University of Queensland, Brisbane, Queensland, Australia
| | - David M Small
- Centre for Kidney Disease Research, Translational Research Institute, School of Medicine, University of Queensland, Brisbane, Queensland, Australia
| | - David A Vesey
- Centre for Kidney Disease Research, Translational Research Institute, School of Medicine, University of Queensland, Brisbane, Queensland, Australia.,Department of Renal Medicine, University of Queensland at Princess Alexandra Hospital, Brisbane, Queensland, Australia
| | - David W Johnson
- Centre for Kidney Disease Research, Translational Research Institute, School of Medicine, University of Queensland, Brisbane, Queensland, Australia.,Department of Renal Medicine, University of Queensland at Princess Alexandra Hospital, Brisbane, Queensland, Australia
| | - Ross Francis
- Department of Renal Medicine, University of Queensland at Princess Alexandra Hospital, Brisbane, Queensland, Australia
| | - Luis Vitetta
- Sydney Medical School - Medical Sciences, Medlab, Sydney, New South Wales, Australia.,Medlab Clinical Ltd., Medlab, Sydney, New South Wales, Australia
| | - Glenda C Gobe
- Centre for Kidney Disease Research, Translational Research Institute, School of Medicine, University of Queensland, Brisbane, Queensland, Australia
| | - Christudas Morais
- Centre for Kidney Disease Research, Translational Research Institute, School of Medicine, University of Queensland, Brisbane, Queensland, Australia
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Nuidate T, Tansila N, Saengkerdsub S, Kongreung J, Bakkiyaraj D, Vuddhakul V. Role of Indole Production on Virulence of Vibrio cholerae Using Galleria mellonella Larvae Model. Indian J Microbiol 2016; 56:368-74. [PMID: 27407302 DOI: 10.1007/s12088-016-0592-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2016] [Accepted: 04/29/2016] [Indexed: 12/21/2022] Open
Abstract
Cell to cell communication facilitated by chemical signals plays crucial roles in regulating various cellular functions in bacteria. Indole, one such signaling molecule has been demonstrated to control various bacterial phenotypes such as biofilm formation and virulence in diverse bacteria including Vibrio cholerae. The present study explores some key factors involved in indole production and the subsequent pathogenesis of V. cholerae. Indole production was higher at 37 °C than at 30 °C, although the growth at 37 °C was slightly higher. A positive correlation was observed between indole production and biofilm formation in V. cholerae. Maximum indole production was detected at pH 7. There was no significant difference in indole production between clinical and environmental V. cholerae isolates, although indole production in one environmental isolate was significantly different. Both growth and indole production showed relevant changes with differences in salinity. An indole negative mutant strain was constructed using transposon mutagenesis and the direct effect of indole on the virulence of V. cholerae was evaluated using Galleria mellonella larvae model. Comparison to the wild type strain, the mutant significantly reduced the mortality of G. mellonella larvae which regained its virulence after complementation with exogenous indole. A gene involved in indole production and the virulence of V. cholerae was identified.
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Affiliation(s)
- Taiyeebah Nuidate
- Food Safety and Health Research Unit, Department of Microbiology, Faculty of Science, Prince of Songkla University, Hat Yai, 90110 Thailand
| | - Natta Tansila
- Faculty of Medical Technology, Prince of Songkla University, Hat Yai, 90110 Thailand
| | - Suwat Saengkerdsub
- Department of Food Technology, Faculty of Agroindustry, Prince of Songkla University, Hat Yai, 90110 Thailand
| | - Jetnaphang Kongreung
- Food Safety and Health Research Unit, Department of Microbiology, Faculty of Science, Prince of Songkla University, Hat Yai, 90110 Thailand
| | - Dhamodharan Bakkiyaraj
- Food Safety and Health Research Unit, Department of Microbiology, Faculty of Science, Prince of Songkla University, Hat Yai, 90110 Thailand
| | - Varaporn Vuddhakul
- Food Safety and Health Research Unit, Department of Microbiology, Faculty of Science, Prince of Songkla University, Hat Yai, 90110 Thailand
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18
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Lee JH, Wood TK, Lee J. Roles of Indole as an Interspecies and Interkingdom Signaling Molecule. Trends Microbiol 2015; 23:707-718. [DOI: 10.1016/j.tim.2015.08.001] [Citation(s) in RCA: 238] [Impact Index Per Article: 26.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Revised: 07/22/2015] [Accepted: 08/05/2015] [Indexed: 02/08/2023]
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Gaimster H, Summers D. Regulation of Indole Signalling during the Transition of E. coli from Exponential to Stationary Phase. PLoS One 2015; 10:e0136691. [PMID: 26332864 PMCID: PMC4557909 DOI: 10.1371/journal.pone.0136691] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2015] [Accepted: 08/06/2015] [Indexed: 11/18/2022] Open
Abstract
During the transition from exponential to stationary phase E. coli produces a substantial quantity of the small, aromatic signalling molecule indole. In LB medium the supernatant indole concentration reaches a maximum of 0.5-1 mM. At this concentration indole has been implicated in many processes inducing acid resistance and the modulation of virulence. It has recently been shown that cell-associated indole transiently reaches a very high concentration (approx. 60 mM) during stationary phase entry, presumably because indole is being produced more rapidly than it can leave the cell. It is proposed that this indole pulse inhibits growth and cell division, causing the culture to enter stationary phase before nutrients are completely exhausted, with benefits for survival in long-term stationary phase. This study asks how E. coli cells rapidly upregulate indole production during stationary phase entry and why the indole pulse has a duration of only 10-15 min. We find that at the start of the pulse tryptophanase synthesis is triggered by glucose depletion and that this is correlates with the up-regulation of indole synthesis. The magnitude and duration of the resulting indole pulse are dependent upon the availability of exogenous tryptophan. Indole production stops when all the available tryptophan is depleted and the cell-associated indole equilibrates with the supernatant.
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Affiliation(s)
- Hannah Gaimster
- Department of Genetics, University of Cambridge, Downing Street, Cambridge, CB2 3EH, United Kingdom
- * E-mail:
| | - David Summers
- Department of Genetics, University of Cambridge, Downing Street, Cambridge, CB2 3EH, United Kingdom
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20
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Indole: a signaling molecule or a mere metabolic byproduct that alters bacterial physiology at a high concentration? J Microbiol 2015; 53:421-8. [PMID: 26115989 DOI: 10.1007/s12275-015-5273-3] [Citation(s) in RCA: 82] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2015] [Revised: 06/17/2015] [Accepted: 06/18/2015] [Indexed: 10/23/2022]
Abstract
Indole is an organic compound that is widespread in microbial communities inhabiting diverse habitats, like the soil environment and human intestines. Measurement of indole production is a traditional method for the identification of microbial species. Escherichia coli can produce millimolar concentrations of indole in the stationary growth phase under nutrient-rich conditions. Indole has received considerable attention because of its remarkable effects on various biological functions of the microbial communities, for example, biofilm formation, motility, virulence, plasmid stability, and antibiotic resistance. Indole may function as an intercellular signaling molecule, like a quorum-sensing signal. Nevertheless, a receptor system for indole and the function of this compound in coordinated behavior of a microbial population (which are requirements for a true signaling molecule) have not yet been confirmed. Recent findings suggest that a long-known quorum-sensing regulator, E. coli's SdiA, cannot recognize indole and that this compound may simply cause membrane disruption and energy reduction, which can lead to various changes in bacterial physiology including unstable folding of a quorum-sensing regulator. Indole appears to be responsible for acquisition of antibiotic resistance via the formation of persister cells and activation of an exporter. This review highlights and summarizes the current knowledge about indole as a multitrophic molecule among bacteria, together with recently identified new avenues of research.
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21
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Li G, Young KD. A cAMP-independent carbohydrate-driven mechanism inhibits tnaA expression and TnaA enzyme activity in Escherichia coli. MICROBIOLOGY-SGM 2014; 160:2079-2088. [PMID: 25061041 DOI: 10.1099/mic.0.080705-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
When Escherichia coli is grown in a medium lacking glucose or another preferred carbohydrate, the concentration of cAMP-cAMP receptor protein (cAMP-CRP) increases, and this latter complex regulates the expression of more than 180 genes. To respond rapidly to changes in carbohydrate availability, E. coli must maintain a suitable intracellular concentration of cAMP by either exporting or degrading excess cAMP. Currently, cAMP export via the TolC protein is thought to be more efficient at reducing these levels than is CpdA-mediated degradation of cAMP. Here, we compared the contributions of TolC and CpdA by measuring the expression of cAMP-regulated genes that encode tryptophanase (TnaA) and β-galactosidase. In the presence of exogenous cAMP, a tolC mutant produced intermediate levels of these enzymes, suggesting that cAMP levels were held in check by CpdA. Conversely, a cpdA mutant produced much higher amounts of these enzymes, indicating that CpdA was more efficient than TolC at reducing cAMP levels. Surprisingly, expression of the tnaA gene halted rapidly when glucose was added to cells lacking both TolC and CpdA, even though under these conditions cAMP could not be removed by either pathway and tnaA expression should have remained high. This result suggests the existence of an additional mechanism that eliminates intracellular cAMP or terminates expression of some cAMP-CRP-regulated genes. In addition, adding glucose and other carbohydrates rapidly inhibited the function of pre-formed TnaA, indicating that TnaA is regulated by a previously unknown carbohydrate-dependent post-translational mechanism.
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Affiliation(s)
- Gang Li
- Department of Microbiology and Immunology, University of Arkansas for Medical Sciences, Little Rock, AR 72205-7199, USA
| | - Kevin D Young
- Department of Microbiology and Immunology, University of Arkansas for Medical Sciences, Little Rock, AR 72205-7199, USA
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22
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Bordbar A, Nagarajan H, Lewis NE, Latif H, Ebrahim A, Federowicz S, Schellenberger J, Palsson BO. Minimal metabolic pathway structure is consistent with associated biomolecular interactions. Mol Syst Biol 2014; 10:737. [PMID: 24987116 PMCID: PMC4299494 DOI: 10.15252/msb.20145243] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Pathways are a universal paradigm for functionally describing cellular processes. Even though advances in high-throughput data generation have transformed biology, the core of our biological understanding, and hence data interpretation, is still predicated on human-defined pathways. Here, we introduce an unbiased, pathway structure for genome-scale metabolic networks defined based on principles of parsimony that do not mimic canonical human-defined textbook pathways. Instead, these minimal pathways better describe multiple independent pathway-associated biomolecular interaction datasets suggesting a functional organization for metabolism based on parsimonious use of cellular components. We use the inherent predictive capability of these pathways to experimentally discover novel transcriptional regulatory interactions in Escherichia coli metabolism for three transcription factors, effectively doubling the known regulatory roles for Nac and MntR. This study suggests an underlying and fundamental principle in the evolutionary selection of pathway structures; namely, that pathways may be minimal, independent, and segregated.
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Affiliation(s)
- Aarash Bordbar
- Department of Bioengineering, University of California San Diego, La Jolla, CA, USA
| | - Harish Nagarajan
- Bioinformatics and Systems Biology Program, University of California San Diego, La Jolla, CA, USA
| | - Nathan E Lewis
- Department of Bioengineering, University of California San Diego, La Jolla, CA, USA Department of Pediatrics, University of California San Diego School of Medicine, La Jolla, CA, USA Wyss Institute for Biologically Inspired Engineering and Department of Genetics, Harvard Medical School, Boston, MA, USA
| | - Haythem Latif
- Department of Bioengineering, University of California San Diego, La Jolla, CA, USA
| | - Ali Ebrahim
- Department of Bioengineering, University of California San Diego, La Jolla, CA, USA
| | - Stephen Federowicz
- Bioinformatics and Systems Biology Program, University of California San Diego, La Jolla, CA, USA
| | - Jan Schellenberger
- Bioinformatics and Systems Biology Program, University of California San Diego, La Jolla, CA, USA
| | - Bernhard O Palsson
- Department of Bioengineering, University of California San Diego, La Jolla, CA, USA Bioinformatics and Systems Biology Program, University of California San Diego, La Jolla, CA, USA Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Lyngby, Denmark
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23
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Application of a new versatile electron transfer system for cytochrome P450-based Escherichia coli whole-cell bioconversions. Appl Microbiol Biotechnol 2012; 97:7741-54. [PMID: 23254762 DOI: 10.1007/s00253-012-4612-0] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2012] [Revised: 11/14/2012] [Accepted: 11/22/2012] [Indexed: 10/27/2022]
Abstract
Cytochromes P450 monooxygenases are highly interesting biocatalysts for biotechnological applications, since they perform a diversity of reactions on a broad range of organic molecules. Nevertheless, the application of cytochromes P450 is limited compared to other enzymes mainly because of the necessity of a functional redox chain to transfer electrons from NAD(P)H to the monooxygenase. In this study, we established a novel robust redox chain based on adrenodoxin, which can deliver electrons to mitochondrial, bacterial and microsomal P450s. The natural membrane-associated reductase of adrenodoxin was replaced by the soluble Escherichia coli reductase. We could demonstrate for the first time that this reductase can transfer electrons to adrenodoxin. In the first step, the electron transfer properties and the potential of this new system were investigated in vitro, and in the second step, an efficient E. coli whole-cell system using CYP264A1 from Sorangium cellulosum So ce56 was developed. It could be demonstrated that this novel redox chain leads to an initial conversion rate of 55 μM/h, which was 52 % higher compared to the 36 μM/h of the redox chain containing adrenodoxin reductase. Moreover, we optimized the whole-cell biotransformation system by a detailed investigation of the effects of different media. Finally, we are able to demonstrate that the new system is generally applicable to other cytochromes P450 by combining it with the biotechnologically important steroid hydroxylase CYP106A2 from Bacillus megaterium.
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Cysteine catabolism and cysteine desulfhydrase (CdsH/STM0458) in Salmonella enterica serovar typhimurium. J Bacteriol 2012; 194:4366-76. [PMID: 22685283 DOI: 10.1128/jb.00729-12] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Cysteine is potentially toxic and can affect diverse functions such as oxidative stress, antibiotic resistance, and swarming motility. The contribution of cysteine catabolism in modulating responses to cysteine has not been examined, in part because the genes have not been identified and mutants lacking these genes have not been isolated or characterized. We identified the gene for a previously described cysteine desulfhydrase, which we designated cdsH (formerly STM0458). We also identified a divergently transcribed gene that regulates cdsH expression, which we designated cutR (formerly ybaO, or STM0459). CdsH appears to be the major cysteine-degrading and sulfide-producing enzyme aerobically but not anaerobically. Mutants with deletions of cdsH and ybaO exhibited increased sensitivity to cysteine toxicity and altered swarming motility but unaltered cysteine-enhanced antibiotic resistance and survival in macrophages.
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Lee JH, Park JH, Kim JA, Neupane GP, Cho MH, Lee CS, Lee J. Low concentrations of honey reduce biofilm formation, quorum sensing, and virulence in Escherichia coli O157:H7. BIOFOULING 2011; 27:1095-1104. [PMID: 22047137 DOI: 10.1080/08927014.2011.633704] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Bacterial biofilms are associated with persistent infections due to their high resistance to antimicrobial agents. Hence, controlling pathogenic biofilm formation is important in bacteria-related diseases. Honey, at a low concentration of 0.5% (v/v), significantly reduced biofilm formation in enterohemorrhagic Escherichia coli O157:H7 without inhibiting the growth of planktonic cells. Conversely, this concentration did not inhibit commensal E. coli K-12 biofilm formation. Transcriptome analyses showed that honey significantly repressed curli genes (csgBAC), quorum sensing genes (AI-2 importer and indole biosynthesis), and virulence genes (LEE genes). Glucose and fructose in the honeys were found to be key components in reducing biofilm formation by E. coli O157:H7 through the suppression of curli production and AI-2 import. Furthermore, honey, glucose and fructose decreased the colonization of E. coli O157:H7 cells on human HT-29 epithelial cells. These results suggest that low concentrations of honey, such as in honeyed water, can be a practical means for reducing the colonization and virulence of pathogenic E. coli O157:H7.
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Affiliation(s)
- Jin-Hyung Lee
- School of Chemical Engineering, Yeungnam University, Gyeongsan, 712-74, Republic of Korea
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26
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Han Y, Yang CL, Yang Q, Qi Z, Liu W, Xu ZH, Zhu WM, Bossier P, Zhang XH. Mutation of tryptophanase gene tnaA in Edwardsiella tarda reduces lipopolysaccharide production, antibiotic resistance and virulence. ENVIRONMENTAL MICROBIOLOGY REPORTS 2011; 3:603-612. [PMID: 23761341 DOI: 10.1111/j.1758-2229.2011.00269.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
A fish pathogen Edwardsiella tarda LTB-4 produced various indole alkaloids, including indole, 2-(1H-indol-3-yl)ethanol, 4-di(1H-indol-3-yl)methylphenol, tri(1H-indol-3-yl)methane and 2-[2,2-bis(1H-indol-3-yl)]ethylphenylamine. Indole was the most abundant among these indole alkaloids. E. tarda LTB-4 produced indoles during its whole growth phase and maintained a high level (around 35.5 µM) during the stationary phase. The relevant tryptophanase (TnaA) gene tnaA was cloned from LTB-4 and conditionally expressed in Escherichia coli; the recombinant TnaA catalysed L-tryptophan to indole. A tnaA in-frame deletion mutant ΔtnaA was constructed through double cross-over allelic exchange by means of the suicide vector pRE118; deletion of tnaA caused some phenotypic changes including decreased swarming and twitching motility, lipopolysaccharide production and multiple antibiotic resistances. Also, subtherapeutic doses of chloromycetin, carbenicillin and tetracyline could cause the decrease of bacterial growth, but greatly induce the production of indole by E. tarda. Most importantly, attenuated virulence of the ΔtnaA mutant to zebra fish by increasing the LD50 for about 55-fold indicated that TnaA involved in the virulence of E. tarda.
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Affiliation(s)
- Yin Han
- College of Marine Life Sciences School of Medicine and Pharmacy, Ocean University of China, Qingdao, China Laboratory of Aquaculture and Artemia Reference Center, Ghent University, Rozier 44, Gent 9000, Belgium
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MEDINA MARJORIEB, UKNALIS JOSEPH, TU SHUI. EFFECTS OF SUGAR ADDITION IN LURIA BERTANI (LB) MEDIA ON ESCHERICHIA COLI O157:H7. J Food Saf 2011. [DOI: 10.1111/j.1745-4565.2011.00311.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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CsrA and TnaB coregulate tryptophanase activity to promote exotoxin-induced killing of Caenorhabditis elegans by enteropathogenic Escherichia coli. J Bacteriol 2011; 193:4516-22. [PMID: 21705596 DOI: 10.1128/jb.05197-11] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Enteropathogenic Escherichia coli(EPEC) requires the tnaA-encoded enzyme tryptophanase and its substrate tryptophan to synthesize diffusible exotoxins that kill the nematode Caenorhabditis elegans. Here, we demonstrate that the RNA-binding protein CsrA and the tryptophan permease TnaB coregulate tryptophanase activity, through mutually exclusive pathways, to stimulate toxin-mediated paralysis and killing of C. elegans.
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29
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Kim YG, Lee JH, Cho MH, Lee J. Indole and 3-indolylacetonitrile inhibit spore maturation in Paenibacillus alvei. BMC Microbiol 2011; 11:119. [PMID: 21619597 PMCID: PMC3126691 DOI: 10.1186/1471-2180-11-119] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Accepted: 05/27/2011] [Indexed: 12/26/2022] Open
Abstract
Background Bacteria use diverse signaling molecules to ensure the survival of the species in environmental niches. A variety of both Gram-positive and Gram-negative bacteria produce large quantities of indole that functions as an intercellular signal controlling diverse aspects of bacterial physiology. Results In this study, we sought a novel role of indole in a Gram-positive bacteria Paenibacillus alvei that can produce extracellular indole at a concentration of up to 300 μM in the stationary phase in Luria-Bertani medium. Unlike previous studies, our data show that the production of indole in P. alvei is strictly controlled by catabolite repression since the addition of glucose and glycerol completely turns off the indole production. The addition of exogenous indole markedly inhibits the heat resistance of P. alvei without affecting cell growth. Observation of cell morphology with electron microscopy shows that indole inhibits the development of spore coats and cortex in P. alvei. As a result of the immature spore formation of P. alvei, indole also decreases P. alvei survival when exposed to antibiotics, low pH, and ethanol. Additionally, indole derivatives also influence the heat resistance; for example, a plant auxin, 3-indolylacetonitrile dramatically (2900-fold) decreased the heat resistance of P. alvei, while another auxin 3-indoleacetic acid had a less significant influence on the heat resistance of P. alvei. Conclusions Together, our results demonstrate that indole and plant auxin 3-indolylacetonitrile inhibit spore maturation of P. alvei and that 3-indolylacetonitrile presents an opportunity for the control of heat and antimicrobial resistant spores of Gram-positive bacteria.
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Affiliation(s)
- Yong-Guy Kim
- School of Chemical Engineering, Yeungnam University, Gyeongsan, Gyeonsangbuk-do 712-749, Korea
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30
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Han TH, Lee JH, Cho MH, Wood TK, Lee J. Environmental factors affecting indole production in Escherichia coli. Res Microbiol 2011; 162:108-16. [PMID: 21145393 PMCID: PMC3171796 DOI: 10.1016/j.resmic.2010.11.005] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2010] [Accepted: 09/17/2010] [Indexed: 01/01/2023]
Abstract
A variety of both Gram-positive and Gram-negative bacteria produce large quantities of indole as an intercellular signal in microbial communities. Biosynthesis of indole is well-studied, and while carbon sources and amino acids are important environmental cues for indole production in Escherichia coli, other environmental factors affecting indole production for this strain are less clear. This study demonstrates that the environmental cue pH is an important factor for indole production that further controls biofilm formation of E. coli. Moreover, E. coli produced a higher level of extracellular indole in the presence of the antibiotics ampicillin and kanamycin, and the increased indole enhanced cell survival during antibiotic stress. Additionally, we found here that temperature is another important factor for indole production; E. coli produces and accumulates a large amount of indole at 50 °C, even at low cell densities. Overall, our results suggest that indole is a stable biological compound, and E. coli may utilize indole to protect itself against other microorganisms.
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Affiliation(s)
- Thi Hiep Han
- School of Display & Chemical Engineering, Yeungnam University, Gyeongsan-si, Gyeonsangbuk-do 712-749, Korea
| | - Jin-Hyung Lee
- School of Display & Chemical Engineering, Yeungnam University, Gyeongsan-si, Gyeonsangbuk-do 712-749, Korea
| | - Moo Hwan Cho
- School of Display & Chemical Engineering, Yeungnam University, Gyeongsan-si, Gyeonsangbuk-do 712-749, Korea
| | - Thomas K. Wood
- Department of Chemical Engineering, 220 Jack E. Brown Building, Texas A&M University, College Station, TX 77843-3122, USA
| | - Jintae Lee
- School of Display & Chemical Engineering, Yeungnam University, Gyeongsan-si, Gyeonsangbuk-do 712-749, Korea
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Ujimaru T, Kakimoto T, Chibata I. l-Tryptophan Production by Achromobacter liquidum. Appl Environ Microbiol 2010; 46:1-5. [PMID: 16346331 PMCID: PMC239257 DOI: 10.1128/aem.46.1.1-5.1983] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Conditions for the production of tryptophanase from Achromobacter liquidum and for the conversion of l-serine and indole to l-tryptophan were studied. The enzyme could be produced in amounts as great as 0.750 U/ml (degradation) and 0.294 U/ml (synthesis) by shaking cultures at 30 degrees C in a medium containing dextrin, yeast extract, l-tryptophan, and l-glutamic acid. l-Tryptophan was produced most efficiently by shaking the cells at 37 degrees C in a reaction mixture containing 60 mg of l-serine per ml, 60 mg of indole per ml, and 0.5 mM pyridoxal phosphate. After 3 days, 96 mg of l-tryptophan per ml was formed, and l-tryptophan was easily isolated to 85.4% yield by concentration of the reaction mixture.
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Affiliation(s)
- T Ujimaru
- Research Laboratory of Applied Biochemistry, Tanabe Seiyaku Co., Ltd., Yodogawa-ku, Osaka 532, Japan
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Abstract
Bacteria can utilize signal molecules to coordinate their behavior to survive in dynamic multispecies communities. Indole is widespread in the natural environment, as a variety of both Gram-positive and Gram-negative bacteria (to date, 85 species) produce large quantities of indole. Although it has been known for over 100 years that many bacteria produce indole, the real biological roles of this molecule are only now beginning to be unveiled. As an intercellular signal molecule, indole controls diverse aspects of bacterial physiology, such as spore formation, plasmid stability, drug resistance, biofilm formation, and virulence in indole-producing bacteria. In contrast, many non-indole-producing bacteria, plants and animals produce diverse oxygenases which may interfere with indole signaling. It appears indole plays an important role in bacterial physiology, ecological balance, and possibly human health. Here we discuss our current knowledge and perspectives on indole signaling.
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Affiliation(s)
- Jin-Hyung Lee
- School of Display & Chemical Engineering, Yeungnam University, Gyeongsan, Korea
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Lee J, Maeda T, Hong SH, Wood TK. Reconfiguring the quorum-sensing regulator SdiA of Escherichia coli to control biofilm formation via indole and N-acylhomoserine lactones. Appl Environ Microbiol 2009; 75:1703-16. [PMID: 19168658 PMCID: PMC2655446 DOI: 10.1128/aem.02081-08] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2008] [Accepted: 01/10/2009] [Indexed: 11/20/2022] Open
Abstract
SdiA is a homolog of quorum-sensing regulators that detects N-acylhomoserine lactone (AHL) signals from other bacteria. Escherichia coli uses SdiA to reduce its biofilm formation in the presence of both AHLs and its own signal indole. Here we reconfigured SdiA (240 amino acids) to control biofilm formation using protein engineering. Four SdiA variants were obtained with altered biofilm formation, including truncation variants SdiA1E11 (F7L, F59L, Y70C, M94K, and K153X) and SdiA14C3 (W9R, P49T, N87T, frameshift at N96, and L123X), which reduced biofilm formation by 5- to 20-fold compared to wild-type SdiA in the presence of endogenous indole. Whole-transcriptome profiling revealed that wild-type SdiA reduced biofilm formation by repressing genes related to indole synthesis and curli synthesis compared to when no SdiA was expressed, while variant SdiA1E11 induced genes related to indole synthesis in comparison to wild-type SdiA. These results suggested altered indole metabolism, and corroborating the DNA microarray results in regard to indole synthesis, variant SdiA1E11 produced ninefold more indole, which led to reduced swimming motility and cell density. Also, wild-type SdiA decreased curli production and tnaA transcription, while SdiA1E11 increased tnaA transcription (tnaA encodes tryptophanase, which forms indole) compared to wild-type SdiA. Hence, wild-type SdiA decreased biofilm formation by reducing curli production and motility, and SdiA1E11 reduced biofilm formation via indole. Furthermore, an AHL-sensitive variant (SdiA2D10, having four mutations at E31G, Y42F, R116H, and L165Q) increased biofilm formation sevenfold in the presence of N-octanoyl-DL-homoserine lactone and N-(3-oxododecatanoyl)-L-homoserine lactone. Therefore, SdiA can be evolved to increase or decrease biofilm formation, and biofilm formation may be controlled by altering sensors rather than signals.
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Affiliation(s)
- Jintae Lee
- Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843-3122, USA
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Catabolite repression control of napF (periplasmic nitrate reductase) operon expression in Escherichia coli K-12. J Bacteriol 2008; 191:996-1005. [PMID: 19060147 DOI: 10.1128/jb.00873-08] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Escherichia coli, a facultative aerobe, expresses two distinct respiratory nitrate reductases. The periplasmic NapABC enzyme likely functions during growth in nitrate-limited environments, whereas the membrane-bound NarGHI enzyme functions during growth in nitrate-rich environments. Maximal expression of the napFDAGHBC operon encoding periplasmic nitrate reductase results from synergistic transcription activation by the Fnr and phospho-NarP proteins, acting in response to anaerobiosis and nitrate or nitrite, respectively. Here, we report that, during anaerobic growth with no added nitrate, less-preferred carbon sources stimulated napF operon expression by as much as fourfold relative to glucose. Deletion analysis identified a cyclic AMP receptor protein (Crp) binding site upstream of the NarP and Fnr sites as being required for this stimulation. The napD and nrfA operon control regions from Shewanella spp. also have apparent Crp and Fnr sites, and expression from the Shewanella oneidensis nrfA control region cloned in E. coli was subject to catabolite repression. In contrast, the carbon source had relatively little effect on expression of the narGHJI operon encoding membrane-bound nitrate reductase under any growth condition tested. Carbon source oxidation state had no influence on synthesis of either nitrate reductase. The results suggest that the Fnr and Crp proteins may act synergistically to enhance NapABC synthesis during growth with poor carbon sources to help obtain energy from low levels of nitrate.
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Isarankura-Na-Ayudhya C, Panpumthong P, Tangkosakul T, Boonpangrak S, Prachayasittikul V. Shedding light on the role of Vitreoscilla hemoglobin on cellular catabolic regulation by proteomic analysis. Int J Biol Sci 2008; 4:71-80. [PMID: 18345284 PMCID: PMC2267286 DOI: 10.7150/ijbs.4.71] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2008] [Accepted: 03/02/2008] [Indexed: 01/24/2023] Open
Abstract
Heterologous expression of Vitreoscilla hemoglobin (VHb) has been reported to improve cell growth, protein synthesis, metabolite productivity and nitric oxide detoxification. Although it has been proposed that such phenomenon is attributed to the enhancement of respiration and energy metabolism by facilitating oxygen delivery, the mechanism of VHb action remains to be elucidated. In the present study, changes of protein expression profile in Escherichia coli as a consequence of VHb production was investigated by two-dimensional gel electrophoresis (2-DE) in conjunction with peptide mass fingerprinting. Total protein extracts derived from cells expressing native green fluorescent protein (GFPuv) and chimeric VHbGFPuv grown in Luria-Bertani broth were prepared by sonic disintegration. One hundred microgram of proteins was individually electrophoresed in IEF-agarose rod gels followed by gradient SDS-PAGE gels. Protein spots were excised from the gels, digested to peptide fragments by trypsin, and analyzed using matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry. Results revealed that expression of VHbGFPuv caused an entire disappearance of tryptophanase as well as down-regulated proteins involved in various metabolic pathways, e.g. glycerol kinase, isocitrate dehydrogenase, aldehyde dehydrogenase, and D-glucose-D-galactose binding protein. Phenotypic assay of cellular indole production confirmed the differentially expressed tryptophanase enzymes in which cells expressing chimeric VHbGFP demonstrated a complete indole-negative reaction. Supplementation of δ-aminolevulinic acid (ALA) to the culture medium enhanced expression of glyceraldehyde-3-phosphate dehydrogenase and glycerol kinase. Our findings herein shed light on the functional roles of VHb on cellular carbon and nitrogen consumptions as well as regulation of other metabolic pathway intermediates, possibly by autoregulation of the catabolite repressor regulons.
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Indole is an inter-species biofilm signal mediated by SdiA. BMC Microbiol 2007; 7:42. [PMID: 17511876 PMCID: PMC1899176 DOI: 10.1186/1471-2180-7-42] [Citation(s) in RCA: 327] [Impact Index Per Article: 19.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2006] [Accepted: 05/18/2007] [Indexed: 01/07/2023] Open
Abstract
Background As a stationary phase signal, indole is secreted in large quantities into rich medium by Escherichia coli and has been shown to control several genes (e.g., astD, tnaB, gabT), multi-drug exporters, and the pathogenicity island of E. coli; however, its impact on biofilm formation has not been well-studied. Results Through a series of global transcriptome analyses, confocal microscopy, isogenic mutants, and dual-species biofilms, we show here that indole is a non-toxic signal that controls E. coli biofilms by repressing motility, inducing the sensor of the quorum sensing signal autoinducer-1 (SdiA), and influencing acid resistance (e.g., hdeABD, gadABCEX). Isogenic mutants showed these associated proteins are directly related to biofilm formation (e.g., the sdiA mutation increased biofilm formation 50-fold), and SdiA-mediated transcription was shown to be influenced by indole. The reduction in motility due to indole addition results in the biofilm architecture changing from scattered towers to flat colonies. Additionally, there are 12-fold more E. coli cells in dual-species biofilms grown in the presence of Pseudomonas cells engineered to express toluene o-monooxygenase (TOM, which converts indole to an insoluble indigoid) than in biofilms with pseudomonads that do not express TOM due to a 22-fold reduction in extracellular indole. Also, indole stimulates biofilm formation in pseudomonads. Further evidence that the indole effects are mediated by SdiA and homoserine lactone quorum sensing is that the addition of N-butyryl-, N-hexanoyl-, and N-octanoyl-L-homoserine lactones repress E. coli biofilm formation in the wild-type strain but not with the sdiA mutant. Conclusion Indole is an interspecies signal that decreases E. coli biofilms through SdiA and increases those of pseudomonads. Indole may be manipulated to control biofilm formation by oxygenases of bacteria that do not synthesize it in a dual-species biofilm. Furthermore, E. coli changes its biofilm in response to signals it cannot synthesize (homoserine lactones), and pseudomonads respond to signals they do not synthesize (indole).
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Bordi C, Théraulaz L, Méjean V, Jourlin-Castelli C. Anticipating an alkaline stress through the Tor phosphorelay system in Escherichia coli. Mol Microbiol 2003; 48:211-23. [PMID: 12657056 DOI: 10.1046/j.1365-2958.2003.03428.x] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The torCAD operon encoding the TMAO reductase respiratory system is induced in the presence of TMAO by the two-component regulatory system TorS/TorR. The TorS sensor detects TMAO and transphosphorylates the TorR response regulator via a four-step phosphorelay. Once phosphorylated, TorR activates expression of the torCAD structural operon. In order to identify new genes regulated by the Tor regulatory system, we performed a genome-wide transcriptional analysis by using the DNA array technology. We identified seven new transcriptional units whose expression is modulated by the TorS/TorR phosphorelay system. One unit, tnaLAB, is positively regulated whereas the other six, gadA, gadBC, hdeAB, hdeD, yhiE and yhiM, are negatively regulated by this system. Interestingly, the products of some of these units seem to play a role in the survival of E. coli in conditions of extreme pH. The TnaA tryptophanase has been proposed to counteract alkaline stress, whereas the GadA and GadB glutamate decarboxylases and the HdeA and HdeB proteins are involved in the defence against acid stress. Our hypothesis is that the TorS/TorR phosphorelay triggers alkaline-stress defence to limit alkalinization resulting from the reduction of TMAO in alkaline TMA by the Tor respiratory system. The fact that a DeltatnaLAB mutant showed a dramatic decrease in survival as a result of TMAO respiration is in agreement with such a model. As regulation of these genes by the TorS/TorR system does not depend on pH modification but rather on the presence of TMAO, we propose that E. coli anticipates alkalinization of the medium due to TMA production by base-resistance gene activation and acid-resistance gene repression.
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Affiliation(s)
- Christophe Bordi
- Laboratoire de Chimie Bactérienne, Institut de Biologie Structurale et Microbiologie, Centre National de la Recherche Scientifique, 31 chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
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39
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Abstract
Expression of the tryptophanase operon of Escherichia coli is regulated by catabolite repression and tryptophan-induced transcription antitermination. An induction site activated by l-tryptophan is created in the translating ribosome during synthesis of TnaC, the 24-residue leader peptide. Replacing the tnaC stop codon with a tryptophan codon allows tryptophan-charged tryptophan transfer RNA to substitute for tryptophan as inducer. This suggests that the ribosomal A site occupied by the tryptophanyl moiety of the charged transfer RNA is the site of induction. The location of tryptophan-12 of nascent TnaC in the peptide exit tunnel was crucial for induction. These results show that a nascent peptide sequence can influence translation continuation and termination within a translating ribosome.
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Affiliation(s)
- Feng Gong
- Department of Biological Sciences, Stanford University, Stanford, CA 94305, USA
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40
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Gong F, Yanofsky C. Analysis of tryptophanase operon expression in vitro: accumulation of TnaC-peptidyl-tRNA in a release factor 2-depleted S-30 extract prevents Rho factor action, simulating induction. J Biol Chem 2002; 277:17095-100. [PMID: 11880383 DOI: 10.1074/jbc.m201213200] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Expression of the tryptophanase (tna) operon in Escherichia coli is regulated by catabolite repression and tryptophan-induced transcription antitermination. The key feature of this antitermination mechanism has been shown to be the retention of uncleaved TnaC-peptidyl-tRNA in the translating ribosome. This ribosome remains stalled at the tna stop codon and blocks the access of Rho factor to the tna transcript, thereby preventing transcription termination. In normal S-30 preparations, synthesis of a TnaC peptide containing arginine instead of tryptophan at position 12 (Arg(12)-TnaC) was shown to be insensitive to added tryptophan, i.e. Arg(12)-TnaC-peptidyl-tRNA was cleaved, and there was normal Rho-dependent transcription termination. When the S-30 extract used was depleted of release factor 2, Arg(12)-TnaC-tRNA(Pro) was accumulated in the absence or presence of added tryptophan. Under these conditions the accumulation of Arg(12)-TnaC-tRNA(Pro) prevented Rho-dependent transcription termination, mimicking normal induction. Using a minimal in vitro transcription system consisting of a tna template, RNA polymerase, and Rho, it was shown that RNA sequences immediately adjacent to the tnaC stop codon, the presumed boxA and rut sites, contributed most significantly to Rho-dependent termination. The tna boxA-like sequence appeared to serve as a segment of the Rho "entry" site, despite its likeness to the boxA element.
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Affiliation(s)
- Feng Gong
- Department of Biological Sciences, Stanford University, Stanford, California 94305-5020, USA
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41
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Gong F, Ito K, Nakamura Y, Yanofsky C. The mechanism of tryptophan induction of tryptophanase operon expression: tryptophan inhibits release factor-mediated cleavage of TnaC-peptidyl-tRNA(Pro). Proc Natl Acad Sci U S A 2001; 98:8997-9001. [PMID: 11470925 PMCID: PMC55362 DOI: 10.1073/pnas.171299298] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Expression of the tryptophanase (tna) operon of Escherichia coli is regulated by catabolite repression and tryptophan-induced transcription antitermination. In a previous study, we reproduced the regulatory features of this operon observed in vivo by using an in vitro S-30 system. We also found that, under inducing conditions, the leader peptidyl-tRNA (TnaC-peptidyl-tRNA(Pro)) is not cleaved; it accumulates in the S-30 reaction mixture. In this paper, we examine the requirements for TnaC-peptidyl-tRNA(Pro) accumulation and cleavage, in vitro. We show that this peptidyl-tRNA remains bound to the translating ribosome. Removal of free tryptophan and addition of release factor 1 or 2 leads to hydrolysis of TnaC-peptidyl-tRNA(Pro) and release of TnaC from the ribosome-mRNA complex. Release factor-mediated cleavage is prevented by the addition of tryptophan. TnaC of the ribosome-bound TnaC-peptidyl-tRNA(Pro) was transferable to puromycin. This transfer was also blocked by tryptophan. Tests with various tryptophan analogs as substitutes for tryptophan revealed the existence of strict structural requirements for tryptophan action. Our findings demonstrate that the addition of tryptophan to ribosomes bearing nascent TnaC-peptidyl-tRNA(Pro) inhibits both TnaC peptidyl-tRNA(Pro) hydrolysis and TnaC peptidyl transfer. The associated translating ribosome therefore remains attached to the leader transcript where it blocks Rho factor binding and subsequent transcription termination.
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Affiliation(s)
- F Gong
- Department of Biological Sciences, Stanford University, Stanford, CA 94305; and Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedal, Minato-Ku, Tokyo 108-8639, Japan
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Gong F, Yanofsky C. Reproducing tna operon regulation in vitro in an S-30 system. Tryptophan induction inhibits cleavage of TnaC peptidyl-tRNA. J Biol Chem 2001; 276:1974-83. [PMID: 11050101 DOI: 10.1074/jbc.m008892200] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Expression of the tryptophanase (tna) operon of Escherichia coli is regulated by catabolite repression and tryptophan-induced transcription antitermination. Catabolite repression regulates transcription initiation, whereas excess tryptophan induces antitermination at Rho factor-dependent termination sites in the leader region of the operon. Synthesis of the leader peptide, TnaC, is essential for antitermination. BoxA and rut sites in the immediate vicinity of the tnaC stop codon are required for termination. In this paper we use an in vitro S-30 cell-free system to analyze the features of tna operon regulation. We show that transcription initiation is cyclic AMP (cAMP)-dependent and is not influenced by tryptophan. Continuation of transcription beyond the leader region requires the presence of inducing levels of tryptophan and synthesis of the TnaC leader peptide. Using a tnaA'-'trpE fusion, we demonstrate that induction results in a 15-20-fold increase in synthesis of the tryptophan-free TnaA-TrpE fusion protein. Replacing Trp codon 12 of tnaC by an Arg codon, or changing the tnaC start codon to a stop codon, eliminates induction. Addition of bicyclomycin, a specific inhibitor of Rho factor action, substantially increases basal level expression. Analyses of tna mRNA synthesis in vitro demonstrate that, in the absence of inducer transcription is terminated and the terminated transcripts are degraded. In the presence of inducer, antitermination increases the synthesis of the read-through transcript. TnaC synthesis is observed in the cell-free system. However, in the presence of tryptophan, a peptidyl-tRNA also appears, TnaC-tRNA(Pro). Our findings suggest that inducer acts by preventing cleavage of TnaC peptidyl-tRNA. The ribosome associated with this newly synthesized peptidyl-tRNA presumably stalls at the tnaC stop codon, blocking Rho's access to the BoxA and rut sites, thereby preventing termination. 1-Methyltryptophan also is an effective inducer in vitro. This tryptophan analog is not incorporated into TnaC.
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Affiliation(s)
- F Gong
- Department of Biological Sciences, Stanford University, Stanford, California 94305, USA
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Konan KV, Yanofsky C. Rho-dependent transcription termination in the tna operon of Escherichia coli: roles of the boxA sequence and the rut site. J Bacteriol 2000; 182:3981-8. [PMID: 10869076 PMCID: PMC94583 DOI: 10.1128/jb.182.14.3981-3988.2000] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Expression of the tryptophanase (tna) operon of Escherichia coli is regulated by catabolite repression and by tryptophan-induced transcription antitermination. Tryptophan induction prevents Rho-dependent transcription termination in the leader region of the operon. Induction requires translation of a 24-residue leader peptide-coding region, tnaC, containing a single, crucial Trp codon. Studies with a lacZ reporter construct lacking the tnaC-tnaA spacer region suggest that, in the presence of excess tryptophan, the TnaC leader peptide acts in cis on the ribosome translating tnaC to inhibit its release. The stalled ribosome is thought to block Rho's access to the transcript. In this paper we examine the roles of the boxA sequence and the rut site in Rho-dependent termination. Deleting six nucleotides (CGC CCT) of boxA or introducing specific point mutations in boxA results in high-level constitutive expression. Some constitutive changes introduced in boxA do not change the TnaC peptide sequence. We confirm that deletion of the rut site results in constitutive expression. We also demonstrate that, in each constitutive construct, replacement of the tnaC start codon by a UAG stop codon reduces expression significantly, suggesting that constitutive expression requires translation of the tnaC coding sequence. Addition of bicyclomycin, an inhibitor of Rho, to these UAG constructs increases expression, demonstrating that reduced expression is due to Rho action. Combining a boxA point mutation with rut site deletion results in constitutive expression comparable to that of a maximally induced operon. These results support the hypothesis that in the presence of tryptophan the ribosome translating tnaC blocks Rho's access to the boxA and rut sites, thereby preventing transcription termination.
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Affiliation(s)
- K V Konan
- Department of Biological Sciences, Stanford University, CA 94305-5020, USA
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Konan KV, Yanofsky C. Role of ribosome release in regulation of tna operon expression in Escherichia coli. J Bacteriol 1999; 181:1530-6. [PMID: 10049385 PMCID: PMC93543 DOI: 10.1128/jb.181.5.1530-1536.1999] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Expression of the degradative tryptophanase (tna) operon of Escherichia coli is regulated by catabolite repression and tryptophan-induced transcription antitermination. In cultures growing in the absence of added tryptophan, transcription of the structural genes of the tna operon is limited by Rho-dependent transcription termination in the leader region of the operon. Tryptophan induction prevents this Rho-dependent termination, and requires in-frame translation of a 24-residue leader peptide coding region, tnaC, that contains a single, crucial, Trp codon. Studies with a lacZ reporter construct lacking the spacer region between tnaC and the first major structural gene, tnaA, suggested that tryptophan induction might involve cis action by the TnaC leader peptide on the ribosome translating the tnaC coding region. The leader peptide was hypothesized to inhibit ribosome release at the tnaC stop codon, thereby blocking Rho's access to the transcript. Regulatory studies with deletion constructs of the tna operon of Proteus vulgaris supported this interpretation. In the present study the putative role of the tnaC stop codon in tna operon regulation in E. coli was examined further by replacing the natural tnaC stop codon, UGA, with UAG or UAA in a tnaC-stop codon-tnaA'-'lacZ reporter construct. Basal level expression was reduced to 20 and 50% when the UGA stop codon was replaced by UAG or UAA, respectively, consistent with the finding that in E. coli translation terminates more efficiently at UAG and UAA than at UGA. Tryptophan induction was observed in strains with any of the stop codons. However, when UAG or UAA replaced UGA, the induced level of expression was also reduced to 15 and 50% of that obtained with UGA as the tnaC stop codon, respectively. Introduction of a mutant allele encoding a temperature-sensitive release factor 1, prfA1, increased basal level expression 60-fold when the tnaC stop codon was UAG and 3-fold when this stop codon was UAA; basal level expression was reduced by 50% in the construct with the natural stop codon, UGA. In strains with any of the three stop codons and the prfA1 mutation, the induced levels of tna operon expression were virtually identical. The effects of tnaC stop codon identity on expression were also examined in the absence of Rho action, using tnaC-stop codon-'lacZ constructs that lack the tnaC-tnaA spacer region. Expression was low in the absence of tnaC stop codon suppression. In most cases, tryptophan addition resulted in about 50% inhibition of expression when UGA was replaced by UAG or UAA and the appropriate suppressor was present. Introduction of the prfA1 mutant allele increased expression of the suppressed construct with the UAG stop codon; tryptophan addition also resulted in ca. 50% inhibition. These findings provide additional evidence implicating the behavior of the ribosome translating tnaC in the regulation of tna operon expression.
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Affiliation(s)
- K V Konan
- Department of Biological Sciences, Stanford University, Stanford, California 94305-5020, USA
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Rondard P, Bedouelle H. A mutational approach shows similar mechanisms of recognition for the isolated and integrated versions of a protein epitope. J Biol Chem 1998; 273:34753-9. [PMID: 9856999 DOI: 10.1074/jbc.273.52.34753] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Antibody mAb164 is directed against the native form of the TrpB2 subunit of Escherichia coli tryptophan synthase. It recognizes a synthetic peptide, P11, constituted of residues 273-283 of TrpB, with high affinity. We introduced 16 single and 3 double mutations in each of the two contexts, TrpB2 and P11, and used them as local probes to study the cross-reactivity of mAb164 toward these two antigens. The equilibrium constant, KD, of dissociation from mAb164 was measured for each of the mutant derivatives of TrpB2 and P11 by a competition enzyme-linked immunosorbent assay and compared with the wild type one. The variation of the free energy of interaction, DeltaDeltaG, covered nearly 8 kcal/mol for the different mutations. The values of DeltaDeltaG for the mutant derivatives of TrpB2 and for those of P11 were close and the two sets of values were strongly correlated (r = 0.96). This correlation showed that mAb164 recognized the integrated and isolated versions of residues 273-283 with very similar mechanisms. A few significant differences between the recognitions of TrpB2 and P11 by mAb164 suggested some adaptability of the interaction. The results were compatible with a recognition of residues 273-283 of TrpB in a loop conformation, close to their structure in the crystals of the complete tryptophan synthase, TrpA2TrpB2.
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Affiliation(s)
- P Rondard
- Groupe d'Ingénierie des Protéines (CNRS URA 1129), Unité de Biochimie Cellulaire, Institut Pasteur, 28 rue du Docteur Roux, 75724 Paris Cedex 15, France
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Abstract
The ability of microorganisms to degrade L-tyrosine to phenol, pyruvate, and ammonia is catalyzed by the inducible enzyme L-tyrosine phenol lyase (EC 4.1.99.2). To investigate possible mechanisms for how the synthesis of this enzyme is regulated, a variety of biochemical and genetic procedures was used to analyze transcription from the tpl promoter of Citrobacter freundii ATCC 29063 (C. braakii). By computer analysis of the region upstream of the tpl structural gene, two segments of DNA bearing strong homology to the known operator targets of the TyrR protein of Escherichia coli were detected. A DNA fragment of 509 bp carrying these operator targets plus the presumptive tpl promoter was synthesized by PCR and used to construct a single-copy tpl-lacZ reporter system. The formation of beta-galactosidase in strains carrying this reporter system, which was measured in E. coli strains of various genotypes, was strongly dependent on the presence of a functional TyrR protein. In strains bearing deletions of the tyrR gene, the formation of beta-galactosidase was reduced by a factor of 10. Several mutationally altered forms of TyrR were deficient in their abilities to activate the tpl promoter. The pattern of loss of activation function was exactly parallel to the effects of the same tyrR mutations on the mtr promoter, which is known to be activated by the TyrR protein. When cells carrying the tpl-lacZ reporter system were grown on glycerol, the levels of beta-galactosidase were 10- to 20-fold higher than those observed in glucose-grown cells. The effect was the same whether or not TyrR-mediated stimulation of the tpl promoter was in effect. By deleting the cya gene, it was shown that the glycerol effect was attributable to stimulation of the tpl promoter by the cyclic AMP (cAMP)-cAMP reporter protein system. A presumptive binding site for this transcription factor was detected just upstream of the -35 recognition hexamer of the tpl promoter. The transcriptional start point of the tpl promoter was determined by chemical procedures. The precise locations of the TyrR binding sites, which were established by DNase I footprinting, agreed with the computer-predicted positions of these regulatory sites. The two TyrR operators, which were centered at coordinates -272.5 and -158.5 with respect to the transcriptional start point, were independently disabled by site-directed mutagenesis. When the upstream operator was altered, activation was completely abolished. When the downstream operator was altered, there was a fourfold reduction in reporter enzyme levels. The tpl system presents a number of intriguing features not previously encountered in TyrR-activated promoters. First among these is the question of how the TyrR protein, bound to widely separated operators, activates the tpl promoter which is also widely separated from the operators.
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Affiliation(s)
- H Q Smith
- Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907, USA
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Konan KV, Yanofsky C. Regulation of the Escherichia coli tna operon: nascent leader peptide control at the tnaC stop codon. J Bacteriol 1997; 179:1774-9. [PMID: 9045840 PMCID: PMC178893 DOI: 10.1128/jb.179.5.1774-1779.1997] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Expression of the tryptophanase (tna) operon of Escherichia coli is regulated by catabolite repression and by tryptophan-induced transcription antitermination at Rho-dependent termination sites in the leader region of the operon. Tryptophan induction is dependent on translation of a short leader peptide coding region, tnaC, that contains a single, crucial tryptophan codon. Recent studies suggest that during induction, the TnaC leader peptide acts in cis on the translating ribosome to inhibit its release at the tnaC stop codon. In the present study we use a tnaC-UGA-'lacZ construct lacking the tnaC-tnaA spacer region to analyze the effect of TnaC synthesis on the behavior of the ribosome that translates tnaC. The tnaC-UGA-'lacZ construct is not expressed significantly in the presence or absence of inducer. However, it is expressed in the presence of UGA suppressors, or when the structural gene for polypeptide release factor 3 is disrupted, or when wild-type tRNATrP is overproduced. In each situation, tnaC-UGA-'lacZ expression is reduced appreciably by the presence of inducing levels of tryptophan. Replacing the tnaC UGA stop codon with a sense codon allows considerable expression, which is also reduced, although to a lesser extent, by the addition of tryptophan. Inhibition by tryptophan is not observed when Trp codon 12 of tnaC is changed to a Leu codon. Overexpression of tnaC in trans from a multicopy plasmid prevents inhibition of expression by tryptophan. These results support the hypothesis that the TnaC leader peptide acts in cis to alter the behavior of the translating ribosome.
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Affiliation(s)
- K V Konan
- Department of Biological Sciences, Stanford University, California 94305-5020, USA
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Kamath AV, Yanofsky C. Roles of the tnaC-tnaA spacer region and Rho factor in regulating expression of the tryptophanase operon of Proteus vulgaris. J Bacteriol 1997; 179:1780-6. [PMID: 9045841 PMCID: PMC178894 DOI: 10.1128/jb.179.5.1780-1786.1997] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
To localize the DNA regions responsible for basal-level and induced expression of the tryptophanase (tna) operon of Proteus vulgaris, short deletions were introduced in the 115-bp spacer region separating tnaC, the leader peptide coding region, from tnaA. Deletions were incorporated into a tnaA'-'lacZ reporter construct containing the intact tna promoter-leader region. Expression was examined in Escherichia coli. Deletions that removed 28 to 30 bp from the region immediately following tnaC increased basal-level expression about threefold and allowed threefold induction by 1-methyltryptophan. A deletion removing 34 bp from the distal segment of the leader permitted basal and induced expression comparable to that of the parental construct. The mutant with the largest spacer deletion, 89 bp, exhibited a 30-fold increase in basal-level expression, and most importantly, inducer presence reduced operon expression by ca. 60%. Replacing the tnaC start codon or replacing or removing Trp codon 20 of tnaC of this deletion derivative eliminated inducer inhibition of expression. These findings suggest that the spacer region separating tnaC and tnaA is essential for Rho action. They also suggest that juxtaposition of the tnaC stop codon and the tnaA ribosome binding site in the 89-bp deletion derivative allows the ribosome that has completed translation of tnaC to inhibit translation initiation at the tnaA start codon when cells are exposed to inducer. These findings are consistent with results in the companion article that suggest that inducer allows the TnaC peptide to inhibit ribosome release at the tnaC stop codon.
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Affiliation(s)
- A V Kamath
- Department of Molecular Sciences, Central Research Division, Pfizer Inc., Groton, Connecticut 06340, USA
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Yanofsky C, Horn V, Nakamura Y. Loss of overproduction of polypeptide release factor 3 influences expression of the tryptophanase operon of Escherichia coli. J Bacteriol 1996; 178:3755-62. [PMID: 8682777 PMCID: PMC232633 DOI: 10.1128/jb.178.13.3755-3762.1996] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Expression of the tryptophanase (tna) operon of Escherichia coli is regulated by catabolite repression and by tryptophan-induced inhibition of Rho-mediated transcription termination. Previous studies indicated that tryptophan induction might involve leader peptide inhibition of ribosome release at the stop codon of tnaC, the coding region for the operon-specified leader peptide. In this study we examined tna operon expression in strains in which the structural gene for protein release factor 3, prfC, is either disrupted or overexpressed. We find that prfC inactivation leads to a two- to threefold increase in basal expression of the tna operon and a slight increase in induced expression. Overexpression of prfC has the opposite effect and reduces both basal and induced expression. These effects occur in the presence of glucose and cyclic AMP, and thus Rho-dependent termination rather than catabolite repression appears to be the event influenced by the prfC alterations. prfC inactivation also leads to an increase in basal tna operon expression in various rho and rpoB mutants but not in a particular rho mutant in which the basal level of expression is very high. The effect of prfC inactivation was examined in a variety of mutants with alterations in the tna leader region. Our results suggest that translation of tnaC is essential for the prfC effect. The tryptophan residue specified by tnaC codon 12, which is essential for induction, when replaced by another amino) acid, allows the prfC effect. Introducing UAG or UAA stop codons rather than the normal tnaC UGA stop codon, in a strain with an inactive prfC gene, also leads to an increase in the basal level of expression. Addition of the drug bicyclomycin increases basal operon expression of all mutant strains except a strain with a tnaC'-'lacZ fusion. Expression in the latter strain is unaffected by prfC alterations. Our findings are consistent with the interpretation that ribosome release at the tnaC stop codon can influence tna operon expression.
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Affiliation(s)
- C Yanofsky
- Department of Biological Sciences, Stanford University, California 94305, USA
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50
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Abstract
A variety of transcription attenuation mechanisms are used by bacteria to regulate gene and operon expression. This review summarizes previous and current studies designed to elucidate the features of the specific attenuation mechanisms that regulate expression of the tryptophanase (tna) operon of Escherichia coli and the tryptophan (trp) operon of Bacillus subtilis. Initiation of transcription in the tna operon is regulated by catabolite repression. Once initiated, transcription is regulated by tryptophan-induced inhibition of Rho-mediated transcription termination in the leader region of the operon. An operon-encoded leader peptide, TnaC, containing a crucial tryptophan residue, plays an essential role in induction. This peptide appears to act in cis on the ribosome translating tnaC to inhibit its release at the tnaC stop codon. The stalled ribosome would block Rho's access to the tna transcript, thereby preventing termination. Transcription of the trp operon of B subtilis is regulated by an attenuation mechanism that responds to a tryptophan-activated eleven subunit RNA-binding regulatory protein, called TRAP. Activated TRAP binds to repeated GAG sequences in the leader segment of the trp operon transcript, disrupting an RNA antiterminator and promoting formation of a terminator. Activated TRAP also regulates translation of trpG in the folate operon by binding to repeat GAG sequences surrounding the trpG ribosome binding site. A temperature sensitive tryptophanyl-tRNA synthetase (trpS) mutant was previously observed to overexpress the trp operon and trpG, when grown at elevated temperatures in the presence of tryptophan. We have found that the trpS defect increases trp operon and trpG expression by interfering with TRAP's ability to act. We suggest that either accumulation of uncharged tRNA(Trp) or overproduction of a TRAP-binding transcript reduces the level of functional TRAP in the trpS mutant.
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Affiliation(s)
- C Yanofsky
- Department of Biological Sciences, Stanford University, CA 94305, USA
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