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Mandel C, Yang H, Buchko GW, Abendroth J, Grieshaber N, Chiarelli T, Grieshaber S, Omsland A. Expression and structure of the Chlamydia trachomatis DksA ortholog. Pathog Dis 2022; 80:6564600. [PMID: 35388904 PMCID: PMC9126822 DOI: 10.1093/femspd/ftac007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Revised: 02/15/2022] [Accepted: 04/04/2022] [Indexed: 11/14/2022] Open
Abstract
Chlamydia trachomatis is a bacterial obligate intracellular parasite and a significant cause of human disease, including sexually transmitted infections and trachoma. The bacterial RNA polymerase-binding protein DksA is a transcription factor integral to the multicomponent bacterial stress response pathway known as the stringent response. The genome of C. trachomatis encodes a DksA ortholog (DksACt) that is maximally expressed at 15–20 h post infection, a time frame correlating with the onset of transition between the replicative reticulate body (RB) and infectious elementary body (EB) forms of the pathogen. Ectopic overexpression of DksACt in C. trachomatis prior to RB–EB transitions during infection of HeLa cells resulted in a 39.3% reduction in overall replication (yield) and a 49.6% reduction in recovered EBs. While the overall domain organization of DksACt is similar to the DksA ortholog of Escherichia coli (DksAEc), DksACt did not functionally complement DksAEc. Transcription of dksACt is regulated by tandem promoters, one of which also controls expression of nrdR, encoding a negative regulator of deoxyribonucleotide biosynthesis. The phenotype resulting from ectopic expression of DksACt and the correlation between dksACt and nrdR expression is consistent with a role for DksACt in the C. trachomatis developmental cycle.
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Affiliation(s)
- Cameron Mandel
- Paul G. Allen School for Global Health, Washington State University, Pullman, WA 99164, USA
| | - Hong Yang
- Paul G. Allen School for Global Health, Washington State University, Pullman, WA 99164, USA
| | - Garry W Buchko
- School of Molecular Biosciences, Washington State University, Pullman WA 99164, USA.,Earth and Biological Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99354, USA.,Seattle Structural Genomics Center for Infectious Disease, WA, USA
| | - Jan Abendroth
- Seattle Structural Genomics Center for Infectious Disease, WA, USA.,UCB, Bainbridge Island, WA 98110, USA
| | - Nicole Grieshaber
- Department of Biological Sciences, University of Idaho, Moscow, ID 83844, USA
| | - Travis Chiarelli
- Department of Biological Sciences, University of Idaho, Moscow, ID 83844, USA
| | - Scott Grieshaber
- Department of Biological Sciences, University of Idaho, Moscow, ID 83844, USA
| | - Anders Omsland
- Paul G. Allen School for Global Health, Washington State University, Pullman, WA 99164, USA
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Abstract
Accumulation of phosphorylated intermediates during cellular metabolism can have wide-ranging toxic effects on many organisms, including humans and the pathogens that infect them. These toxicities can be induced by feeding an upstream metabolite (a sugar, for instance) while simultaneously blocking the appropriate metabolic pathway with either a mutation or an enzyme inhibitor. Here, we survey the toxicities that can arise in the metabolism of glucose, galactose, fructose, fructose-asparagine, glycerol, trehalose, maltose, mannose, mannitol, arabinose, and rhamnose. Select enzymes in these metabolic pathways may serve as novel therapeutic targets. Some are conserved broadly among prokaryotes and eukaryotes (e.g., glucose and galactose) and are therefore unlikely to be viable drug targets. However, others are found only in bacteria (e.g., fructose-asparagine, rhamnose, and arabinose), and one is found in fungi but not in humans (trehalose). We discuss what is known about the mechanisms of toxicity and how resistance is achieved in order to identify the prospects and challenges associated with targeted exploitation of these pervasive metabolic vulnerabilities.
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Opening a Novel Biosynthetic Pathway to Dihydroxyacetone and Glycerol in Escherichia coli Mutants through Expression of a Gene Variant ( fsaAA129S) for Fructose 6-Phosphate Aldolase. Int J Mol Sci 2020; 21:ijms21249625. [PMID: 33348713 PMCID: PMC7767278 DOI: 10.3390/ijms21249625] [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: 11/15/2020] [Revised: 12/05/2020] [Accepted: 12/15/2020] [Indexed: 01/19/2023] Open
Abstract
Phosphofructokinase (PFK) plays a pivotal role in glycolysis. By deletion of the genes pfkA, pfkB (encoding the two PFK isoenzymes), and zwf (glucose 6-phosphate dehydrogenase) in Escherichia coli K-12, a mutant strain (GL3) with a complete block in glucose catabolism was created. Introduction of plasmid-borne copies of the fsaA wild type gene (encoding E. coli fructose 6-phosphate aldolase, FSAA) did not allow a bypass by splitting fructose 6-phosphate (F6P) into dihydroxyacetone (DHA) and glyceraldehyde 3-phosphate (G3P). Although FSAA enzyme activity was detected, growth on glucose was not reestablished. A mutant allele encoding for FSAA with an amino acid exchange (Ala129Ser) which showed increased catalytic efficiency for F6P, allowed growth on glucose with a µ of about 0.12 h−1. A GL3 derivative with a chromosomally integrated copy of fsaAA129S (GL4) grew with 0.05 h−1 on glucose. A mutant strain from GL4 where dhaKLM genes were deleted (GL5) excreted DHA. By deletion of the gene glpK (glycerol kinase) and overexpression of gldA (of glycerol dehydrogenase), a strain (GL7) was created which showed glycerol formation (21.8 mM; yield approximately 70% of the theoretically maximal value) as main end product when grown on glucose. A new-to-nature pathway from glucose to glycerol was created.
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Sugar-Phosphate Metabolism Regulates Stationary-Phase Entry and Stalk Elongation in Caulobacter crescentus. J Bacteriol 2020; 202:JB.00468-19. [PMID: 31767777 DOI: 10.1128/jb.00468-19] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2019] [Accepted: 11/17/2019] [Indexed: 12/28/2022] Open
Abstract
Bacteria have a variety of mechanisms for adapting to environmental perturbations. Changes in oxygen availability result in a switch between aerobic and anaerobic respiration, whereas iron limitation may lead to siderophore secretion. In addition to metabolic adaptations, many organisms respond by altering their cell shape. Caulobacter crescentus, when grown under phosphate-limiting conditions, dramatically elongates its polar stalk appendage. The stalk is hypothesized to facilitate phosphate uptake; however, the mechanistic details of stalk synthesis are not well characterized. We used a chemical mutagenesis approach to isolate and characterize stalk-deficient mutants, one of which had two mutations in the phosphomannose isomerase gene (manA) that were necessary and sufficient to inhibit stalk elongation. Transcription of the pho regulon was unaffected in the manA mutant; therefore, ManA plays a unique regulatory role in stalk synthesis. The mutant ManA had reduced enzymatic activity, resulting in a 5-fold increase in the intracellular fructose 6-phosphate/mannose 6-phosphate ratio. This metabolic imbalance impaired the synthesis of cellular envelope components derived from mannose 6-phosphate, namely, lipopolysaccharide O-antigen and exopolysaccharide. Furthermore, the manA mutations prevented C. crescentus cells from efficiently entering stationary phase. Deletion of the stationary-phase response regulator gene spdR inhibited stalk elongation in wild-type cells, while overproduction of the alarmone ppGpp, which triggers growth arrest and stationary-phase entry, increased stalk length in the manA mutant strain. These results demonstrate that sugar-phosphate metabolism regulates stalk elongation independently of phosphate starvation.IMPORTANCE Metabolic control of bacterial cell shape is an important mechanism for adapting to environmental perturbations. Caulobacter crescentus dramatically elongates its polar stalk appendage in response to phosphate starvation. To investigate the mechanism of this morphological adaptation, we isolated stalk-deficient mutants, one of which had mutations in the phosphomannose isomerase gene (manA) that blocked stalk elongation, despite normal activation of the phosphate starvation response. The mutant ManA resulted in an imbalance in sugar-phosphate concentrations, which had effects on the synthesis of cellular envelope components and entry into stationary phase. Due to the interconnectivity of metabolic pathways, our findings may suggest more generally that the modulation of bacterial cell shape involves the regulation of growth phase and the synthesis of cellular building blocks.
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Impact of CO 2/HCO 3 - Availability on Anaplerotic Flux in Pyruvate Dehydrogenase Complex-Deficient Corynebacterium glutamicum Strains. J Bacteriol 2019; 201:JB.00387-19. [PMID: 31358612 DOI: 10.1128/jb.00387-19] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Accepted: 07/19/2019] [Indexed: 11/20/2022] Open
Abstract
The pyruvate dehydrogenase complex (PDHC) catalyzes the oxidative decarboxylation of pyruvate, yielding acetyl coenzyme A (acetyl-CoA) and CO2 The PDHC-deficient Corynebacterium glutamicum ΔaceE strain therefore lacks an important decarboxylation step in its central metabolism. Additional inactivation of pyc, encoding pyruvate carboxylase, resulted in a >15-h lag phase in the presence of glucose, while no growth defect was observed on gluconeogenetic substrates, such as acetate. Growth was successfully restored by deletion of ptsG, encoding the glucose-specific permease of the phosphotransferase system (PTS), thereby linking the observed phenotype to the increased sensitivity of the ΔaceE Δpyc strain to glucose catabolism. In this work, the ΔaceE Δpyc strain was used to systematically study the impact of perturbations of the intracellular CO2/HCO3 - pool on growth and anaplerotic flux. Remarkably, all measures leading to enhanced CO2/HCO3 - levels, such as external addition of HCO3 -, increasing the pH, or rerouting metabolic flux via the pentose phosphate pathway, at least partially eliminated the lag phase of the ΔaceE Δpyc strain on glucose medium. In accordance with these results, inactivation of the urease enzyme, lowering the intracellular CO2/HCO3 - pool, led to an even longer lag phase, accompanied by the excretion of l-valine and l-alanine. Transcriptome analysis, as well as an adaptive laboratory evolution experiment with the ΔaceE Δpyc strain, revealed the reduction of glucose uptake as a key adaptive measure to enhance growth on glucose-acetate mixtures. Taken together, our results highlight the significant impact of the intracellular CO2/HCO3 - pool on metabolic flux distribution, which becomes especially evident in engineered strains exhibiting low endogenous CO2 production rates, as exemplified by PDHC-deficient strains.IMPORTANCE CO2 is a ubiquitous product of cellular metabolism and an essential substrate for carboxylation reactions. The pyruvate dehydrogenase complex (PDHC) catalyzes a central metabolic reaction contributing to the intracellular CO2/HCO3 - pool in many organisms. In this study, we used a PDHC-deficient strain of Corynebacterium glutamicum, which additionally lacked pyruvate carboxylase (ΔaceE Δpyc). This strain featured a >15-h lag phase during growth on glucose-acetate mixtures. We used this strain to systematically assess the impact of alterations in the intracellular CO2/HCO3 - pool on growth in glucose-acetate medium. Remarkably, all measures enhancing CO2/HCO3 - levels successfully restored growth. These results emphasize the strong impact of the intracellular CO2/HCO3 - pool on metabolic flux, especially in strains exhibiting low endogenous CO2 production rates.
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Zeng L, Burne RA. Essential Roles of the sppRA Fructose-Phosphate Phosphohydrolase Operon in Carbohydrate Metabolism and Virulence Expression by Streptococcus mutans. J Bacteriol 2019; 201:e00586-18. [PMID: 30348833 PMCID: PMC6304665 DOI: 10.1128/jb.00586-18] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Accepted: 10/16/2018] [Indexed: 11/20/2022] Open
Abstract
The dental caries pathogen Streptococcus mutans can ferment a variety of sugars to produce organic acids. Exposure of S. mutans to certain nonmetabolizable carbohydrates, such as xylitol, impairs growth and can cause cell death. Recently, the presence of a sugar-phosphate stress in S. mutans was demonstrated using a mutant lacking 1-phosphofructokinase (FruK) that accumulates fructose-1-phosphate (F-1-P). Here, we studied an operon in S. mutans, sppRA, which was highly expressed in the fruK mutant. Biochemical characterization of a recombinant SppA protein indicated that it possessed hexose-phosphate phosphohydrolase activity, with preferences for F-1-P and, to a lesser degree, fructose-6-phosphate (F-6-P). SppA activity was stimulated by Mg2+ and Mn2+ but inhibited by NaF. SppR, a DeoR family regulator, repressed the expression of the sppRA operon to minimum levels in the absence of the fructose-derived metabolite F-1-P and likely also F-6-P. The accumulation of F-1-P, as a result of growth on fructose, not only induced sppA expression, but it significantly altered biofilm maturation through increased cell lysis and enhanced extracellular DNA release. Constitutive expression of sppA, via a plasmid or by deleting sppR, greatly alleviated fructose-induced stress in a fruK mutant, enhanced resistance to xylitol, and reversed the effects of fructose on biofilm formation. Finally, by identifying three additional putative phosphatases that are capable of promoting sugar-phosphate tolerance, we show that S. mutans is capable of mounting a sugar-phosphate stress response by modulating the levels of certain glycolytic intermediates, functions that are interconnected with the ability of the organism to manifest key virulence behaviors.IMPORTANCEStreptococcus mutans is a major etiologic agent for dental caries, primarily due to its ability to form biofilms on the tooth surface and to convert carbohydrates into organic acids. We have discovered a two-gene operon in S. mutans that regulates fructose metabolism by controlling the levels of fructose-1-phosphate, a potential signaling compound that affects bacterial behaviors. With fructose becoming increasingly common and abundant in the human diet, we reveal the ways that fructose may alter bacterial development, stress tolerance, and microbial ecology in the oral cavity to promote oral diseases.
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Affiliation(s)
- Lin Zeng
- Department of Oral Biology, University of Florida, Gainesville, Florida, USA
| | - Robert A Burne
- Department of Oral Biology, University of Florida, Gainesville, Florida, USA
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Zeng L, Chen L, Burne RA. Preferred Hexoses Influence Long-Term Memory in and Induction of Lactose Catabolism by Streptococcus mutans. Appl Environ Microbiol 2018; 84:e00864-18. [PMID: 29752268 PMCID: PMC6029091 DOI: 10.1128/aem.00864-18] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2018] [Accepted: 04/29/2018] [Indexed: 02/05/2023] Open
Abstract
Bacteria prioritize sugar metabolism via carbohydrate catabolite repression, which regulates global gene expression to optimize the catabolism of preferred substrates. Here, we report an unusual long-term memory effect in certain Streptococcus mutans strains that alters adaptation to growth on lactose after prior exposure to glucose or fructose. In strain GS-5, cells that were first cultured on fructose and then transferred to lactose displayed an exceptionally long lag (>11 h) and slower growth compared to cells first cultured on glucose or cellobiose, which displayed a reduction in lag phase by as much as 10 h. When grown on lactose, mutants lacking the cellobiose-phosphotransferase (PTS) or phospho-β-glucosidase lost the accelerated growth associated with prior culturing on glucose. The memory effects of glucose or fructose on lactose catabolism were not as profound in strain UA159, but the lag phase was considerably shorter in mutants lacking the glucose-PTS EIIMan Interestingly, when S. mutans was cultivated on lactose, significant quantities of free glucose accumulated in the medium, with higher levels found in the cultures of strains lacking EIIMan, glucokinase, or both. Free glucose was also detected in cultures that were utilizing cellobiose or trehalose, albeit at lower levels. Such release of hexoses by S. mutans is likely of biological significance as it was found that cells required small amounts of glucose or other preferred carbohydrates to initiate efficient growth on lactose. These findings suggest that S. mutans modulates the induction of lactose utilization based on its prior exposure to glucose or fructose, which can be liberated from common disaccharides.IMPORTANCE Understanding the molecular mechanisms employed by oral bacteria to control sugar metabolism is key to developing novel therapies for management of dental caries and other oral diseases. Lactose is a naturally occurring disaccharide that is abundant in dairy products and commonly ingested by humans. However, for the dental caries pathogen Streptococcus mutans, relatively little is known about the molecular mechanisms that regulate expression of genes required for lactose uptake and catabolism. Two peculiarities of lactose utilization by S. mutans are explored here: (i) S. mutans excretes glucose that it cleaves from lactose, and (ii) prior exposure to certain carbohydrates can result in a long-term inability to use lactose. The study begins to shed light on how S. mutans may utilize bet hedging to optimize its persistence and virulence in the human oral cavity.
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Affiliation(s)
- Lin Zeng
- Department of Oral Biology, University of Florida, College of Dentistry, Gainesville, Florida, USA
| | - Lulu Chen
- Department of Oral Biology, University of Florida, College of Dentistry, Gainesville, Florida, USA
- State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, Department of Pediatric Dentistry, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China
| | - Robert A Burne
- Department of Oral Biology, University of Florida, College of Dentistry, Gainesville, Florida, USA
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