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Augustiniene E, Kutraite I, Valanciene E, Matulis P, Jonuskiene I, Malys N. Transcription factor-based biosensors for detection of naturally occurring phenolic acids. N Biotechnol 2023; 78:1-12. [PMID: 37714511 DOI: 10.1016/j.nbt.2023.09.004] [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: 01/09/2023] [Revised: 06/09/2023] [Accepted: 09/12/2023] [Indexed: 09/17/2023]
Abstract
Phenolic acids including hydroxybenzoic and hydroxycinnamic acids are secondary plant and fungal metabolites involved in many physiological processes offering health and dietary benefits. They are often utilised as precursors for production of value-added compounds. The limited availability of synthetic biology tools, such as whole-cell biosensors suitable for monitoring the dynamics of phenolic acids intracellularly and extracellularly, hinders the capabilities to develop high-throughput screens to study their metabolism and forward engineering. Here, by applying a multi-genome approach, we have identified phenolic acid-inducible gene expression systems composed of transcription factor-inducible promoter pairs responding to eleven different phenolic acids. Subsequently, they were used for the development of whole-cell biosensors based on model bacterial hosts, such as Escherichia coli, Cupriavidus necator and Pseudomonas putida. The dynamics and range of the biosensors were evaluated by establishing their response and sensitivity landscapes. The specificity and previously uncharacterised interactions between transcription factor and its effector(s) were identified by a screen of twenty major phenolic acids. To exemplify applicability, we utilise a protocatechuic acid-biosensor to identify enzymes with enhanced activity for conversion of p-hydroxybenzoate to protocatechuate. Transcription factor-based biosensors developed in this study will advance the analytics of phenolic acids and expedite research into their metabolism.
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Affiliation(s)
- Ernesta Augustiniene
- Bioprocess Research Centre, Faculty of Chemical Technology, Kaunas University of Technology, Radvilenu st. 19, LT-50254 Kaunas, Lithuania
| | - Ingrida Kutraite
- Bioprocess Research Centre, Faculty of Chemical Technology, Kaunas University of Technology, Radvilenu st. 19, LT-50254 Kaunas, Lithuania
| | - Egle Valanciene
- Bioprocess Research Centre, Faculty of Chemical Technology, Kaunas University of Technology, Radvilenu st. 19, LT-50254 Kaunas, Lithuania
| | - Paulius Matulis
- Bioprocess Research Centre, Faculty of Chemical Technology, Kaunas University of Technology, Radvilenu st. 19, LT-50254 Kaunas, Lithuania
| | - Ilona Jonuskiene
- Bioprocess Research Centre, Faculty of Chemical Technology, Kaunas University of Technology, Radvilenu st. 19, LT-50254 Kaunas, Lithuania
| | - Naglis Malys
- Bioprocess Research Centre, Faculty of Chemical Technology, Kaunas University of Technology, Radvilenu st. 19, LT-50254 Kaunas, Lithuania; Department of Organic Chemistry, Faculty of Chemical Technology, Kaunas University of Technology, Radvilenu st. 19, LT-50254 Kaunas, Lithuania.
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Ke Z, Zhu Q, Zhang M, Gao S, jiang M, Zhou Y, Qiu J, Cheng M, Yan X, Wang J, Hong Q. Unveiling the regulatory mechanisms of salicylate degradation gene cluster cehGHIR4 in Rhizobium sp. strain X9. Appl Environ Microbiol 2023; 89:e0080223. [PMID: 37800922 PMCID: PMC10617420 DOI: 10.1128/aem.00802-23] [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: 05/15/2023] [Accepted: 07/19/2023] [Indexed: 10/07/2023] Open
Abstract
In a previous study, the novel gene cluster cehGHI was found to be involved in salicylate degradation through the CoA-mediated pathway in Rhizobium sp. strain X9 (Mol Microbiol 116:783-793, 2021). In this study, an IclR family transcriptional regulator CehR4 was identified. In contrast to other regulators involved in salicylate degradation, cehR4 forms one operon with the gentisyl-CoA thioesterase gene cehI, while cehG and cehH (encoding salicylyl-CoA ligase and salicylyl-CoA hydroxylase, respectively) form another operon. cehGH and cehIR4 are divergently transcribed, and their promoters overlap. The results of the electrophoretic mobility shift assay and DNase I footprinting showed that CehR4 binds to the 42-bp motif between genes cehH and cehI, thus regulating transcription of cehGH and cehIR4. The repeat sequences IR1 (5'-TTTATATAAA-3') and IR2 (5'-AATATAGAAA-3') in the motif are key sites for CehR4 binding. The arrangement of cehGH and cehIR4 and the conserved binding motif of CehR4 were also found in other bacterial genera. The results disclose the regulatory mechanism of salicylate degradation through the CoA pathway and expand knowledge about the systems controlled by IclR family transcriptional regulators.IMPORTANCEThe long-term residue of aromatic compounds in the environment has brought great threat to the environment and human health. Microbial degradation plays an important role in the elimination of aromatic compounds in the environment. Salicylate is a common intermediate metabolite in the degradation of various aromatic compounds. Recently, Rhizobium sp. strain X9, capable of degrading the pesticide carbaryl, was isolated from carbaryl-contaminated soil. Salicylate is the intermediate metabolite that appeared during the degradation of carbaryl, and a novel salicylate degradation pathway and the involved gene cluster cehGHIR4 have been identified. This study identified and characterized the IclR transcription regulator CehR4 that represses transcription of cehGHIR4 gene cluster. Additionally, the genetic arrangements of cehGH and cehIR4 and the binding sites of CehR4 were also found in other bacterial genera. This study provides insights into the biodegradation of salicylate and provides an application in the bioremediation of aromatic compound-contaminated environments.
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Affiliation(s)
- Zhijian Ke
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, China
- School of Biological and Chemical Engineering, Ningbo Tech University, Ningbo, Zhejiang, China
| | - Qian Zhu
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, China
| | - Mingliang Zhang
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, China
| | - Siyuan Gao
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, China
| | - Mingli jiang
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, China
| | - Yidong Zhou
- School of Life Sciences, Nantong University, Nantong, Jiangsu, China
| | - Jiguo Qiu
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, China
| | - Minggen Cheng
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, China
| | - Xin Yan
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, China
| | - Jinbo Wang
- School of Biological and Chemical Engineering, Ningbo Tech University, Ningbo, Zhejiang, China
| | - Qing Hong
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, China
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Sun S, Wang Y, Xu C, Qiao C, Chen S, Zhao C, Liu Q, Zhang X. Reconstruction of microbiome and functionality accelerated crude oil biodegradation of 2,4-DCP-oil-contaminated soil systems using composite microbial agent B-Cl. JOURNAL OF HAZARDOUS MATERIALS 2023; 447:130808. [PMID: 36669400 DOI: 10.1016/j.jhazmat.2023.130808] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Revised: 01/02/2023] [Accepted: 01/15/2023] [Indexed: 06/17/2023]
Abstract
Biodegradation is one of the safest and most economical methods for the elimination of toxic chlorophenols and crude oil from the environment. In this study, aerobic degradation of the aforementioned compounds by composite microbial agent B-Cl, which consisted of Bacillus B1 and B2 in a 3:2 ratio, was analyzed. The biodegradation mechanism of B-Cl was assessed based on whole genome sequencing, Fourier transform infrared spectroscopy and gas chromatographic analyses. B-Cl was most effective at reducing Cl- concentrations (65.17%) and crude oil biodegradation (59.18%) at 7 d, which was when the content of alkanes ≤ C30 showed the greatest decrease. Furthermore, adding B-Cl solution to soil significantly decreased the 2,4-DCP and oil content to below the detection limit and by 80.68%, respectively, and reconstructed of the soil microbial into a system containing more CPs-degrading (exaA, frmA, L-2-HAD, dehH, ALDH, catABE), aromatic compounds-degrading (pcaGH, catAE, benA-xylX, paaHF) and alkane- and fatty acid-degrading (alkB, atoB, fadANJ) microorganisms. Moreover, the presence of 2,4-DCP was the main hinder of the observed effects. This study demonstrates the importance of adding B-Cl solution to determine the interplay of CPs with microbes and accelerating oil degradation, which can be used for in-situ bioremediation of CPs and oil-contaminated soil.
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Affiliation(s)
- Shuo Sun
- College of Chemistry and Chemical Engineering, China University of Petroleum (East China), Qingdao 266580, PR China; State Key Laboratory of Petroleum Pollution Control, Qingdao 266580, PR China
| | - Yaru Wang
- College of Chemistry and Chemical Engineering, China University of Petroleum (East China), Qingdao 266580, PR China; State Key Laboratory of Petroleum Pollution Control, Qingdao 266580, PR China
| | - Chenfei Xu
- College of Chemistry and Chemical Engineering, China University of Petroleum (East China), Qingdao 266580, PR China; State Key Laboratory of Petroleum Pollution Control, Qingdao 266580, PR China
| | - Chenlu Qiao
- College of Chemistry and Chemical Engineering, China University of Petroleum (East China), Qingdao 266580, PR China; State Key Laboratory of Petroleum Pollution Control, Qingdao 266580, PR China
| | - Shuiquan Chen
- College of Energy and Mining Engineering, Shandong University of Science and Technology, Qingdao 266590, PR China
| | - Chaocheng Zhao
- College of Chemistry and Chemical Engineering, China University of Petroleum (East China), Qingdao 266580, PR China; State Key Laboratory of Petroleum Pollution Control, Qingdao 266580, PR China
| | - Qiyou Liu
- College of Chemistry and Chemical Engineering, China University of Petroleum (East China), Qingdao 266580, PR China; State Key Laboratory of Petroleum Pollution Control, Qingdao 266580, PR China.
| | - Xiuxia Zhang
- College of Chemistry and Chemical Engineering, China University of Petroleum (East China), Qingdao 266580, PR China; State Key Laboratory of Petroleum Pollution Control, Qingdao 266580, PR China
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Xu SQ, Wang X, Xu L, Wang KX, Jiang YH, Zhang FY, Hong Q, He J, Liu SJ, Qiu JG. The MocR family transcriptional regulator DnfR has multiple binding sites and regulates Dirammox gene transcription in Alcaligenes faecalis JQ135. Environ Microbiol 2023; 25:675-688. [PMID: 36527381 DOI: 10.1111/1462-2920.16318] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Accepted: 12/14/2022] [Indexed: 12/23/2022]
Abstract
Microbial ammonia oxidation is vital to the nitrogen cycle. A biological process, called Dirammox (direct ammonia oxidation, NH3 →NH2 OH→N2 ), has been recently identified in Alcaligenes ammonioxydans and Alcaligenes faecalis. However, its transcriptional regulatory mechanism has not yet been fully elucidated. The present study characterized a new MocR-like transcription factor DnfR that is involved in the Dirammox process in A. faecalis strain JQ135. The entire dnf cluster was composed of 10 genes and transcribed as five transcriptional units, that is, dnfIH, dnfR, dnfG, dnfABCDE and dnfF. DnfR activates the transcription of dnfIH, dnfG and dnfABCDE genes, and represses its own transcription. The intact 1506-bp dnfR gene was required for activation of Dirammox. Electrophoretic mobility shift assays and DNase I footprinting analyses showed that DnfR has one binding site in the dnfH-dnfR intergenic region and two binding sites in the dnfG-dnfA intergenic region. Three binding sites of DnfR shared a 6-bp repeated conserved sequence 5'-GGTCTG-N17 -GGTCTG-3' which was essential for the transcription of downstream target genes. Cysteine and glutamate act as possible effectors of DnfR to activate the transcription of transcriptional units of dnfG and dnfABCDE, respectively. This study provided new insights in the transcriptional regulation mechanism of Dirammox by DnfR in A. faecalis JQ135.
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Affiliation(s)
- Si-Qiong Xu
- Key Laboratory of Agricultural and Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, China
| | - Xiao Wang
- Key Laboratory of Agricultural and Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, China
| | - Lu Xu
- Key Laboratory of Agricultural and Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, China
| | - Ke-Xin Wang
- Key Laboratory of Agricultural and Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, China
| | - Yin-Hu Jiang
- Key Laboratory of Agricultural and Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, China
| | - Fu-Yin Zhang
- Key Laboratory of Agricultural and Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, China
| | - Qing Hong
- Key Laboratory of Agricultural and Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, China
| | - Jian He
- Key Laboratory of Agricultural and Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, China
| | - Shuang-Jiang Liu
- State Key Laboratory of Microbial Resources, and Environmental Microbiology Research Center at Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China
| | - Ji-Guo Qiu
- Key Laboratory of Agricultural and Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing, China
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The structure-function relationship of bacterial transcriptional regulators as a target for enhanced biodegradation of aromatic hydrocarbons. Microbiol Res 2022; 262:127087. [DOI: 10.1016/j.micres.2022.127087] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2022] [Revised: 06/03/2022] [Accepted: 06/03/2022] [Indexed: 11/20/2022]
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Two LysR family transcriptional regulators, McbH and McbN, activate the operons responsible for the midstream and downstream pathways of carbaryl degradation in Pseudomonas sp. strain XWY-1, respectively. Appl Environ Microbiol 2021; 88:e0206021. [PMID: 34936841 DOI: 10.1128/aem.02060-21] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Previously, a LysR family transcriptional regulator McbG that activates the mcbBCDEF gene cluster involved in the upstream pathway (from carbaryl to salicylate) of carbaryl degradation in Pseudomonas sp. strain XWY-1 has been identified by us (Appl. Environ. Microbiol. 2021, 87(9): e02970-20.). In this study, we identified McbH and McbN, which activate mcbIJKLM cluster (responsible for the midstream pathway, from salicylate to gentisate) and mcbOPQ cluster (responsible for the downstream pathway, from gentisate to pyruvate and fumarate), respectively. They both belong to the LysR family of transcriptional regulators. Gene disruption and complementation study reveal that McbH is essential for transcription of the mcbIJKLM cluster in response to salicylate and McbN is indispensable for the transcription of the mcbOPQ cluster in response to gentisate. The results of electrophoretic mobility shift assay (EMSA) and DNase I footprinting showed that McbH binds to the 52-bp motif in the mcbIJKLM promoter area and McbN binds to the 58-bp motif in the mcbOPQ promoter area. The key sequence of McbH binding to mcbIJKLM promoter is a 13-bp motif that conforms to the typical characteristics of LysR family. However, the 12-bp motif that is different from the typical characteristics of the LysR family regulator binding site sequence is identified as the key sequence for McbN to bind to the mcbOPQ promoter. This study reveals the regulatory mechanism for the midstream and downstream pathway of carbaryl degradation in strain XWY-1 and further enriches the members of the LysR transcription regulator family. IMPORTANCE: The enzyme-encoding genes involved in the complete degradation pathway of carbaryl in Pseudomonas sp. strain XWY-1 include mcbABCDEF, mcbIJKLM and mcbOPQ. Previous studies demonstrated that the mcbA gene responsible for hydrolysis of carbaryl to 1-naphthol is constitutively expressed and the transcription of mcbBCDEF was regulated by McbG. However, the transcription regulation mechanisms of mcbIJKLM and mcbOPQ have not been investigated yet. In this study, we identified two LysR-type transcriptional regulators, McbH and McbN, which activate the mcbIJKLM cluster responsible for the degradation of salicylate to gentisate and mcbOPQ cluster responsible for the degradation of gentisate to pyruvate and fumarate, respectively. The 13-bp motif is critical for McbH to bind to the promoter of mcbIJKLM, and 12-bp motif different from the typical characteristics of the LTTR binding sequence affects the binding of McbN to promoter. These findings help to expand the understanding of the regulatory mechanism of microbial degradation of carbaryl.
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Suvorova IA, Gelfand MS. Comparative Analysis of the IclR-Family of Bacterial Transcription Factors and Their DNA-Binding Motifs: Structure, Positioning, Co-Evolution, Regulon Content. Front Microbiol 2021; 12:675815. [PMID: 34177859 PMCID: PMC8222616 DOI: 10.3389/fmicb.2021.675815] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2021] [Accepted: 05/14/2021] [Indexed: 11/13/2022] Open
Abstract
The IclR-family is a large group of transcription factors (TFs) regulating various biological processes in diverse bacteria. Using comparative genomics techniques, we have identified binding motifs of IclR-family TFs, reconstructed regulons and analyzed their content, finding co-occurrences between the regulated COGs (clusters of orthologous genes), useful for future functional characterizations of TFs and their regulated genes. We describe two main types of IclR-family motifs, similar in sequence but different in the arrangement of the half-sites (boxes), with GKTYCRYW3-4RYGRAMC and TGRAACAN1-2TGTTYCA consensuses, and also predict that TFs in 32 orthologous groups have binding sites comprised of three boxes with alternating direction, which implies two possible alternative modes of dimerization of TFs. We identified trends in site positioning relative to the translational gene start, and show that TFs in 94 orthologous groups bind tandem sites with 18-22 nucleotides between their centers. We predict protein-DNA contacts via the correlation analysis of nucleotides in binding sites and amino acids of the DNA-binding domain of TFs, and show that the majority of interacting positions and predicted contacts are similar for both types of motifs and conform well both to available experimental data and to general protein-DNA interaction trends.
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Affiliation(s)
- Inna A Suvorova
- Institute for Information Transmission Problems of Russian Academy of Sciences (The Kharkevich Institute), Moscow, Russia
| | - Mikhail S Gelfand
- Institute for Information Transmission Problems of Russian Academy of Sciences (The Kharkevich Institute), Moscow, Russia.,Skolkovo Institute of Science and Technology, Moscow, Russia
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Physiological Response of Corynebacterium glutamicum to Indole. Microorganisms 2020; 8:microorganisms8121945. [PMID: 33302489 PMCID: PMC7764795 DOI: 10.3390/microorganisms8121945] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Revised: 12/04/2020] [Accepted: 12/05/2020] [Indexed: 12/20/2022] Open
Abstract
The aromatic heterocyclic compound indole is widely spread in nature. Due to its floral odor indole finds application in dairy, flavor, and fragrance products. Indole is an inter- and intracellular signaling molecule influencing cell division, sporulation, or virulence in some bacteria that synthesize it from tryptophan by tryptophanase. Corynebacterium glutamicum that is used for the industrial production of amino acids including tryptophan lacks tryptophanase. To test if indole is metabolized by C. glutamicum or has a regulatory role, the physiological response to indole by this bacterium was studied. As shown by RNAseq analysis, indole, which inhibited growth at low concentrations, increased expression of genes involved in the metabolism of iron, copper, and aromatic compounds. In part, this may be due to iron reduction as indole was shown to reduce Fe3+ to Fe2+ in the culture medium. Mutants with improved tolerance to indole were selected by adaptive laboratory evolution. Among the mutations identified by genome sequencing, mutations in three transcriptional regulator genes were demonstrated to be causal for increased indole tolerance. These code for the regulator of iron homeostasis DtxR, the regulator of oxidative stress response RosR, and the hitherto uncharacterized Cg3388. Gel mobility shift analysis revealed that Cg3388 binds to the intergenic region between its own gene and the iolT2-rhcM2D2 operon encoding inositol uptake system IolT2, maleylacetate reductase, and catechol 1,2-dioxygenase. Increased RNA levels of rhcM2 in a cg3388 deletion strain indicated that Cg3388 acts as repressor. Indole, hydroquinone, and 1,2,4-trihydroxybenzene may function as inducers of the iolT2-rhcM2D2 operon in vivo as they interfered with DNA binding of Cg3388 at physiological concentrations in vitro. Cg3388 was named IhtR.
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The Syringate O-Demethylase Gene of Sphingobium sp. Strain SYK-6 Is Regulated by DesX, while Other Vanillate and Syringate Catabolism Genes Are Regulated by DesR. Appl Environ Microbiol 2020; 86:AEM.01712-20. [PMID: 32917754 DOI: 10.1128/aem.01712-20] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2020] [Accepted: 09/02/2020] [Indexed: 12/26/2022] Open
Abstract
Syringate and vanillate are the major metabolites of lignin biodegradation. In Sphingobium sp. strain SYK-6, syringate is O demethylated to gallate by consecutive reactions catalyzed by DesA and LigM, and vanillate is O demethylated to protocatechuate by a reaction catalyzed by LigM. The gallate ring is cleaved by DesB, and protocatechuate is catabolized via the protocatechuate 4,5-cleavage pathway. The transcriptions of desA, ligM, and desB are induced by syringate and vanillate, while those of ligM and desB are negatively regulated by the MarR-type transcriptional regulator DesR, which is not involved in desA regulation. Here, we clarified the regulatory system for desA transcription by analyzing the IclR-type transcriptional regulator desX, located downstream of desA Quantitative reverse transcription (RT)-PCR analyses of a desX mutant indicated that the transcription of desA was negatively regulated by DesX. In contrast, DesX was not involved in the regulation of ligM and desB The ferulate catabolism genes (ferBA), under the control of a MarR-type transcriptional regulator, FerC, are located upstream of desA RT-PCR analyses suggested that the ferB-ferA-SLG_25010-desA gene cluster consists of the ferBA operon and the SLG_25010-desA operon. Promoter assays revealed that a syringate- and vanillate-inducible promoter is located upstream of SLG_25010. Purified DesX bound to this promoter region, which overlaps an 18-bp inverted-repeat sequence that appears to be essential for the DNA binding of DesX. Syringate and vanillate inhibited the DNA binding of DesX, indicating that the compounds are effector molecules of DesX.IMPORTANCE Syringate is a major degradation product in the microbial and chemical degradation of syringyl lignin. Along with other low-molecular-weight aromatic compounds, syringate is produced by chemical lignin depolymerization. Converting this mixture into value-added chemicals using bacterial metabolism (i.e., biological funneling) is a promising option for lignin valorization. To construct an efficient microbial lignin conversion system, it is necessary to identify and characterize the genes involved in the uptake and catabolism of lignin-derived aromatic compounds and to elucidate their transcriptional regulation. In this study, we found that the transcription of desA, encoding syringate O-demethylase in SYK-6, is regulated by an IclR-type transcriptional regulator, DesX. The findings of this study, combined with our previous results on desR (encoding a MarR transcriptional regulator that controls the transcription of ligM and desB), provide an overall picture of the transcriptional-regulatory systems for syringate and vanillate catabolism in SYK-6.
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Cheng M, Xing Z, Lu L, Chen F, He J, Huang X. A plasmid-based genomic screening system for transcriptional regulators of non-adjacent xenobiotic catabolism genes. Appl Microbiol Biotechnol 2019; 104:1163-1174. [PMID: 31822983 DOI: 10.1007/s00253-019-10268-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Revised: 11/11/2019] [Accepted: 11/22/2019] [Indexed: 12/01/2022]
Abstract
Bacteria play an important role in the catabolism of environmental xenobiotics. The study of transcriptional regulation has greatly enhanced our understanding of the molecular mechanisms associated with these processes. However, genes encoding transcription factors (TFs) for xenobiotic catabolism are usually not located in the immediate vicinity of the catabolic genes that they regulate; therefore, functional identification of these TFs is difficult. Significantly modified from a metagenome screening method substrate-induced gene expression (SIGEX), here we propose a synthetic pSRGFP-18 plasmid-based tool as a TF reporter system. In short, two multiple cloning sites (MCS) were designed; one in front of an egfp reporter gene was constructed for promoter insertion, and the other MCS was used for shotgun cloning of genomic DNA. Based on the regulatory relationship between TFs and the promoter of their associated catabolic genes, this approach allowed us to screen for TF genes using a genome shotgun approach. This system performed well when testing the known operons. Following statistical analysis of known catabolic operons in Escherichia coli and Bacillus subtilis, the suggested region of the target promoter for this system was from - 250 to + 150. Furthermore, to broaden the applicability of this plasmid, a series of pSRGFP-18 and pBBR1-based pSRGFP-X plasmids were constructed, which had broad host ranges and contained different antibiotic markers. This study outlines a powerful tool to enable functional identification of TFs for bacterial xenobiotic catabolism.
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Affiliation(s)
- Minggen Cheng
- College of Life Sciences, Nanjing Agricultural University, Nanjing, 210095, Jiangsu, China
| | - Ziyu Xing
- College of Life Sciences, Nanjing Agricultural University, Nanjing, 210095, Jiangsu, China
| | - Luyao Lu
- College of Life Sciences, Nanjing Agricultural University, Nanjing, 210095, Jiangsu, China
| | - Feng Chen
- College of Life Sciences, Nanjing Agricultural University, Nanjing, 210095, Jiangsu, China
| | - Jian He
- College of Life Sciences, Nanjing Agricultural University, Nanjing, 210095, Jiangsu, China
| | - Xing Huang
- College of Life Sciences, Nanjing Agricultural University, Nanjing, 210095, Jiangsu, China.
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Raymond-Bouchard I, Tremblay J, Altshuler I, Greer CW, Whyte LG. Comparative Transcriptomics of Cold Growth and Adaptive Features of a Eury- and Steno-Psychrophile. Front Microbiol 2018; 9:1565. [PMID: 30108551 PMCID: PMC6080646 DOI: 10.3389/fmicb.2018.01565] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Accepted: 06/25/2018] [Indexed: 12/12/2022] Open
Abstract
Permafrost subzero environments harbor diverse, active communities of microorganisms. However, our understanding of the subzero growth, metabolisms, and adaptive properties of these microbes remains very limited. We performed transcriptomic analyses on two subzero-growing permafrost isolates with different growth profiles in order to characterize and compare their cold temperature growth and cold-adaptive strategies. The two organisms, Rhodococcus sp. JG3 (-5 to 30°C) and Polaromonas sp. Eur3 1.2.1 (-5 to 22°C), shared several common responses during low temperature growth, including induction of translation and ribosomal processes, upregulation of nutrient transport, increased oxidative and osmotic stress responses, and stimulation of polysaccharide capsule synthesis. Recombination appeared to be an important adaptive strategy for both isolates at low temperatures, likely as a mechanism to increase genetic diversity and the potential for survival in cold systems. While Rhodococcus sp. JG3 favored upregulating iron and amino acid transport, sustaining redox potential, and modulating fatty acid synthesis and composition during growth at -5°C compared to 25°C, Polaromonas sp. Eur3 1.2.1 increased the relative abundance of transcripts involved in primary energy metabolism and the electron transport chain, in addition to signal transduction and peptidoglycan synthesis at 0°C compared to 20°C. The increase in energy metabolism may explain why Polaromonas sp. Eur3 1.2.1 is able to sustain growth rates at 0°C comparable to those at higher temperatures. For Rhodococcus sp. JG3, flexibility in use of carbon sources, iron acquisition, control of membrane fatty acid composition, and modulating redox and co-factor potential may be ways in which this organism is able to sustain growth over a wider range of temperatures. Increasing our understanding of the microbes in these habitats helps us better understand active pathways and metabolisms in extreme environments. Identifying novel, thermolabile, and cold-active enzymes from studies such as this is also of great interest to the biotechnology and food industries.
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Affiliation(s)
| | - Julien Tremblay
- Biotechnology Research Institute, National Research Council of Canada, Montreal, QC, Canada
| | - Ianina Altshuler
- Department of Natural Resource Sciences, McGill University, Sainte-Anne-de-Bellevue, QC, Canada
| | - Charles W Greer
- Biotechnology Research Institute, National Research Council of Canada, Montreal, QC, Canada
| | - Lyle G Whyte
- Department of Natural Resource Sciences, McGill University, Sainte-Anne-de-Bellevue, QC, Canada
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12
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Herrou J, Czyż DM, Fiebig A, Willett JW, Kim Y, Wu R, Babnigg G, Crosson S. Molecular control of gene expression by Brucella BaaR, an IclR-type transcriptional repressor. J Biol Chem 2018; 293:7437-7456. [PMID: 29567835 DOI: 10.1074/jbc.ra118.002045] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Revised: 03/19/2018] [Indexed: 01/06/2023] Open
Abstract
The general stress response sigma factor σE1 directly and indirectly regulates the transcription of dozens of genes that influence stress survival and host infection in the zoonotic pathogen Brucella abortus Characterizing the functions of σE1-regulated genes therefore would contribute to our understanding of B. abortus physiology and infection biology. σE1 indirectly activates transcription of the IclR family regulator Bab2_0215, but the function of this regulator remains undefined. Here, we present a structural and functional characterization of Bab2_0215, which we have named B rucella adipic acid-activated regulator (BaaR). We found that BaaR adopts a classic IclR-family fold and directly represses the transcription of two operons with predicted roles in carboxylic acid oxidation. BaaR binds two sites on chromosome II between baaR and a divergently transcribed hydratase/dehydrogenase (acaD2), and it represses transcription of both genes. We identified three carboxylic acids (adipic acid, tetradecanedioic acid, and ϵ-aminocaproic acid) and a lactone (ϵ-caprolactone) that enhance transcription from the baaR and acaD2 promoters. However, neither the activating acids nor caprolactone enhanced transcription by binding directly to BaaR. Induction of baaR transcription by adipic acid required the gene bab2_0213, which encodes a major facilitator superfamily transporter, suggesting that Bab2_0213 transports adipic acid across the inner membrane. We conclude that a suite of structurally related organic molecules activate transcription of genes repressed by BaaR. Our study provides molecular-level understanding of a gene expression program in B. abortus that is downstream of σE1.
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Affiliation(s)
- Julien Herrou
- Departments of Biochemistry and Molecular Biology, Chicago, Illinois 60637; Howard Taylor Ricketts Laboratory, University of Chicago, Argonne, Illinois 60439
| | - Daniel M Czyż
- Departments of Biochemistry and Molecular Biology, Chicago, Illinois 60637; Howard Taylor Ricketts Laboratory, University of Chicago, Argonne, Illinois 60439
| | - Aretha Fiebig
- Howard Taylor Ricketts Laboratory, University of Chicago, Argonne, Illinois 60439
| | - Jonathan W Willett
- Departments of Biochemistry and Molecular Biology, Chicago, Illinois 60637; Howard Taylor Ricketts Laboratory, University of Chicago, Argonne, Illinois 60439
| | | | - Ruiying Wu
- Argonne National Laboratory, Argonne, Illinois 60439
| | | | - Sean Crosson
- Departments of Biochemistry and Molecular Biology, Chicago, Illinois 60637; Howard Taylor Ricketts Laboratory, University of Chicago, Argonne, Illinois 60439; Microbiology, University of Chicago, Chicago, Illinois 60637.
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13
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Wang JP, Zhang WM, Chao HJ, Zhou NY. PnpM, a LysR-Type Transcriptional Regulator Activates the Hydroquinone Pathway in para-Nitrophenol Degradation in Pseudomonas sp. Strain WBC-3. Front Microbiol 2017; 8:1714. [PMID: 28959240 PMCID: PMC5603801 DOI: 10.3389/fmicb.2017.01714] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Accepted: 08/24/2017] [Indexed: 11/17/2022] Open
Abstract
A LysR-type transcriptional regulator (LTTR), PnpR, has previously been shown to activate the transcription of operons pnpA, pnpB, and pnpCDEFG for para-nitrophenol (PNP) degradation in Pseudomonas sp. strain WBC-3. Further preliminary evidence suggested the possible presence of an LTTR additional binding site in the promoter region of pnpCDEFG. In this study, an additional LTTR PnpM, which shows 44% homology to PnpR, was determined to activate the expression of pnpCDEFG. Interestingly, a pnpM-deleted WBC-3 strain was unable to grow on PNP but accumulating hydroquinone (HQ), which is the catabolic product from PNP degradation by PnpAB and the substrate for PnpCD. Through electrophoretic mobility shift assays (EMSAs) and promoter activity detection, only PnpR was involved in the activation of pnpA and pnpB, but both PnpR and PnpM were involved in the activation of pnpCDEFG. DNase I footprinting analysis suggested that PnpR and PnpM shared the same DNA-binding regions of 27 bp in the pnpCDEFG promoter. In the presence of PNP, the protection region increased to 39 bp by PnpR and to 38 bp by PnpM. Our data suggested that both PnpR and PnpM were involved in activating pnpCDEFG expression, in which PNP rather than the substrate hydroquinone for PnpCD is the inducer. Thus, during the PNP catabolism in Pseudomonas sp. strain WBC-3, pnpA and pnpB operons for the initial two reactions were controlled by PnpR, while the third operon (pnpCDEFG) for HQ degradation was activated by PnpM and PnpR. This study builds upon our previous findings and shows that two LTTRs PnpR and PnpM are involved in the transcriptional activation of these three catabolic operons. Specifically, our identification that an LTTR, PnpM, regulates pnpCDEFG expression provides new insights in an intriguing regulation system of PNP catabolism that is controlled by two regulators.
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Affiliation(s)
- Jin-Pei Wang
- Wuhan Institute of Virology, Chinese Academy of SciencesWuhan, China.,University of Chinese Academy of SciencesBeijing, China
| | - Wen-Mao Zhang
- Wuhan Institute of Virology, Chinese Academy of SciencesWuhan, China
| | - Hong-Jun Chao
- Wuhan Institute of Virology, Chinese Academy of SciencesWuhan, China
| | - Ning-Yi Zhou
- Wuhan Institute of Virology, Chinese Academy of SciencesWuhan, China.,State Key Laboratory of Microbial Metabolism and School of Life Sciences & Biotechnology, Shanghai Jiao Tong UniversityShanghai, China
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14
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Biotechnological production of aromatic compounds of the extended shikimate pathway from renewable biomass. J Biotechnol 2017; 257:211-221. [DOI: 10.1016/j.jbiotec.2016.11.016] [Citation(s) in RCA: 75] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2016] [Revised: 11/17/2016] [Accepted: 11/17/2016] [Indexed: 01/17/2023]
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15
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A functional 4-hydroxybenzoate degradation pathway in the phytopathogen Xanthomonas campestris is required for full pathogenicity. Sci Rep 2015; 5:18456. [PMID: 26672484 PMCID: PMC4682078 DOI: 10.1038/srep18456] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2015] [Accepted: 11/17/2015] [Indexed: 11/23/2022] Open
Abstract
Plants contain significant levels of natural phenolic compounds essential for reproduction and growth, as well as defense mechanisms against pathogens. Xanthomonas campestris pv. campestris (Xcc) is the causal agent of crucifers black rot. Here we showed that genes required for the synthesis, utilization, transportation, and degradation of 4-hydroxybenzoate (4-HBA) are present in Xcc. Xcc rapidly degrades 4-HBA, but has no effect on 2-hydroxybenzoate and 3-hydroxybenzoate when grown in XOLN medium. The genes for 4-HBA degradation are organized in a superoperonic cluster. Bioinformatics, biochemical, and genetic data showed that 4-HBA is hydroxylated by 4-HBA 3-hydroxylase (PobA), which is encoded by Xcc0356, to yield PCA. The resulting PCA is further metabolized via the PCA branches of the β-ketoadipate pathway, including Xcc0364, Xcc0365, and PcaFHGBDCR. Xcc0364 and Xcc0365 encode a new form of β-ketoadipate succinyl-coenzyme A transferase that is required for 4-HBA degradation. pobA expression was induced by 4-HBA via the transcriptional activator, PobR. Radish and cabbage hydrolysates contain 2-HBA, 3-HBA, 4-HBA, and other phenolic compounds. Addition of radish and cabbage hydrolysates to Xcc culture significantly induced the expression of pobA via PobR. The 4-HBA degradation pathway is required for full pathogenicity of Xcc in radish.
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16
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A Two-Component para-Nitrophenol Monooxygenase Initiates a Novel 2-Chloro-4-Nitrophenol Catabolism Pathway in Rhodococcus imtechensis RKJ300. Appl Environ Microbiol 2015; 82:714-23. [PMID: 26567304 DOI: 10.1128/aem.03042-15] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2015] [Accepted: 11/09/2015] [Indexed: 11/20/2022] Open
Abstract
Rhodococcus imtechensis RKJ300 (DSM 45091) grows on 2-chloro-4-nitrophenol (2C4NP) and para-nitrophenol (PNP) as the sole carbon and nitrogen sources. In this study, by genetic and biochemical analyses, a novel 2C4NP catabolic pathway different from those of all other 2C4NP utilizers was identified with hydroxyquinol (hydroxy-1,4-hydroquinone or 1,2,4-benzenetriol [BT]) as the ring cleavage substrate. Real-time quantitative PCR analysis indicated that the pnp cluster located in three operons is likely involved in the catabolism of both 2C4NP and PNP. The oxygenase component (PnpA1) and reductase component (PnpA2) of the two-component PNP monooxygenase were expressed and purified to homogeneity, respectively. The identification of chlorohydroquinone (CHQ) and BT during 2C4NP degradation catalyzed by PnpA1A2 indicated that PnpA1A2 catalyzes the sequential denitration and dechlorination of 2C4NP to BT and catalyzes the conversion of PNP to BT. Genetic analyses revealed that pnpA1 plays an essential role in both 2C4NP and PNP degradations by gene knockout and complementation. In addition to catalyzing the oxidation of CHQ to BT, PnpA1A2 was also found to be able to catalyze the hydroxylation of hydroquinone (HQ) to BT, revealing the probable fate of HQ that remains unclear in PNP catabolism by Gram-positive bacteria. This study fills a gap in our knowledge of the 2C4NP degradation mechanism in Gram-positive bacteria and also enhances our understanding of the genetic and biochemical diversity of 2C4NP catabolism.
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17
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Toyoda K, Inui M. Regulons of global transcription factors in Corynebacterium glutamicum. Appl Microbiol Biotechnol 2015; 100:45-60. [DOI: 10.1007/s00253-015-7074-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2015] [Revised: 10/03/2015] [Accepted: 10/07/2015] [Indexed: 10/22/2022]
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18
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PbaR, an IclR family transcriptional activator for the regulation of the 3-phenoxybenzoate 1',2'-dioxygenase gene cluster in Sphingobium wenxiniae JZ-1T. Appl Environ Microbiol 2015; 81:8084-92. [PMID: 26386050 DOI: 10.1128/aem.02122-15] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2015] [Accepted: 09/10/2015] [Indexed: 11/20/2022] Open
Abstract
The 3-phenoxybenzoate (3-PBA) 1',2'-dioxygenase gene cluster (pbaA1A2B cluster), which is responsible for catalyzing 3-phenoxybenzoate to 3-hydroxybenzoate and catechol, is inducibly expressed in Sphingobium wenxiniae strain JZ-1(T) by its substrate 3-PBA. In this study, we identified a transcriptional activator of the pbaA1A2B cluster, PbaR, using a DNA affinity approach. PbaR is a 253-amino-acid protein with a molecular mass of 28,000 Da. PbaR belongs to the IclR family of transcriptional regulators and shows 99% identity to a putative transcriptional regulator that is located on the carbazole-degrading plasmid pCAR3 in Sphingomonas sp. strain KA1. Gene disruption and complementation showed that PbaR was essential for transcription of the pbaA1A2B cluster in response to 3-PBA in strain JZ-1(T). However, PbaR does not regulate the reductase component gene pbaC. An electrophoretic mobility shift assay and DNase I footprinting showed that PbaR binds specifically to the 29-bp motif AATAGAAAGTCTGCCGTACGGCTATTTTT in the pbaA1A2B promoter area and that the palindromic sequence (GCCGTACGGC) within the motif is essential for PbaR binding. The binding site was located between the -10 box and the ribosome-binding site (downstream of the transcriptional start site), which is distinct from the location of the binding site in previously reported IclR family transcriptional regulators. This study reveals the regulatory mechanism for 3-PBA degradation in strain JZ-1(T), and the identification of PbaR increases the variety of regulatory models in the IclR family of transcriptional regulators.
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19
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Involvement of the global regulator GlxR in 3-hydroxybenzoate and gentisate utilization by Corynebacterium glutamicum. Appl Environ Microbiol 2014; 80:4215-25. [PMID: 24795375 DOI: 10.1128/aem.00290-14] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Corynebacterium glutamicum is an industrially important producer of amino acids and organic acids, as well as an emerging model system for aromatic assimilation. An IclR-type regulator GenR has been characterized to activate the transcription of genDFM and genKH operons for 3-hydroxybenzoate and gentisate catabolism and represses its own expression. On the other hand, GlxR, a global regulator of the cyclic AMP (cAMP) receptor protein-fumarate nitrate reductase regulator (CRP-FNR) type, was also predicted to be involved in this pathway. In this study, electrophoretic mobility shift assays and footprinting analyses demonstrated that GlxR bound to three sites in the promoter regions of three gen operons. A combination of site-directed mutagenesis of the biding sites, promoter activity assay, and GlxR overexpression demonstrated that GlxR repressed their expression by binding these sites. One GlxR binding site (DFMx) was found to be located -13 to +8 bp upstream of the genDFM promoter, which was involved in negative regulation of genDFM transcription. The GlxR binding site R-KHx01 (located between positions -11 to +5) was upstream of the genKH promoter sequence and involved in negative regulation of its transcription. The binding site R-KHx02, at which GlxR binds to genR promoter to repress its expression, was found within a footprint extending from positions -71 to -91 bp. These results reveal that GlxR represses the transcription of all three gen operons and then contributes to the synchronization of their expression for 3-hydroxybenzoate and gentisate catabolism in collaboration with the specific regulator GenR.
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Characterization of LgnR, an IclR family transcriptional regulator involved in the regulation of l-gluconate catabolic genes in Paracoccus sp. 43P. Microbiology (Reading) 2014; 160:623-634. [DOI: 10.1099/mic.0.074286-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Five genes encoding enzymes required for l-gluconate catabolism, together with genes encoding components of putative ABC transporters, are located in a cluster in the genome of Paracoccus sp. 43P. A gene encoding a transcriptional regulator in the IclR family, lgnR, is located in front of the cluster in the opposite direction. Reverse transcription PCR analysis indicated that the cluster was transcribed as an operon, termed the lgn operon. Two promoters, P
lgnA
and P
lgnR
, are divergently located in the intergenic region, and transcription from these promoters was induced by addition of l-gluconate or d-idonate, a catabolite of l-gluconate. Deletion of lgnR resulted in constitutive expression of lgnA, lgnH and lgnR, indicating that lgnR encodes a repressor protein for the expression of the lgn operon and lgnR itself. Electrophoretic mobility shift assay and DNase I footprinting analyses revealed that recombinant LgnR binds to both P
lgnA
and P
lgnR
, indicating that LgnR represses transcription from these promoters by competing with RNA polymerase for binding to these sequences. d-Idonate was identified as a candidate effector molecule for dissociation of LgnR from these promoters. Phylogenetic analysis revealed that LgnR formed a cluster with putative proteins from other genome sequences, which is distinct from those proteins of known regulatory functions, in the IclR family of transcriptional regulators. Additionally, the phylogeny suggests an evolutionary linkage between the l-gluconate catabolic pathway and d-galactonate catabolic pathways distributed in Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria and Actinobacteria.
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