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Kita K, Yoshida S, Masuo S, Nakamura A, Ishikawa S, Yoshida KI. Genes encoding a novel thermostable bacteriocin in the thermophilic bacterium Aeribacillus pallidus PI8. J Appl Microbiol 2023; 134:lxad293. [PMID: 38040658 DOI: 10.1093/jambio/lxad293] [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: 06/13/2023] [Revised: 11/10/2023] [Accepted: 11/30/2023] [Indexed: 12/03/2023]
Abstract
AIM Aeribacillus pallidus PI8 is a Gram-positive thermophilic bacterium that produces thermostable antimicrobial substances against several bacterial species, including Geobacillus kaustophilus HTA426. In the present study, we sought to identify genes of PI8 with antibacterial activity. METHODS AND RESULTS We isolated, cloned, and characterized a thermostable bacteriocin from A. pallidus PI8 and named it pallidocyclin. Mass spectrometric analyses of pallidocyclin revealed that it had a circular peptide structure, and its precursor was encoded by pcynA in the PI8 genome. pcynA is the second gene within the pcynBACDEF operon. Expression of the full-length pcynBACDEF operon in Bacillus subtilis produced intact pallidocyclin, whereas expression of pcynF in G. kaustophilus HTA426 conferred resistance to pallidocyclin. CONCLUSION Aeribacillus pallidus PI8 possesses the pcynBACDEF operon to produce pallidocyclin. pcynA encodes the pallidocyclin precursor, and pcynF acts as an antagonist of pallidocyclin.
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Affiliation(s)
- Kyosuke Kita
- Department of Science, Technology, and Innovation, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
| | - Sanako Yoshida
- Department of Science, Technology, and Innovation, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
| | - Shunsuke Masuo
- Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8572 Ibaraki, Japan
- Microbiology Research Center for Sustainability, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8572 Ibaraki, Japan
| | - Akira Nakamura
- Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8572 Ibaraki, Japan
- Microbiology Research Center for Sustainability, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8572 Ibaraki, Japan
| | - Shu Ishikawa
- Department of Science, Technology, and Innovation, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
| | - Ken-Ichi Yoshida
- Department of Science, Technology, and Innovation, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
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Matsuoka S, Shimizu Y, Nobe K, Matsumoto K, Asai K, Hara H. Glucolipids and lipoteichoic acids affect the activity of SigI, an alternative sigma factor, and WalKR, an essential two-component system, in Bacillus subtilis. Genes Cells 2021; 27:77-92. [PMID: 34910349 DOI: 10.1111/gtc.12912] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Revised: 12/09/2021] [Accepted: 12/10/2021] [Indexed: 11/29/2022]
Abstract
In a Bacillus subtilis ugtP mutant lacking glucolipids, SigI was activated in the log phase, and the activation of SigI in the mutant was suppressed by the expression of native ugtP. By contrast, SigI was inhibited in a yfnI mutant lacking one of the lipoteichoic acid (LTA) synthase genes, and the inhibition was suppressed by the expression of yfnI. A series of mutation analyses of the sigI promoter revealed that the two WalR binding sites were involved in the increase of PsigI -lacZ activity in the ugtP mutant and decrease of the lacZ activity in the yfnI mutant. Transcription from the SigI recognition sequence was enhanced in the ugtP mutant, whereas yfnI disruption inhibited the transcription from the SigA recognition sequence in the sigI promoter. We found that not only SigI but also WalKR, the essential two-component system, was activated in the ugtP mutant and inhibited in the yfnI mutant. The walK mutants with activated WalR exhibited abnormal morphology, but this phenotype was suppressed by the addition of MgSO4 . We conclude that glucolipids and LTA are key compounds in the maintenance of normal cell surface structure in B. subtilis.
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Affiliation(s)
- Satoshi Matsuoka
- Department of Biochemistry and Molecular Biology, Graduate School of Science and Engineering, Saitama University, Saitama, Japan
| | - Yoko Shimizu
- Department of Biochemistry and Molecular Biology, Graduate School of Science and Engineering, Saitama University, Saitama, Japan
| | - Kaori Nobe
- Department of Biochemistry and Molecular Biology, Graduate School of Science and Engineering, Saitama University, Saitama, Japan
| | - Kouji Matsumoto
- Department of Biochemistry and Molecular Biology, Graduate School of Science and Engineering, Saitama University, Saitama, Japan
| | - Kei Asai
- Department of Biochemistry and Molecular Biology, Graduate School of Science and Engineering, Saitama University, Saitama, Japan.,Department of Bioscience, Faculty of Life Science, Tokyo University of Agriculture, Tokyo, Japan
| | - Hiroshi Hara
- Department of Biochemistry and Molecular Biology, Graduate School of Science and Engineering, Saitama University, Saitama, Japan
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3
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Gotoh Y, Kita K, Tanaka K, Ishikawa S, Suzuki T, Yoshida KI. Genome sequences of two strains of Lactococcus lactis subsp. cremoris with the same ancestry but a different capacity to produce exopolysaccharides. J GEN APPL MICROBIOL 2021; 67:220-223. [PMID: 34334502 DOI: 10.2323/jgam.2021.03.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Strains of Lactococcus lactis subsp. cremoris are used to produce yogurt containing exopolysaccharides with a sticky texture. When strain G3-2 producing exopolysaccharides was grown at elevated temperatures, a spontaneous mutant EPSC, which had lost exopolysaccharides biosynthesis, was isolated. Genomes of the two strains were determined to be composed of a 2.4-Mb chromosome and up to eleven plasmids, and it was revealed that one of the plasmids encoding the gene cluster for exopolysaccharides biosynthesis was lost selectively in EPSC.
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Affiliation(s)
| | - Kyosuke Kita
- Department of Science, Technology and Innovation, Kobe University
| | - Kosei Tanaka
- Department of Science, Technology and Innovation, Kobe University
| | - Shu Ishikawa
- Department of Science, Technology and Innovation, Kobe University
| | | | - Ken-Ichi Yoshida
- Department of Science, Technology and Innovation, Kobe University
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Complete Genome Sequence of Nitrogen-Fixing Paenibacillus sp. Strain URB8-2, Isolated from the Rhizosphere of Wild Grass. Microbiol Resour Announc 2020; 9:9/36/e00814-20. [PMID: 32883790 PMCID: PMC7471385 DOI: 10.1128/mra.00814-20] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Abstract
We report here the complete genome sequence of nitrogen-fixing Paenibacillus sp. strain URB8-2, isolated from the rhizosphere of wild grass in Kobe, Japan, revealing that this bacterium is related to Paenibacillus rhizophilus 7197, a novel species collected recently in Inner Mongolia, China, and that it possesses two gene clusters for distinct types of nitrogenases. We report here the complete genome sequence of nitrogen-fixing Paenibacillus sp. strain URB8-2, isolated from the rhizosphere of wild grass in Kobe, Japan, revealing that this bacterium is related to Paenibacillus rhizophilus 7197, a novel species collected recently in Inner Mongolia, China, and that it possesses two gene clusters for distinct types of nitrogenases.
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5
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Complete Genome Sequence of Thermophilic Bacterium Aeribacillus pallidus PI8. Microbiol Resour Announc 2020; 9:9/17/e00224-20. [PMID: 32327509 PMCID: PMC7180282 DOI: 10.1128/mra.00224-20] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Here, we report the complete genome sequence of Aeribacillus pallidus PI8, a thermophilic bacterium, isolated from soybean stem extract. The sequence was determined using Illumina and Nanopore sequencers. Bioinformatic analyses of the genome sequence revealed the presence of possible bacteriocin gene clusters. Here, we report the complete genome sequence of Aeribacillus pallidus PI8, a thermophilic bacterium, isolated from soybean stem extract. The sequence was determined using Illumina and Nanopore sequencers. Bioinformatic analyses of the genome sequence revealed the presence of possible bacteriocin gene clusters.
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Michon C, Kang CM, Karpenko S, Tanaka K, Ishikawa S, Yoshida KI. A bacterial cell factory converting glucose into scyllo-inositol, a therapeutic agent for Alzheimer's disease. Commun Biol 2020; 3:93. [PMID: 32123276 PMCID: PMC7052218 DOI: 10.1038/s42003-020-0814-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2019] [Accepted: 02/11/2020] [Indexed: 12/28/2022] Open
Abstract
A rare stereoisomer of inositol, scyllo-inositol, is a therapeutic agent that has shown potential efficacy in preventing Alzheimer’s disease. Mycobacterium tuberculosis ino1 encoding myo-inositol-1-phosphate (MI1P) synthase (MI1PS) was introduced into Bacillus subtilis to convert glucose-6-phosphate (G6P) into MI1P. We found that inactivation of pbuE elevated intracellular concentrations of NAD+·NADH as an essential cofactor of MI1PS and was required to activate MI1PS. MI1P thus produced was dephosphorylated into myo-inositol by an intrinsic inositol monophosphatase, YktC, which was subsequently isomerized into scyllo-inositol via a previously established artificial pathway involving two inositol dehydrogenases, IolG and IolW. In addition, both glcP and glcK were overexpressed to feed more G6P and accelerate scyllo-inositol production. Consequently, a B. subtilis cell factory was demonstrated to produce 2 g L−1scyllo-inositol from 20 g L−1 glucose. This cell factory provides an inexpensive way to produce scyllo-inositol, which will help us to challenge the growing problem of Alzheimer’s disease in our aging society. Michon et al. describe the use of a recombinant Bacillus subtilis as a cell factory capable of producing scyllo-inositol, a therapeutic compound for Alzheimer’s disease, from inexpensive glucose. They demonstrate that it could produce 2 g L−1 of scyllo-inositol from 20 g L−1 glucose.
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Affiliation(s)
- Christophe Michon
- Department of Science, Technology and Innovation, Kobe University, Kobe, 657 8501, Japan.,CHROMagar, 4 Place du 18 Juin 1940, 75006, Paris, France
| | - Choong-Min Kang
- Department of Biological Sciences, California State University, Stanislaus, Turlock, CA, 95382, USA
| | - Sophia Karpenko
- Department of Science, Technology and Innovation, Kobe University, Kobe, 657 8501, Japan.,Sorbonne Universités, UPMC Univ. Paris 06, UMR 8237, Laboratoire Jean Perrin, F-75005, Paris, France.,CNRS UMR 8237, Laboratoire Jean Perrin, F-75005, Paris, France.,Paris Sciences & Lettres, 60 rue Mazarine, F-75006, Paris, France
| | - Kosei Tanaka
- Department of Science, Technology and Innovation, Kobe University, Kobe, 657 8501, Japan
| | - Shu Ishikawa
- Department of Science, Technology and Innovation, Kobe University, Kobe, 657 8501, Japan
| | - Ken-Ichi Yoshida
- Department of Science, Technology and Innovation, Kobe University, Kobe, 657 8501, Japan.
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7
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Yan P, Wu Y, Yang L, Wang Z, Chen T. Engineering genome-reduced Bacillus subtilis for acetoin production from xylose. Biotechnol Lett 2017; 40:393-398. [PMID: 29236191 DOI: 10.1007/s10529-017-2481-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2017] [Accepted: 11/13/2017] [Indexed: 11/24/2022]
Abstract
OBJECTIVES To investigate the capacity of a genome-reduced Bacillus subtilis strain as chassis cell for acetoin production from xylose. RESULTS To endow the genome-reduced Bacillus subtilis strain BSK814 with the ability to utilize xylose, we inserted a native xyl operon into its genome and deleted the araR gene. The resulting strain BSK814A2 produced 2.94 g acetoin/l from 10 g xylose/l, which was 39% higher than control strain BSK19A2. The deletion of the bdhA and acoA genes further improved xylose utilization efficiency and increased acetoin production to 3.71 g/l in BSK814A4. Finally, BSK814A4 produced up to 23.3 g acetoin/l from 50 g xylose/l, with a yield of 0.46 g/g xylose. Both the titer and yield were 39% higher than those of control strain BSK19A4. CONCLUSIONS As a chassis cell, genome-reduced B. subtilis showed significantly improved capacity for the production of the overflow product acetoin from xylose compared with wild-type strain.
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Affiliation(s)
- Panpan Yan
- Key Laboratory of Systems Bioengineering (Ministry of Education), SynBio Research Platform, Collaborative Innovation Center for Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China
| | - Yuanqing Wu
- Key Laboratory of Systems Bioengineering (Ministry of Education), SynBio Research Platform, Collaborative Innovation Center for Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China
| | - Li Yang
- Key Laboratory of Systems Bioengineering (Ministry of Education), SynBio Research Platform, Collaborative Innovation Center for Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China.,College of life Science, Shihezi University, Shihezi, 832000, People's Republic of China
| | - Zhiwen Wang
- Key Laboratory of Systems Bioengineering (Ministry of Education), SynBio Research Platform, Collaborative Innovation Center for Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China
| | - Tao Chen
- Key Laboratory of Systems Bioengineering (Ministry of Education), SynBio Research Platform, Collaborative Innovation Center for Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China.
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Kang DM, Michon C, Morinaga T, Tanaka K, Takenaka S, Ishikawa S, Yoshida KI. Bacillus subtilis IolQ (DegA) is a transcriptional repressor of iolX encoding NAD +-dependent scyllo-inositol dehydrogenase. BMC Microbiol 2017; 17:154. [PMID: 28693424 PMCID: PMC5504672 DOI: 10.1186/s12866-017-1065-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Accepted: 07/01/2017] [Indexed: 11/23/2022] Open
Abstract
Background Bacillus subtilis is able to utilize at least three inositol stereoisomers as carbon sources, myo-, scyllo-, and D-chiro-inositol (MI, SI, and DCI, respectively). NAD+-dependent SI dehydrogenase responsible for SI catabolism is encoded by iolX. Even in the absence of functional iolX, the presence of SI or MI in the growth medium was found to induce the transcription of iolX through an unknown mechanism. Results Immediately upstream of iolX, there is an operon that encodes two genes, yisR and iolQ (formerly known as degA), each of which could encode a transcriptional regulator. Here we performed an inactivation analysis of yisR and iolQ and found that iolQ encodes a repressor of the iolX transcription. The coding sequence of iolQ was expressed in Escherichia coli and the gene product was purified as a His-tagged fusion protein, which bound to two sites within the iolX promoter region in vitro. Conclusions IolQ is a transcriptional repressor of iolX. Genetic evidences allowed us to speculate that SI and MI might possibly be the intracellular inducers, however they failed to antagonize DNA binding of IolQ in in vitro experiments.
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Affiliation(s)
- Dong-Min Kang
- Department of Agrobioscience, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501, Japan.,Present address: Department of Plant Medicine and RILS, Gyeongsang National University, Jinju, 52828, Republic of Korea
| | - Christophe Michon
- Department of Science, Technology and Innovation, Graduate School of Science, Technology and Innovation, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501, Japan
| | - Tetsuro Morinaga
- Gene testing Business Department, LS Business Division, Sysmex Corporation, 4-4-4 Takatsukadai, Nishi, Kobe, 651-2271, Japan
| | - Kosei Tanaka
- Organization of Advanced Science and Technology, Kobe University, 1-1 Rokkodai, Nada, Kobe657, Kobe, -8501, Japan
| | - Shinji Takenaka
- Department of Agrobioscience, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501, Japan.,Organization of Advanced Science and Technology, Kobe University, 1-1 Rokkodai, Nada, Kobe657, Kobe, -8501, Japan
| | - Shu Ishikawa
- Department of Science, Technology and Innovation, Graduate School of Science, Technology and Innovation, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501, Japan
| | - Ken-Ichi Yoshida
- Organization of Advanced Science and Technology, Kobe University, 1-1 Rokkodai, Nada, Kobe657, Kobe, -8501, Japan. .,Department of Science, Technology and Innovation, Graduate School of Science, Technology and Innovation, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501, Japan.
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9
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Toya Y, Hirasawa T, Ishikawa S, Chumsakul O, Morimoto T, Liu S, Masuda K, Kageyama Y, Ozaki K, Ogasawara N, Shimizu H. Enhanced dipicolinic acid production during the stationary phase in Bacillus subtilis by blocking acetoin synthesis. Biosci Biotechnol Biochem 2015; 79:2073-80. [DOI: 10.1080/09168451.2015.1060843] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Abstract
Bacterial bio-production during the stationary phase is expected to lead to a high target yield because the cells do not consume the substrate for growth. Bacillus subtilis is widely used for bio-production, but little is known about the metabolism during the stationary phase. In this study, we focused on the dipicolinic acid (DPA) production by B. subtilis and investigated the metabolism. We found that DPA production competes with acetoin synthesis and that acetoin synthesis genes (alsSD) deletion increases DPA productivity by 1.4-fold. The mutant showed interesting features where the glucose uptake was inhibited, whereas the cell density increased by approximately 50%, resulting in similar volumetric glucose consumption to that of the parental strain. The metabolic profiles revealed accumulation of pyruvate, acetyl-CoA, and the TCA cycle intermediates in the alsSD mutant. Our results indicate that alsSD-deleted B. subtilis has potential as an effective host for stationary-phase production of compounds synthesized from these intermediates.
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Affiliation(s)
- Yoshihiro Toya
- Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, Osaka University, Suita, Japan
- Advanced Low Carbon Technology Research and Development Program, Japan Science and Technology Agency (JST, ALCA), Japan
| | - Takashi Hirasawa
- Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, Osaka University, Suita, Japan
- Advanced Low Carbon Technology Research and Development Program, Japan Science and Technology Agency (JST, ALCA), Japan
- Department of Bioengineering, Tokyo Institute of Technology, Yokohama, Japan
| | - Shu Ishikawa
- Advanced Low Carbon Technology Research and Development Program, Japan Science and Technology Agency (JST, ALCA), Japan
- Graduate School of Biological Science, Nara Institute of Science and Technology, Ikoma, Japan
| | - Onuma Chumsakul
- Advanced Low Carbon Technology Research and Development Program, Japan Science and Technology Agency (JST, ALCA), Japan
- Graduate School of Biological Science, Nara Institute of Science and Technology, Ikoma, Japan
| | - Takuya Morimoto
- Advanced Low Carbon Technology Research and Development Program, Japan Science and Technology Agency (JST, ALCA), Japan
- Biological Science Laboratories, Kao Corporation, Haga, Japan
| | - Shenghao Liu
- Advanced Low Carbon Technology Research and Development Program, Japan Science and Technology Agency (JST, ALCA), Japan
- Biological Science Laboratories, Kao Corporation, Haga, Japan
| | - Kenta Masuda
- Advanced Low Carbon Technology Research and Development Program, Japan Science and Technology Agency (JST, ALCA), Japan
- Biological Science Laboratories, Kao Corporation, Haga, Japan
| | - Yasushi Kageyama
- Advanced Low Carbon Technology Research and Development Program, Japan Science and Technology Agency (JST, ALCA), Japan
- Biological Science Laboratories, Kao Corporation, Haga, Japan
| | - Katsuya Ozaki
- Advanced Low Carbon Technology Research and Development Program, Japan Science and Technology Agency (JST, ALCA), Japan
- Biological Science Laboratories, Kao Corporation, Haga, Japan
| | - Naotake Ogasawara
- Advanced Low Carbon Technology Research and Development Program, Japan Science and Technology Agency (JST, ALCA), Japan
- Graduate School of Biological Science, Nara Institute of Science and Technology, Ikoma, Japan
| | - Hiroshi Shimizu
- Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, Osaka University, Suita, Japan
- Advanced Low Carbon Technology Research and Development Program, Japan Science and Technology Agency (JST, ALCA), Japan
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The ResD response regulator, through functional interaction with NsrR and fur, plays three distinct roles in Bacillus subtilis transcriptional control. J Bacteriol 2013; 196:493-503. [PMID: 24214949 DOI: 10.1128/jb.01166-13] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The ResD response regulator activates transcription of diverse genes in Bacillus subtilis in response to oxygen limitation. ResD regulon genes that are the most highly induced during nitrate respiration include the nitrite reductase operon (nasDEF) and the flavohemoglobin gene (hmp), whose products function in nitric oxide (NO) metabolism. Transcription of these genes is also under the negative control of the NO-sensitive NsrR repressor. Recent studies showed that the NsrR regulon contains genes with no apparent relevance to NO metabolism and that the ResD response regulator and NsrR coordinately regulate transcription. To determine whether these genes are direct targets of NsrR and ResD, we used chromatin affinity precipitation coupled with tiling chip (ChAP-chip) and ChAP followed by quantitative PCR (ChAP-qPCR) analyses. The study showed that ResD and NsrR directly control transcription of the ykuNOP operon in the Fur regulon. ResD functions as an activator at the nasD and hmp promoters, whereas it functions at the ykuN promoter as an antirepressor of Fur and a corepressor for NsrR. This mechanism likely participates in fine-tuning of transcript levels in response to different sources of stress, such as oxygen limitation, iron limitation, and exposure to NO.
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