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Gu Q, Zhu X, Ma J, Jiang T, Pan Z, Yao H. Functional analysis of the type II toxin-antitoxin system ParDE in Streptococcus suis serotype 2. BMC Vet Res 2025; 21:30. [PMID: 39833840 PMCID: PMC11744833 DOI: 10.1186/s12917-024-04069-w] [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: 01/25/2024] [Accepted: 05/08/2024] [Indexed: 01/22/2025] Open
Abstract
Streptococcus suis (S. suis) is a major pathogen in swine and poses a potential zoonotic threat, which may cause serious diseases. Many toxin-antitoxin (TA) systems have been discovered in S. suis, but their functions have not yet been fully elucidated. In this study, an auto-regulating type II TA system, ParDE, was identified in S. suis serotype 2 strain ZY05719. We constructed a mutant strain, ΔparDE, to explore its functions in bacterial virulence, various stress responses, and biofilm formation capabilities. The toxicity exerted by the toxin ParE can be neutralized by the antitoxin ParD. The β-galactosidase activity analysis indicated that ParDE has an autoregulatory function. An electrophoretic mobility shift assay (EMSA) confirmed that the antitoxin ParD bound to the promoter of ParDE as dimers. In the mouse infection model, the deletion of ParDE in ZY05719 significantly attenuated virulence. ΔparDE also exhibited a reduced anti-oxidative stress ability, and ΔparDE was more susceptible to phagocytosis and killing by macrophages. Moreover, the biofilm formation ability of the ΔparDE strain was significantly enhanced compared to ZY05719. Taken together, these findings indicate that the type II TA system ParDE plays a significant role in the pathogenesis of S. suis, providing new insights into its pathogenic mechanisms.
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Affiliation(s)
- Qibing Gu
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China
- Key Lab of Animal Bacteriology, Ministry of Agriculture, Nanjing, 210095, China
- OIE Reference Lab for Swine Streptococcosis, Nanjing, 210095, China
| | - Xiayu Zhu
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China
- Key Lab of Animal Bacteriology, Ministry of Agriculture, Nanjing, 210095, China
- OIE Reference Lab for Swine Streptococcosis, Nanjing, 210095, China
| | - Jiale Ma
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China
- Key Lab of Animal Bacteriology, Ministry of Agriculture, Nanjing, 210095, China
- OIE Reference Lab for Swine Streptococcosis, Nanjing, 210095, China
| | - Tao Jiang
- Department of Stomatology, Jinling Hospital, Affiliated Hospital of Medical School, Nanjing University, Nanjing, China.
| | - Zihao Pan
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.
- Key Lab of Animal Bacteriology, Ministry of Agriculture, Nanjing, 210095, China.
- OIE Reference Lab for Swine Streptococcosis, Nanjing, 210095, China.
| | - Huochun Yao
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China
- Key Lab of Animal Bacteriology, Ministry of Agriculture, Nanjing, 210095, China
- OIE Reference Lab for Swine Streptococcosis, Nanjing, 210095, China
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2
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Bustamante P, Ramos-Corominas MN, Martinez-Medina M. Contribution of Toxin-Antitoxin Systems to Adherent-Invasive E. coli Pathogenesis. Microorganisms 2024; 12:1158. [PMID: 38930540 PMCID: PMC11205521 DOI: 10.3390/microorganisms12061158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2024] [Revised: 05/24/2024] [Accepted: 06/05/2024] [Indexed: 06/28/2024] Open
Abstract
Pathobionts have been implicated in various chronic diseases, including Crohn's disease (CD), a multifactorial chronic inflammatory condition that primarily affects the gastrointestinal tract, causing inflammation and damage to the digestive system. While the exact cause of CD remains unclear, adherent-invasive Escherichia coli (AIEC) strains have emerged as key contributors to its pathogenesis. AIEC are characterized by their ability to adhere to and invade intestinal epithelial cells and survive and replicate inside macrophages. However, the mechanisms underlying the virulence and persistence of AIEC within their host remain the subject of intensive research. Toxin-antitoxin systems (TAs) play a potential role in AIEC pathogenesis and may be therapeutic targets. These systems generally consist of two components: a toxin harmful to the cell and an antitoxin that neutralizes the toxin's effects. They contribute to bacterial survival in adverse conditions and regulate bacterial growth and behavior, affecting various cellular processes in bacterial pathogens. This review focuses on the current information available to determine the roles of TAs in the pathogenicity of AIEC. Their contribution to the AIEC stress response, biofilm formation, phage inhibition, the maintenance of mobile genetic elements, and host lifestyles is discussed.
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Affiliation(s)
- Paula Bustamante
- Molecular and Cellular Microbiology Laboratory, Instituto de Ciencias Biomédicas, Facultad de Ciencias de la Salud, Universidad Autónoma de Chile, Santiago 8910060, Chile
| | - María Núria Ramos-Corominas
- Microbiology of Intestinal Diseases, Biology Department, Universitat de Girona, 17003 Girona, Spain; (M.N.R.-C.); (M.M.-M.)
| | - Margarita Martinez-Medina
- Microbiology of Intestinal Diseases, Biology Department, Universitat de Girona, 17003 Girona, Spain; (M.N.R.-C.); (M.M.-M.)
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3
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Gu Q, Zhu X, Yu Y, Jiang T, Pan Z, Ma J, Yao H. Type II and IV toxin-antitoxin systems coordinately stabilize the integrative and conjugative element of the ICESa2603 family conferring multiple drug resistance in Streptococcus suis. PLoS Pathog 2024; 20:e1012169. [PMID: 38640137 PMCID: PMC11062541 DOI: 10.1371/journal.ppat.1012169] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2024] [Revised: 05/01/2024] [Accepted: 04/02/2024] [Indexed: 04/21/2024] Open
Abstract
Integrative and conjugative elements (ICEs) play a vital role in bacterial evolution by carrying essential genes that confer adaptive functions to the host. Despite their importance, the mechanism underlying the stable inheritance of ICEs, which is necessary for the acquisition of new traits in bacteria, remains poorly understood. Here, we identified SezAT, a type II toxin-antitoxin (TA) system, and AbiE, a type IV TA system encoded within the ICESsuHN105, coordinately promote ICE stabilization and mediate multidrug resistance in Streptococcus suis. Deletion of SezAT or AbiE did not affect the strain's antibiotic susceptibility, but their duple deletion increased susceptibility, mainly mediated by the antitoxins SezA and AbiEi. Further studies have revealed that SezA and AbiEi affect the genetic stability of ICESsuHN105 by moderating the excision and extrachromosomal copy number, consequently affecting the antibiotic resistance conferred by ICE. The DNA-binding proteins AbiEi and SezA, which bind palindromic sequences in the promoter, coordinately modulate ICE excision and extracellular copy number by binding to sequences in the origin-of-transfer (oriT) and the attL sites, respectively. Furthermore, AbiEi negatively regulates the transcription of SezAT by binding directly to its promoter, optimizing the coordinate network of SezAT and AbiE in maintaining ICESsuHN105 stability. Importantly, SezAT and AbiE are widespread and conserved in ICEs harbouring diverse drug-resistance genes, and their coordinated effects in promoting ICE stability and mediating drug resistance may be broadly applicable to other ICEs. Altogether, our study uncovers the TA system's role in maintaining the genetic stability of ICE and offers potential targets for overcoming the dissemination and evolution of drug resistance.
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Affiliation(s)
- Qibing Gu
- MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China
- Key Lab of Animal Bacteriology, Ministry of Agriculture, Nanjing, China
- OIE Reference Lab for Swine Streptococcosis, Nanjing, China
| | - Xiayu Zhu
- MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China
- Key Lab of Animal Bacteriology, Ministry of Agriculture, Nanjing, China
- OIE Reference Lab for Swine Streptococcosis, Nanjing, China
| | - Yong Yu
- MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China
- Key Lab of Animal Bacteriology, Ministry of Agriculture, Nanjing, China
- OIE Reference Lab for Swine Streptococcosis, Nanjing, China
| | - Tao Jiang
- Department of Stomatology, Jinling Hospital, Affiliated Hospital of Medical School, Nanjing University, Nanjing, China
| | - Zihao Pan
- MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China
- Key Lab of Animal Bacteriology, Ministry of Agriculture, Nanjing, China
- OIE Reference Lab for Swine Streptococcosis, Nanjing, China
| | - Jiale Ma
- MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China
- Key Lab of Animal Bacteriology, Ministry of Agriculture, Nanjing, China
- OIE Reference Lab for Swine Streptococcosis, Nanjing, China
| | - Huochun Yao
- MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China
- Key Lab of Animal Bacteriology, Ministry of Agriculture, Nanjing, China
- OIE Reference Lab for Swine Streptococcosis, Nanjing, China
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Guan J, Chen Y, Goh YX, Wang M, Tai C, Deng Z, Song J, Ou HY. TADB 3.0: an updated database of bacterial toxin-antitoxin loci and associated mobile genetic elements. Nucleic Acids Res 2024; 52:D784-D790. [PMID: 37897352 PMCID: PMC10767807 DOI: 10.1093/nar/gkad962] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Revised: 10/11/2023] [Accepted: 10/14/2023] [Indexed: 10/30/2023] Open
Abstract
TADB 3.0 (https://bioinfo-mml.sjtu.edu.cn/TADB3/) is an updated database that provides comprehensive information on bacterial types I to VIII toxin-antitoxin (TA) loci. Compared with the previous version, three major improvements are introduced: First, with the aid of text mining and manual curation, it records the details of 536 TA loci with experimental support, including 102, 403, 8, 14, 1, 1, 3 and 4 TA loci of types I to VIII, respectively; Second, by leveraging the upgraded TA prediction tool TAfinder 2.0 with a stringent strategy, TADB 3.0 collects 211 697 putative types I to VIII TA loci predicted in 34 789 completely sequenced prokaryotic genomes, providing researchers with a large-scale dataset for further follow-up analysis and characterization; Third, based on their genomic locations, relationships of 69 019 TA loci and 60 898 mobile genetic elements (MGEs) are visualized by interactive networks accessible through the user-friendly web page. With the recent updates, TADB 3.0 may provide improved in silico support for comprehending the biological roles of TA pairs in prokaryotes and their functional associations with MGEs.
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Affiliation(s)
- Jiahao Guan
- State Key Laboratory of Microbial Metabolism, Joint International Laboratory on Metabolic & Developmental Sciences, School of Life Sciences & Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Yongkui Chen
- State Key Laboratory of Microbial Metabolism, Joint International Laboratory on Metabolic & Developmental Sciences, School of Life Sciences & Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Ying-Xian Goh
- State Key Laboratory of Microbial Metabolism, Joint International Laboratory on Metabolic & Developmental Sciences, School of Life Sciences & Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Meng Wang
- State Key Laboratory of Microbial Metabolism, Joint International Laboratory on Metabolic & Developmental Sciences, School of Life Sciences & Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Cui Tai
- State Key Laboratory of Microbial Metabolism, Joint International Laboratory on Metabolic & Developmental Sciences, School of Life Sciences & Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Zixin Deng
- State Key Laboratory of Microbial Metabolism, Joint International Laboratory on Metabolic & Developmental Sciences, School of Life Sciences & Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Jiangning Song
- Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Melbourne, VIC 3800, Australia
- Monash Data Futures Institute, Monash University, Melbourne, VIC 3800, Australia
| | - Hong-Yu Ou
- State Key Laboratory of Microbial Metabolism, Joint International Laboratory on Metabolic & Developmental Sciences, School of Life Sciences & Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China
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5
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Pizzolato-Cezar LR, Spira B, Machini MT. Bacterial toxin-antitoxin systems: Novel insights on toxin activation across populations and experimental shortcomings. CURRENT RESEARCH IN MICROBIAL SCIENCES 2023; 5:100204. [PMID: 38024808 PMCID: PMC10643148 DOI: 10.1016/j.crmicr.2023.100204] [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] [Indexed: 12/01/2023] Open
Abstract
The alarming rise in hard-to-treat bacterial infections is of great concern to human health. Thus, the identification of molecular mechanisms that enable the survival and growth of pathogens is of utmost urgency for the development of more efficient antimicrobial therapies. In challenging environments, such as presence of antibiotics, or during host infection, metabolic adjustments are essential for microorganism survival and competitiveness. Toxin-antitoxin systems (TASs) consisting of a toxin with metabolic modulating activity and a cognate antitoxin that antagonizes that toxin are important elements in the arsenal of bacterial stress defense. However, the exact physiological function of TA systems is highly debatable and with the exception of stabilization of mobile genetic elements and phage inhibition, other proposed biological functions lack a broad consensus. This review aims at gaining new insights into the physiological effects of TASs in bacteria and exploring the experimental shortcomings that lead to discrepant results in TAS research. Distinct control mechanisms ensure that only subsets of cells within isogenic cultures transiently develop moderate levels of toxin activity. As a result, TASs cause phenotypic growth heterogeneity rather than cell stasis in the entire population. It is this feature that allows bacteria to thrive in diverse environments through the creation of subpopulations with different metabolic rates and stress tolerance programs.
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Affiliation(s)
- Luis R. Pizzolato-Cezar
- Department of Biochemistry, Institute of Chemistry, University of São Paulo, São Paulo, Brazil
| | - Beny Spira
- Department of Microbiology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil
| | - M. Teresa Machini
- Department of Biochemistry, Institute of Chemistry, University of São Paulo, São Paulo, Brazil
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6
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Boss L, Kędzierska B. Bacterial Toxin-Antitoxin Systems' Cross-Interactions-Implications for Practical Use in Medicine and Biotechnology. Toxins (Basel) 2023; 15:380. [PMID: 37368681 DOI: 10.3390/toxins15060380] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2023] [Revised: 05/30/2023] [Accepted: 06/02/2023] [Indexed: 06/29/2023] Open
Abstract
Toxin-antitoxin (TA) systems are widely present in bacterial genomes. They consist of stable toxins and unstable antitoxins that are classified into distinct groups based on their structure and biological activity. TA systems are mostly related to mobile genetic elements and can be easily acquired through horizontal gene transfer. The ubiquity of different homologous and non-homologous TA systems within a single bacterial genome raises questions about their potential cross-interactions. Unspecific cross-talk between toxins and antitoxins of non-cognate modules may unbalance the ratio of the interacting partners and cause an increase in the free toxin level, which can be deleterious to the cell. Moreover, TA systems can be involved in broadly understood molecular networks as transcriptional regulators of other genes' expression or modulators of cellular mRNA stability. In nature, multiple copies of highly similar or identical TA systems are rather infrequent and probably represent a transition stage during evolution to complete insulation or decay of one of them. Nevertheless, several types of cross-interactions have been described in the literature to date. This implies a question of the possibility and consequences of the TA system cross-interactions, especially in the context of the practical application of the TA-based biotechnological and medical strategies, in which such TAs will be used outside their natural context, will be artificially introduced and induced in the new hosts. Thus, in this review, we discuss the prospective challenges of system cross-talks in the safety and effectiveness of TA system usage.
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Affiliation(s)
- Lidia Boss
- Department of Bacterial Molecular Genetics, Faculty of Biology, University of Gdańsk, 80-309 Gdańsk, Poland
| | - Barbara Kędzierska
- Department of Bacterial Molecular Genetics, Faculty of Biology, University of Gdańsk, 80-309 Gdańsk, Poland
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7
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Deletion of lacD gene affected stress tolerance and virulence of Streptococcus suis serotype 2. J Microbiol 2022; 60:948-959. [DOI: 10.1007/s12275-022-2146-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2022] [Revised: 05/27/2022] [Accepted: 06/24/2022] [Indexed: 11/25/2022]
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8
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Qiu J, Zhai Y, Wei M, Zheng C, Jiao X. Toxin–antitoxin systems: Classification, biological roles, and applications. Microbiol Res 2022; 264:127159. [DOI: 10.1016/j.micres.2022.127159] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2022] [Revised: 08/02/2022] [Accepted: 08/03/2022] [Indexed: 11/28/2022]
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9
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Choi E, Huh A, Oh C, Oh JI, Kang HY, Hwang J. Functional characterization of HigBA toxin-antitoxin system in an Arctic bacterium, Bosea sp. PAMC 26642. J Microbiol 2022; 60:192-206. [PMID: 35102526 DOI: 10.1007/s12275-022-1619-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Revised: 12/15/2021] [Accepted: 12/20/2021] [Indexed: 01/02/2023]
Abstract
Toxin-antitoxin (TA) systems are growth-controlling genetic elements consisting of an intracellular toxin protein and its cognate antitoxin. TA systems have been spread among microbial genomes through horizontal gene transfer and are now prevalent in most bacterial and archaeal genomes. Under normal growth conditions, antitoxins tightly counteract the activity of the toxins. Upon stresses, antitoxins are inactivated, releasing activated toxins, which induce growth arrest or cell death. In this study, among nine functional TA modules in Bosea sp. PAMC 26642 living in Arctic lichen, we investigated the functionality of BoHigBA2. BohigBA2 is located close to a genomic island and adjacent to flagellar gene clusters. The expression of BohigB2 induced the inhibition of E. coli growth at 37°C, which was more manifest at 18°C, and this growth defect was reversed when BohigA2 was co-expressed, suggesting that this BoHigBA2 module might be an active TA module in Bosea sp. PAMC 26642. Live/dead staining and viable count analyses revealed that the BoHigB2 toxin had a bactericidal effect, causing cell death. Furthermore, we demonstrated that BoHigB2 possessed mRNA-specific ribonuclease activity on various mRNAs and cleaved only mRNAs being translated, which might impede overall translation and consequently lead to cell death. Our study provides the insight to understand the cold adaptation of Bosea sp. PAMC 26642 living in the Arctic.
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Affiliation(s)
- Eunsil Choi
- Department of Microbiology, Pusan National University, Busan, 46241, Republic of Korea.,Microbiological Resource Research Institute, Pusan National University, Busan, 46241, Republic of Korea
| | - Ahhyun Huh
- Department of Microbiology, Pusan National University, Busan, 46241, Republic of Korea
| | - Changmin Oh
- Department of Microbiology, Pusan National University, Busan, 46241, Republic of Korea
| | - Jeong-Il Oh
- Department of Microbiology, Pusan National University, Busan, 46241, Republic of Korea.,Microbiological Resource Research Institute, Pusan National University, Busan, 46241, Republic of Korea
| | - Ho Young Kang
- Department of Microbiology, Pusan National University, Busan, 46241, Republic of Korea.,Microbiological Resource Research Institute, Pusan National University, Busan, 46241, Republic of Korea
| | - Jihwan Hwang
- Department of Microbiology, Pusan National University, Busan, 46241, Republic of Korea. .,Microbiological Resource Research Institute, Pusan National University, Busan, 46241, Republic of Korea.
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10
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Genome analysis provides insight into hyper-virulence of Streptococcus suis LSM178, a human strain with a novel sequence type 1005. Sci Rep 2021; 11:23919. [PMID: 34907269 PMCID: PMC8671398 DOI: 10.1038/s41598-021-03370-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Accepted: 11/30/2021] [Indexed: 11/16/2022] Open
Abstract
Streptococcus suis has been well-recognized as a zoonotic pathogen worldwide, and the diversity and unpredictable adaptive potential of sporadic human strains represent a great risk to the public health. In this study, S. suis LSM178, isolated from a patient in contact with pigs and raw pork, was assessed as a hyper-virulent strain and interpreted for the virulence based on its genetic information. The strain was more invasive for Caco-2 cells than two other S. suis strains, SC19 and P1/7. Sequence analysis designated LSM178 with serotype 2 and a novel sequence type 1005. Phylogenetic analysis showed that LSM178 clustered with highly virulent strains including all human strains and epidemic strains. Compared with other strains, these S. suis have the most and the same virulent factors and a type I-89 K pathogenicity island. Further, groups of genes were identified to distinguish these highly virulent strains from other generally virulent strains, emphasizing the key roles of genes modeling transcription, cell barrier, replication, recombination and repair on virulence regulation. Additionally, LSM178 contains a novel prophage conducive potentially to pathogenicity.
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11
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Gu Q, He P, Wang D, Ma J, Zhong X, Zhu Y, Zhang Y, Bai Q, Pan Z, Yao H. An Auto-Regulating Type II Toxin-Antitoxin System Modulates Drug Resistance and Virulence in Streptococcus suis. Front Microbiol 2021; 12:671706. [PMID: 34475853 PMCID: PMC8406773 DOI: 10.3389/fmicb.2021.671706] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Accepted: 05/26/2021] [Indexed: 11/13/2022] Open
Abstract
Toxin-antitoxin (TA) systems are ubiquitous genetic elements that play an essential role in multidrug tolerance and virulence of bacteria. So far, little is known about the TA systems in Streptococcus suis. In this study, the Xress-MNTss TA system, composed of the MNTss toxin in the periplasmic space and its interacting Xress antitoxin, was identified in S. suis. β-galactosidase activity and electrophoretic mobility shift assay (EMSA) revealed that Xress and the Xress-MNTss complex could bind directly to the Xress-MNTss promoter as well as downregulate streptomycin adenylyltransferase ZY05719_RS04610. Interestingly, the Xress deletion mutant was less pathogenic in vivo following a challenge in mice. Transmission electron microscopy and adhesion assays pointed to a significantly thinner capsule but greater biofilm-formation capacity in ΔXress than in the wild-type strain. These results indicate that Xress-MNTss, a new type II TA system, plays an important role in antibiotic resistance and pathogenicity in S. suis.
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Affiliation(s)
- Qibing Gu
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China.,Key Laboratory of Animal Bacteriology, Ministry of Agriculture, Nanjing, China.,OIE Reference Laboratory for Swine Streptococcosis, Nanjing, China
| | - Peijuan He
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China.,Key Laboratory of Animal Bacteriology, Ministry of Agriculture, Nanjing, China.,OIE Reference Laboratory for Swine Streptococcosis, Nanjing, China
| | - Dan Wang
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China.,Key Laboratory of Animal Bacteriology, Ministry of Agriculture, Nanjing, China.,OIE Reference Laboratory for Swine Streptococcosis, Nanjing, China
| | - Jiale Ma
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China.,Key Laboratory of Animal Bacteriology, Ministry of Agriculture, Nanjing, China.,OIE Reference Laboratory for Swine Streptococcosis, Nanjing, China
| | - Xiaojun Zhong
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China.,Key Laboratory of Animal Bacteriology, Ministry of Agriculture, Nanjing, China.,OIE Reference Laboratory for Swine Streptococcosis, Nanjing, China.,College of Animal Science and Technology, College of Veterinary Medicine, Zhejiang A&F University, Hangzhou, China
| | - Yinchu Zhu
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China.,Key Laboratory of Animal Bacteriology, Ministry of Agriculture, Nanjing, China.,OIE Reference Laboratory for Swine Streptococcosis, Nanjing, China.,Institute of Animal Husbandry and Veterinary Sciences, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
| | - Yue Zhang
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China.,Key Laboratory of Animal Bacteriology, Ministry of Agriculture, Nanjing, China.,OIE Reference Laboratory for Swine Streptococcosis, Nanjing, China.,College of Veterinary Medicine, Henan Agricultural University, Zhengzhou, China
| | - Qiankun Bai
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China.,Key Laboratory of Animal Bacteriology, Ministry of Agriculture, Nanjing, China.,OIE Reference Laboratory for Swine Streptococcosis, Nanjing, China
| | - Zihao Pan
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China.,Key Laboratory of Animal Bacteriology, Ministry of Agriculture, Nanjing, China.,OIE Reference Laboratory for Swine Streptococcosis, Nanjing, China
| | - Huochun Yao
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China.,Key Laboratory of Animal Bacteriology, Ministry of Agriculture, Nanjing, China.,OIE Reference Laboratory for Swine Streptococcosis, Nanjing, China
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12
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Kamruzzaman M, Wu AY, Iredell JR. Biological Functions of Type II Toxin-Antitoxin Systems in Bacteria. Microorganisms 2021; 9:microorganisms9061276. [PMID: 34208120 PMCID: PMC8230891 DOI: 10.3390/microorganisms9061276] [Citation(s) in RCA: 68] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Revised: 06/04/2021] [Accepted: 06/07/2021] [Indexed: 12/14/2022] Open
Abstract
After the first discovery in the 1980s in F-plasmids as a plasmid maintenance system, a myriad of toxin-antitoxin (TA) systems has been identified in bacterial chromosomes and mobile genetic elements (MGEs), including plasmids and bacteriophages. TA systems are small genetic modules that encode a toxin and its antidote and can be divided into seven types based on the nature of the antitoxin molecules and their mechanism of action to neutralise toxins. Among them, type II TA systems are widely distributed in chromosomes and plasmids and the best studied so far. Maintaining genetic material may be the major function of type II TA systems associated with MGEs, but the chromosomal TA systems contribute largely to functions associated with bacterial physiology, including the management of different stresses, virulence and pathogenesis. Due to growing interest in TA research, extensive work has been conducted in recent decades to better understand the physiological roles of these chromosomally encoded modules. However, there are still controversies about some of the functions associated with different TA systems. This review will discuss the most current findings and the bona fide functions of bacterial type II TA systems.
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Affiliation(s)
- Muhammad Kamruzzaman
- Centre for Infectious Diseases and Microbiology, The Westmead Institute for Medical Research, The University of Sydney, Westmead, NSW 2145, Australia;
- Correspondence: (M.K.); (J.R.I.)
| | - Alma Y. Wu
- Centre for Infectious Diseases and Microbiology, The Westmead Institute for Medical Research, The University of Sydney, Westmead, NSW 2145, Australia;
| | - Jonathan R. Iredell
- Centre for Infectious Diseases and Microbiology, The Westmead Institute for Medical Research, The University of Sydney, Westmead, NSW 2145, Australia;
- Westmead Hospital, Westmead, NSW 2145, Australia
- Correspondence: (M.K.); (J.R.I.)
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13
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Abstract
Toxin-antitoxin modules function in the genetic stability of mobile genetic elements, bacteriophage defense, and antibiotic tolerance. A gain-of-function mutation of the Escherichia coli K-12 hipBA module can induce antibiotic tolerance in a subpopulation of bacterial cells, a phenomenon known as persistence. HipA is a Ser/Thr kinase that phosphorylates and inactivates glutamyl tRNA synthetase, inhibiting cellular translation and inducing the stringent response. Additional characterized HipA homologues include HipT from pathogenic E. coli O127 and YjjJ of E. coli K-12, which are encoded by tricistronic hipBST and monocistronic operons, respectively. The apparent diversity of HipA homologues in bacterial genomes inspired us to investigate overall phylogeny. Here, we present a comprehensive phylogenetic analysis of the Hip kinases in bacteria and archaea that expands on this diversity by revealing seven novel kinase families. Kinases of one family, encoded by monocistronic operons, consist of an N-terminal core kinase domain, a HipS-like domain, and a HIRAN (HIP116 Rad5p N-terminal) domain. HIRAN domains bind single- or double-stranded DNA ends. Moreover, five types of bicistronic kinase operons encode putative antitoxins with HipS-HIRAN, HipS, γδ-resolvase, or Stl repressor-like domains. Finally, our analysis indicates that reversion of hipBA gene order happened independently several times during evolution.
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14
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Rosendahl S, Tamman H, Brauer A, Remm M, Hõrak R. Chromosomal toxin-antitoxin systems in Pseudomonas putida are rather selfish than beneficial. Sci Rep 2020; 10:9230. [PMID: 32513960 PMCID: PMC7280312 DOI: 10.1038/s41598-020-65504-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2020] [Accepted: 05/06/2020] [Indexed: 11/09/2022] Open
Abstract
Chromosomal toxin-antitoxin (TA) systems are widespread genetic elements among bacteria, yet, despite extensive studies in the last decade, their biological importance remains ambivalent. The ability of TA-encoded toxins to affect stress tolerance when overexpressed supports the hypothesis of TA systems being associated with stress adaptation. However, the deletion of TA genes has usually no effects on stress tolerance, supporting the selfish elements hypothesis. Here, we aimed to evaluate the cost and benefits of chromosomal TA systems to Pseudomonas putida. We show that multiple TA systems do not confer fitness benefits to this bacterium as deletion of 13 TA loci does not influence stress tolerance, persistence or biofilm formation. Our results instead show that TA loci are costly and decrease the competitive fitness of P. putida. Still, the cost of multiple TA systems is low and detectable in certain conditions only. Construction of antitoxin deletion strains showed that only five TA systems code for toxic proteins, while other TA loci have evolved towards reduced toxicity and encode non-toxic or moderately potent proteins. Analysis of P. putida TA systems' homologs among fully sequenced Pseudomonads suggests that the TA loci have been subjected to purifying selection and that TA systems spread among bacteria by horizontal gene transfer.
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Affiliation(s)
- Sirli Rosendahl
- Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
| | - Hedvig Tamman
- Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
| | - Age Brauer
- Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
| | - Maido Remm
- Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
| | - Rita Hõrak
- Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia.
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15
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Zhao Y, Li G, Yao XY, Lu SG, Wang J, Shen XD, Li M. The Impact of SsPI-1 Deletion on Streptococcus suis Virulence. Pathogens 2019; 8:pathogens8040287. [PMID: 31817637 PMCID: PMC6963714 DOI: 10.3390/pathogens8040287] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2019] [Revised: 12/03/2019] [Accepted: 12/04/2019] [Indexed: 01/26/2023] Open
Abstract
(1) Background: Streptococcus suis is an important zoonotic pathogen that infects pigs and can occasionally cause life-threatening systemic infections in humans. Two large-scale outbreaks of streptococcal toxic shock-like syndrome in China suggest that the pathogenicity of S. suis has been changing in recent years. Genetic analysis revealed the presence of a chromosomal pathogenicity island (PAI) designated SsPI-1 in Chinese epidemic S. suis strains. The purpose of this study is to define the role of SsPI-1 in the virulence of S. suis. (2) Methods: A SsPI-1 deletion mutant was compared to the wild-type strain regarding the ability to attach to epithelial cells, to cause host disease and mortality, and to stimulate host immune response in experimental infection of piglets. (3) Results: Deletion of SsPI-1 significantly reduces adherence of S. suis to epithelial cells and abolishes the lethality of the wild-type strain in piglets. The SsPI-1 mutant causes no significant pathological lesions and exhibits an impaired ability to induce proinflammatory cytokine production. (4) Conclusions: Deletion of the SsPI-1 PAI attenuates the virulence of this pathogen. We conclude that SsPI-1 is a critical contributor to the evolution of virulence in epidemic S. suis.
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Affiliation(s)
- Yan Zhao
- Department of Microbiology, College of Basic Medical Sciences, Army Medical University (Third Military Medical University), Key Laboratory of Microbial Engineering under the Educational Committee in Chongqing, Chongqing 400038, China; (Y.Z.); (G.L.); (S.-G.L.); (J.W.)
| | - Gang Li
- Department of Microbiology, College of Basic Medical Sciences, Army Medical University (Third Military Medical University), Key Laboratory of Microbial Engineering under the Educational Committee in Chongqing, Chongqing 400038, China; (Y.Z.); (G.L.); (S.-G.L.); (J.W.)
| | - Xin-Yue Yao
- Jinling Hospital Research Institute of Clinical Laboratory Medicine, Nanjing University, School of Medicine, Nanjing 210002, China;
| | - Shu-Guang Lu
- Department of Microbiology, College of Basic Medical Sciences, Army Medical University (Third Military Medical University), Key Laboratory of Microbial Engineering under the Educational Committee in Chongqing, Chongqing 400038, China; (Y.Z.); (G.L.); (S.-G.L.); (J.W.)
| | - Jing Wang
- Department of Microbiology, College of Basic Medical Sciences, Army Medical University (Third Military Medical University), Key Laboratory of Microbial Engineering under the Educational Committee in Chongqing, Chongqing 400038, China; (Y.Z.); (G.L.); (S.-G.L.); (J.W.)
| | - Xiao-Dong Shen
- Department of Biochemistry and Molecular Biology, College of Basic Medical Sciences, Army Medical University (Third Military Medical University), Chongqing 400038, China
- Correspondence: (M.L.); (X.-D.S.); Tel.: +86-23-68772241 (M.L.)
| | - Ming Li
- Department of Microbiology, College of Basic Medical Sciences, Army Medical University (Third Military Medical University), Key Laboratory of Microbial Engineering under the Educational Committee in Chongqing, Chongqing 400038, China; (Y.Z.); (G.L.); (S.-G.L.); (J.W.)
- Correspondence: (M.L.); (X.-D.S.); Tel.: +86-23-68772241 (M.L.)
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16
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Towards Exploring Toxin-Antitoxin Systems in Geobacillus: A Screen for Type II Toxin-Antitoxin System Families in a Thermophilic Genus. Int J Mol Sci 2019; 20:ijms20235869. [PMID: 31771094 PMCID: PMC6929052 DOI: 10.3390/ijms20235869] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2019] [Revised: 11/12/2019] [Accepted: 11/20/2019] [Indexed: 12/19/2022] Open
Abstract
The toxin-antitoxin (TA) systems have been attracting attention due to their role in regulating stress responses in prokaryotes and their biotechnological potential. Much recognition has been given to type II TA system of mesophiles, while thermophiles have received merely limited attention. Here, we are presenting the putative type II TA families encoded on the genomes of four Geobacillus strains. We employed the TA finder tool to mine for TA-coding genes and manually curated the results using protein domain analysis tools. We also used the NCBI BLAST, Operon Mapper, ProOpDB, and sequence alignment tools to reveal the geobacilli TA features. We identified 28 putative TA pairs, distributed over eight TA families. Among the identified TAs, 15 represent putative novel toxins and antitoxins, belonging to the MazEF, MNT-HEPN, ParDE, RelBE, and XRE-COG2856 TA families. We also identified a potentially new TA composite, AbrB-ParE. Furthermore, we are suggesting the Geobacillus acetyltransferase TA (GacTA) family, which potentially represents one of the unique TA families with a reverse gene order. Moreover, we are proposing a hypothesis on the xre-cog2856 gene expression regulation, which seems to involve the c-di-AMP. This study aims for highlighting the significance of studying TAs in Geobacillus and facilitating future experimental research.
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17
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Genome-Wide Screening for Identification of Novel Toxin-Antitoxin Systems in Staphylococcus aureus. Appl Environ Microbiol 2019; 85:AEM.00915-19. [PMID: 31375497 DOI: 10.1128/aem.00915-19] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2019] [Accepted: 07/11/2019] [Indexed: 01/24/2023] Open
Abstract
Toxin-antitoxin (TA) systems consist of toxin-inhibiting diverse cellular functions (e.g., DNA replication, transcription, and translation) and a noncoding RNA or protein antitoxin. TA systems are associated with various cellular events, such as stress responses, programmed cell death, and bacterial pathogenicity. Recent advances in genome sequencing and bioinformatics research have demonstrated that most bacteria harbor various kinds of TA modules on their chromosomes; however, there is little understanding of chromosomally encoded TA systems in the Gram-positive pathogen Staphylococcus aureus Here, we report on newly discovered S. aureus TA systems, each of which is composed of two proteins. Manual search and gene operon prediction analysis identified eight 2-gene operons as potential candidates for TA systems. Subsequently, using an Escherichia coli host killing and rescue assay, we demonstrated that four of the eight candidates worked as TA systems, designated tsaAT, tsbAT, tscAT, and tsdAT Moreover, the TsaT, TsbT, TscT, and TsdT toxins inhibited S. aureus growth, and the toxicity of TsbT was neutralized by coexpressing the tsbA gene in the native host, S. aureus Further, the bioinformatics analysis of the gene clusters revealed that TsaAT, TsbAT, TscAT, and TsdAT did not exhibit sequence similarity to known bacterial TA systems, and their homologues were present only within Staphylococcus species and not among any other bacteria. Our results further advance not only the understanding of S. aureus TA systems but also the study of unannotated TA systems in various bacterial species.IMPORTANCE Recent advances in genome sequencing and bioinformatics research have demonstrated that most pathogenic bacteria harbor a large number of chromosomally encoded toxin-antitoxin (TA) modules. However, little is known about the TA systems in S. aureus Here, we newly identified four S. aureus TA systems using a combination of manual base-by-base screening and functional analysis in E. coli Moreover, all toxins of the identified TA systems caused growth inhibition in the native host S. aureus Although the newly identified TA systems did not exhibit sequence similarity with known bacterial TA systems, their orthologues were conserved only among other Staphylococcus species, indicating their uniqueness to staphylococci. Our approach opens the possibility for studying unannotated TA systems in various bacterial species.
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18
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Moreno-Del Álamo M, Tabone M, Muñoz-Martínez J, Valverde JR, Alonso JC. Toxin ζ Reduces the ATP and Modulates the Uridine Diphosphate-N-acetylglucosamine Pool. Toxins (Basel) 2019; 11:E29. [PMID: 30634431 PMCID: PMC6356619 DOI: 10.3390/toxins11010029] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Revised: 12/21/2018] [Accepted: 01/04/2019] [Indexed: 11/20/2022] Open
Abstract
Toxin ζ expression triggers a reversible state of dormancy, diminishes the pool of purine nucleotides, promotes (p)ppGpp synthesis, phosphorylates a fraction of the peptidoglycan precursor uridine diphosphate-N-acetylglucosamine (UNAG), leading to unreactive UNAG-P, induces persistence in a reduced subpopulation, and sensitizes cells to different antibiotics. Here, we combined computational analyses with biochemical experiments to examine the mechanism of toxin ζ action. Free ζ toxin showed low affinity for UNAG. Toxin ζ bound to UNAG hydrolyzed ATP·Mg2+, with the accumulation of ADP, Pi, and produced low levels of phosphorylated UNAG (UNAG-P). Toxin ζ, which has a large ATP binding pocket, may temporally favor ATP binding in a position that is distant from UNAG, hindering UNAG phosphorylation upon ATP hydrolysis. The residues D67, E116, R158 and R171, involved in the interaction with metal, ATP, and UNAG, were essential for the toxic and ATPase activities of toxin ζ; whereas the E100 and T128 residues were partially dispensable. The results indicate that ζ bound to UNAG reduces the ATP concentration, which indirectly induces a reversible dormant state, and modulates the pool of UNAG.
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Affiliation(s)
- María Moreno-Del Álamo
- Department of Microbial Biotechnology, Centro Nacional de Biotecnología, CNB-CSIC, 3 Darwin Str., 28049 Madrid, Spain.
| | - Mariangela Tabone
- Department of Microbial Biotechnology, Centro Nacional de Biotecnología, CNB-CSIC, 3 Darwin Str., 28049 Madrid, Spain.
| | - Juan Muñoz-Martínez
- Scientific Computing Service, Centro Nacional de Biotecnología, CNB-CSIC, 3 Darwin Str., 28049 Madrid, Spain.
| | - José R Valverde
- Scientific Computing Service, Centro Nacional de Biotecnología, CNB-CSIC, 3 Darwin Str., 28049 Madrid, Spain.
| | - Juan C Alonso
- Department of Microbial Biotechnology, Centro Nacional de Biotecnología, CNB-CSIC, 3 Darwin Str., 28049 Madrid, Spain.
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19
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Xu J, Zhang N, Cao M, Ren S, Zeng T, Qin M, Zhao X, Yuan F, Chen H, Bei W. Identification of Three Type II Toxin-Antitoxin Systems in Streptococcus suis Serotype 2. Toxins (Basel) 2018; 10:toxins10110467. [PMID: 30428568 PMCID: PMC6266264 DOI: 10.3390/toxins10110467] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Revised: 11/06/2018] [Accepted: 11/07/2018] [Indexed: 01/15/2023] Open
Abstract
Type II toxin-antitoxin (TA) systems are highly prevalent in bacterial genomes and have been extensively studied. These modules involve in the formation of persistence cells, the biofilm formation, and stress resistance, which might play key roles in pathogen virulence. SezAT and yefM-yoeB TA modules in Streptococcus suis serotype 2 (S. suis 2) have been studied, although the other TA systems have not been identified. In this study, we investigated nine putative type II TA systems in the genome of S. suis 2 strain SC84 by bioinformatics analysis and identified three of them (two relBE loci and one parDE locus) that function as typical type II TA systems. Interestingly, we found that the introduction of the two RelBE TA systems into Escherichia coli or the induction of the ParE toxin led to cell filamentation. Promoter activity assays indicated that RelB1, RelB2, ParD, and ParDE negatively autoregulated the transcriptions of their respective TA operons, while RelBE2 positively autoregulated its TA operon transcription. Collectively, we identified three TA systems in S. suis 2, and our findings have laid an important foundation for further functional studies on these TA systems.
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Affiliation(s)
- Jiali Xu
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
| | - Nian Zhang
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
| | - Manman Cao
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
| | - Sujing Ren
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
| | - Ting Zeng
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
| | - Minglu Qin
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
| | - Xigong Zhao
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
| | - Fangyan Yuan
- Key Laboratory of Prevention and Control Agents for Animal Bacteriosis, Institute of Animal Husbandry and Veterinary Sciences, Hubei Academy of Agricultural Sciences, Wuhan 430064, China.
| | - Huanchun Chen
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
| | - Weicheng Bei
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
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20
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Zheng F, Shao ZQ, Hao X, Wu Q, Li C, Hou H, Hu D, Wang C, Pan X. Identification of oligopeptide-binding protein (OppA) and its role in the virulence of Streptococcus suis serotype 2. Microb Pathog 2018; 118:322-329. [DOI: 10.1016/j.micpath.2018.03.061] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2017] [Revised: 03/12/2018] [Accepted: 03/30/2018] [Indexed: 01/02/2023]
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21
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The ng_ζ1 toxin of the gonococcal epsilon/zeta toxin/antitoxin system drains precursors for cell wall synthesis. Nat Commun 2018; 9:1686. [PMID: 29703974 PMCID: PMC5923241 DOI: 10.1038/s41467-018-03652-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2017] [Accepted: 03/02/2018] [Indexed: 01/14/2023] Open
Abstract
Bacterial toxin–antitoxin complexes are emerging as key players modulating bacterial physiology as activation of toxins induces stasis or programmed cell death by interference with vital cellular processes. Zeta toxins, which are prevalent in many bacterial genomes, were shown to interfere with cell wall formation by perturbing peptidoglycan synthesis in Gram-positive bacteria. Here, we characterize the epsilon/zeta toxin–antitoxin (TA) homologue from the Gram-negative pathogen Neisseria gonorrhoeae termed ng_ɛ1 / ng_ζ1. Contrary to previously studied streptococcal epsilon/zeta TA systems, ng_ɛ1 has an epsilon-unrelated fold and ng_ζ1 displays broader substrate specificity and phosphorylates multiple UDP-activated sugars that are precursors of peptidoglycan and lipopolysaccharide synthesis. Moreover, the phosphorylation site is different from the streptococcal zeta toxins, resulting in a different interference with cell wall synthesis. This difference most likely reflects adaptation to the individual cell wall composition of Gram-negative and Gram-positive organisms but also the distinct involvement of cell wall components in virulence. Toxin–antitoxin (TA) systems are important modulators of bacterial physiology. Here, the authors structurally characterize the epsilon/zeta TA system from the Gram-negative pathogen Neisseria gonorrhoeae and show that the toxin interferes with peptidoglycan and lipopolysaccharide synthesis by phosphorylating the UDP-activated sugar-precursors.
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22
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Zheng C, Zhao X, Zeng T, Cao M, Xu J, Shi G, Li J, Chen H, Bei W. Identification of four type II toxin-antitoxin systems in Actinobacillus pleuropneumoniae. FEMS Microbiol Lett 2018. [PMID: 28637172 DOI: 10.1093/femsle/fnx126] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Toxin-antitoxin (TA) systems are small genetic elements that are widely prevalent in the genomes of bacteria and archaea. These modules have been identified in various bacteria and proposed to play an important role in bacterial physiology and virulence. However, their presence in the genomes of Actinobacillus species has received no attention. In this study, we describe the identification of four type II TA systems in Actinobacillus pleuropneumoniae, the causative agent of porcine pleuropneumonia. Reverse transcription PCR analysis revealed that the genes encoding the toxin and antitoxin are co-transcribed. Overexpression of each toxin inhibited the growth of Escherichia coli, and the toxic effect could be counteracted by its cognate antitoxin. The pull-down experiments demonstrated that each toxin interacts with its cognate antitoxin in vivo. The promoter activity assays showed that each antitoxin could autoregulate either positively or negatively the TA operon transcription. In addition, the APJL_0660/0659 TA system is present in half of the detected serovars of A. pleuropneumoniae, while the others are present in all. Collectively, we identified four type II TA systems in A. pleuropneumoniae, and this study has laid the foundation for further functional study of these TA systems.
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Affiliation(s)
- Chengkun Zheng
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.,The Cooperative Innovation Center for Sustainable Pig Production, Huazhong Agricultural University, Wuhan 430070, China.,Key Laboratory of Development of Veterinary Diagnostic Products, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China
| | - Xigong Zhao
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.,The Cooperative Innovation Center for Sustainable Pig Production, Huazhong Agricultural University, Wuhan 430070, China.,Key Laboratory of Development of Veterinary Diagnostic Products, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China
| | - Ting Zeng
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.,The Cooperative Innovation Center for Sustainable Pig Production, Huazhong Agricultural University, Wuhan 430070, China.,Key Laboratory of Development of Veterinary Diagnostic Products, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China
| | - Manman Cao
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.,The Cooperative Innovation Center for Sustainable Pig Production, Huazhong Agricultural University, Wuhan 430070, China.,Key Laboratory of Development of Veterinary Diagnostic Products, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China
| | - Jiali Xu
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.,The Cooperative Innovation Center for Sustainable Pig Production, Huazhong Agricultural University, Wuhan 430070, China.,Key Laboratory of Development of Veterinary Diagnostic Products, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China
| | - Guolin Shi
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.,The Cooperative Innovation Center for Sustainable Pig Production, Huazhong Agricultural University, Wuhan 430070, China.,Key Laboratory of Development of Veterinary Diagnostic Products, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China
| | - Jinquan Li
- College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, China
| | - Huanchun Chen
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.,The Cooperative Innovation Center for Sustainable Pig Production, Huazhong Agricultural University, Wuhan 430070, China.,Key Laboratory of Development of Veterinary Diagnostic Products, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China
| | - Weicheng Bei
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.,The Cooperative Innovation Center for Sustainable Pig Production, Huazhong Agricultural University, Wuhan 430070, China.,Key Laboratory of Development of Veterinary Diagnostic Products, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China
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23
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Jurėnas D, Garcia-Pino A, Van Melderen L. Novel toxins from type II toxin-antitoxin systems with acetyltransferase activity. Plasmid 2017; 93:30-35. [PMID: 28941941 DOI: 10.1016/j.plasmid.2017.08.005] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Revised: 08/24/2017] [Accepted: 08/28/2017] [Indexed: 12/21/2022]
Abstract
Type II toxin-antitoxin (TA) systems are widespread in bacterial and archeal genomes. These modules are very dynamic and participate in bacterial genome evolution through horizontal gene transfer. TA systems are commonly composed of a labile antitoxin and a stable toxin. Toxins appear to preferentially inhibit the protein synthesis process. Toxins use a variety of molecular mechanisms and target nearly every step of translation to achieve their inhibitory function. This review focuses on a recently identified TA family that includes acetyltransferase toxins. The AtaT and TacT toxins are the best-characterized to date in this family. AtaT and TacT both inhibit translation by acetylating the amino acid charged on tRNAs. However, the specificities of these 2 toxins are different as AtaT inhibits translation initiation by acetylation of the initiator tRNA whereas TacT acetylates elongator tRNAs. The molecular mechanisms of these toxins are discussed, as well as the functions and possible evolutionary origins of this diverse toxin family.
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Affiliation(s)
- Dukas Jurėnas
- Department of Biochemistry and Molecular Biology, Vilnius University Joint Life Sciences Center, Vilnius, Lithuania; Cellular and Molecular Microbiology (CM2), Faculté des Sciences, Université Libre de Bruxelles (ULB), Belgium
| | - Abel Garcia-Pino
- Cellular and Molecular Microbiology (CM2), Faculté des Sciences, Université Libre de Bruxelles (ULB), Belgium
| | - Laurence Van Melderen
- Cellular and Molecular Microbiology (CM2), Faculté des Sciences, Université Libre de Bruxelles (ULB), Belgium.
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24
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Lu Y, Yan H, Deng J, Huang Z, Jin X, Yu Y, Hu Q, Hu F, Wang J. Development and evaluation of an efficient heterologous gene knock-in reporter system in Lactococcus lactis. Microb Cell Fact 2017; 16:154. [PMID: 28923077 PMCID: PMC5604289 DOI: 10.1186/s12934-017-0770-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Accepted: 09/09/2017] [Indexed: 02/07/2023] Open
Abstract
Background Lactococcus lactis is a food grade probiotics and widely used to express heterologous proteins. Generally, target genes are knocked into the L. lactis genome through double-crossover recombination to express heterologous proteins stably. However, creating marker-less heterologous genes knocked-in clones is laborious. In this study, an efficient heterologous gene knock-in reporter system was developed in L. lactis NZ9000. Results Our knock-in reporter system consists of a temperature-sensitive plasmid pJW and a recombinant L. lactis strain named NZB. The pJW contains homologous arms, and was constructed to knock-in heterologous genes at a fixed locus of NZ9000 genome. lacZ (β-galactosidase) gene was knocked into the chromosome of NZ9000 as a counter-selective marker through the plasmid pJW to generate NZB. The engineered NZB strain formed blue colonies on X-Gal plate. The desired double-crossover mutants formed white colonies distinctive from the predominantly blue colonies (parental and plasmid-integrated clones) when the embedded lacZ was replaced with the target heterologous genes carried by pJW in NZB. Conclusions By using the system, the heterologous gene knocked-in clones are screened by colony phenotype change rather than by checking colonies individually. Our new knock-in reporter system provides an efficient method to create heterologous genes knocked-in clones. Electronic supplementary material The online version of this article (doi:10.1186/s12934-017-0770-1) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Yifei Lu
- Department of Microbiology, Third Military Medical University, Chongqing, 400038, China
| | - Hongxiang Yan
- Department of Microbiology, Third Military Medical University, Chongqing, 400038, China
| | - Jiezhong Deng
- Department of Microbiology, Third Military Medical University, Chongqing, 400038, China
| | - Zhigang Huang
- Department of Microbiology, Third Military Medical University, Chongqing, 400038, China
| | - Xurui Jin
- Department of Microbiology, Third Military Medical University, Chongqing, 400038, China
| | - Yanlan Yu
- Department of Microbiology, Third Military Medical University, Chongqing, 400038, China
| | - Qiwen Hu
- Department of Microbiology, Third Military Medical University, Chongqing, 400038, China
| | - Fuquan Hu
- Department of Microbiology, Third Military Medical University, Chongqing, 400038, China
| | - Jing Wang
- Department of Microbiology, Third Military Medical University, Chongqing, 400038, China.
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Díaz-Orejas R, Espinosa M, Yeo CC. The Importance of the Expendable: Toxin-Antitoxin Genes in Plasmids and Chromosomes. Front Microbiol 2017; 8:1479. [PMID: 28824602 PMCID: PMC5543033 DOI: 10.3389/fmicb.2017.01479] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2017] [Accepted: 07/24/2017] [Indexed: 02/01/2023] Open
Abstract
Toxin–antitoxin (TA) genes were first reported in plasmids and were considered expendable genetic cassettes involved in the stable maintenance of the plasmid replicon by interfering with growth and/or viability of bacteria in which the plasmid was lost. TAs were later found in bacterial chromosomes and also in integrated mobile genetic elements; they were proposed to be involved in the bacterial response to stressful situations. At present, 100s of TAs have been identified and classified in up to six families (I to VI), with those belonging to the type II (constituted by two protein components) being the most studied. Based on well-characterized examples of several type II TAs, we discuss in this review that irrespective of their locations in plasmids or chromosomes, TAs functionally overlap as indicated by: (i) in both locations they can mediate the maintenance of genetic elements to which they are physical linked, and (ii) they can induce persistence or virulence in response to stress situations. Examples of functional confluences in homologous TA systems with different locations are also given. We also consider whether the physiological role of TAs is due to their genetic organization as operons or to their inherent properties, like the short lifespan of the antitoxin component.
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Affiliation(s)
- Ramón Díaz-Orejas
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas (CSIC)Madrid, Spain
| | - Manuel Espinosa
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas (CSIC)Madrid, Spain
| | - Chew Chieng Yeo
- Faculty of Medicine, Biomedical Research Centre, Universiti Sultan Zainal AbidinKuala Terengganu, Malaysia
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Li M, Shen X, Zhao Y, Hu X, Hu F, Rao X. Better understanding of homologous recombination through a 12-week laboratory course for undergraduates majoring in biotechnology. BIOCHEMISTRY AND MOLECULAR BIOLOGY EDUCATION : A BIMONTHLY PUBLICATION OF THE INTERNATIONAL UNION OF BIOCHEMISTRY AND MOLECULAR BIOLOGY 2017; 45:329-335. [PMID: 28314074 DOI: 10.1002/bmb.21043] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Revised: 11/08/2016] [Accepted: 12/23/2016] [Indexed: 06/06/2023]
Abstract
Homologous recombination, a central concept in biology, is defined as the exchange of DNA strands between two similar or identical nucleotide sequences. Unfortunately, undergraduate students majoring in biotechnology often experience difficulties in understanding the molecular basis of homologous recombination. In this study, we developed and implemented a 12-week laboratory course for biotechnology undergraduates in which gene targeting in Streptococcus suis was used to facilitate their understanding of the basic concept and process of homologous recombination. Students worked in teams of two to select a gene of interest to create a knockout mutant using methods that relied on homologous recombination. By integrating abstract knowledge and practice in the process of scientific research, students gained hands-on experience in molecular biology techniques while learning about the principle and process of homologous recombination. The learning outcomes and survey-based assessment demonstrated that students substantially enhanced their understanding of how homologous recombination could be used to study gene function. Overall, the course was very effective for helping biotechnology undergraduates learn the theory and application of homologous recombination, while also yielding positive effects in developing confidence and scientific skills for future work in research. © 2017 by The International Union of Biochemistry and Molecular Biology, 45(4):329-335, 2017.
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Affiliation(s)
- Ming Li
- Department of Microbiology, Third Military Medical University, Chongqing, China
| | - Xiaodong Shen
- Department of Biochemistry and Molecular Biology, Third Military Medical University, Chongqing, China
| | - Yan Zhao
- Department of Microbiology, Third Military Medical University, Chongqing, China
| | - Xiaomei Hu
- Department of Microbiology, Third Military Medical University, Chongqing, China
| | - Fuquan Hu
- Department of Microbiology, Third Military Medical University, Chongqing, China
| | - Xiancai Rao
- Department of Microbiology, Third Military Medical University, Chongqing, China
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Chan WT, Espinosa M. The Streptococcus pneumoniae pezAT Toxin-Antitoxin System Reduces β-Lactam Resistance and Genetic Competence. Front Microbiol 2016; 7:1322. [PMID: 27610103 PMCID: PMC4997998 DOI: 10.3389/fmicb.2016.01322] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Accepted: 08/10/2016] [Indexed: 12/11/2022] Open
Abstract
Chromosomally encoded Type II Toxin–Antitoxin operons are ubiquitous in bacteria and archaea. Antitoxins neutralize the toxic effect of cognate Toxins by protein–protein interactions and sequestering the active residues of the Toxin. Toxins target essential bacterial processes, mostly translation and replication. However, one class apart is constituted by the PezAT pair because the PezT toxin target cell wall biosynthesis. Here, we have examined the role of the pezAT toxin–antitoxin genes in its natural host, the pathogenic bacterium Streptococcus pneumoniae. The pezAT operon on Pneumococcal Pathogenicity Island 1 was deleted from strain R6 and its phenotypic traits were compared with those of the wild type. The mutant cells formed shorter chains during exponential phase, leading to increased colony-forming units. At stationary phase, the mutant was more resilient to lysis. Importantly, the mutant exhibited higher resistance to antibiotics targeting cell walls (β-lactams), but not to antibiotics acting at other levels. In addition, the mutants also showed enhanced genetic competence. We suggest that PezAT participates in a subtle equilibrium between loss of functions (resistance to β-lactams and genetic competence) and gain of other traits (virulence).
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Affiliation(s)
- Wai T Chan
- Bacterial Gene Expression and Gene Transfer, Molecular Microbiology and Infectious Biology, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas Madrid, Spain
| | - Manuel Espinosa
- Bacterial Gene Expression and Gene Transfer, Molecular Microbiology and Infectious Biology, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas Madrid, Spain
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Functional definition of BirA suggests a biotin utilization pathway in the zoonotic pathogen Streptococcus suis. Sci Rep 2016; 6:26479. [PMID: 27217336 PMCID: PMC4877710 DOI: 10.1038/srep26479] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Accepted: 05/04/2016] [Indexed: 11/30/2022] Open
Abstract
Biotin protein ligase is universal in three domains of life. The paradigm version of BPL is the Escherichia coli BirA that is also a repressor for the biotin biosynthesis pathway. Streptococcus suis, a leading bacterial agent for swine diseases, seems to be an increasingly-important opportunistic human pathogen. Unlike the scenario in E. coli, S. suis lacks the de novo biotin biosynthesis pathway. In contrast, it retains a bioY, a biotin transporter-encoding gene, indicating an alternative survival strategy for S. suis to scavenge biotin from its inhabiting niche. Here we report functional definition of S. suis birA homologue. The in vivo functions of the birA paralogue with only 23.6% identity to the counterpart of E. coli, was judged by its ability to complement the conditional lethal mutants of E. coli birA. The recombinant BirA protein of S. suis was overexpressed in E. coli, purified to homogeneity and verified with MS. Both cellulose TLC and MALDI-TOFF-MS assays demonstrated that the S. suis BirA protein catalyzed the biotinylation reaction of its acceptor biotin carboxyl carrier protein. EMSA assays confirmed binding of the bioY gene to the S. suis BirA. The data defined the first example of the bifunctional BirA ligase/repressor in Streptococcus.
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Li G, Shen M, Lu S, Le S, Tan Y, Wang J, Zhao X, Shen W, Guo K, Yang Y, Zhu H, Rao X, Hu F, Li M. Identification and Characterization of the HicAB Toxin-Antitoxin System in the Opportunistic Pathogen Pseudomonas aeruginosa. Toxins (Basel) 2016; 8:113. [PMID: 27104566 PMCID: PMC4848639 DOI: 10.3390/toxins8040113] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Revised: 04/06/2016] [Accepted: 04/08/2016] [Indexed: 12/26/2022] Open
Abstract
Toxin-antitoxin (TA) systems are small genetic modules that are widely distributed in the genomes of bacteria and archaea and have been proposed to fulfill numerous functions. Here, we describe the identification and characterization of a type II TA system, comprising the hicAB locus in the human opportunistic pathogen Pseudomonas aeruginosa. The hicAB locus consists of genes hicA and hicB encoding a toxin and its cognate antitoxin, respectively. BLAST analysis revealed that hicAB is prevalent in approximately 36% of P. aeruginosa strains and locates in the same genomic region. RT-PCR demonstrated that hicAB forms a bicistronic operon that is cotranscribed under normal growth conditions. Overproduction of HicA inhibited the growth of Escherichia coli, and this effect could be counteracted by co-expression of HicB. The Escherichia coli kill/rescue assay showed that the effect of HicA is bacteriostatic, rather than bactericidal. Deletion of hicAB had no effect on the biofilm formation and virulence of P. aeruginosa in a mice infection model. Collectively, this study presents the first characterization of the HicAB system in the opportunistic pathogen P. aeruginosa.
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Affiliation(s)
- Gang Li
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Mengyu Shen
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Shuguang Lu
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Shuai Le
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Yinling Tan
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Jing Wang
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Xia Zhao
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Wei Shen
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Keke Guo
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Yuhui Yang
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Hongbin Zhu
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Xiancai Rao
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Fuquan Hu
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Ming Li
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
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