Characteristic and role of chromosomal type II toxin-antitoxin systems locus in Enterococcus faecalis ATCC29212
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Characteristic and role of chromosomal type II toxin-antitoxin systems locus in Enterococcus faecalis ATCC29212§ Zhen Li1*, Chao Shi2, Shanjun Gao1, Xiulei Zhang1, Di Lu1, and Guangzhi Liu1 1
Microbiome Laboratory, Henan Provincial People’s Hospital, Zhengzhou University People’s Hospital, Zhengzhou, Henan 450003, P. R. China 2 Department of Molecular Pathology, The Affiliated Cancer Hospital of Zhengzhou University, Zhengzhou, Henan 450008, P. R. China (Received Feb 12, 2020 / Revised Aug 31, 2020 / Accepted Sep 18, 2020)
The Gram-positive bacterium Enterococcus faecalis is currently one of the major pathogens of nosocomial infections. The lifestyle of E. faecalis relies primarily on its remarkable capacity to face and survive in harsh environmental conditions. Toxin-antitoxin (TA) systems have been linked to the growth control of bacteria in response to adverse environments but have rarely been reported in Enterococcus. Three functional type II TA systems were identified among the 10 putative TA systems encoded by E. faecalis ATCC29212. These toxin genes have conserved domains homologous to MazF (DR75_ 1948) and ImmA/IrrE family metallo-endopeptidases (DR75_ 1673 and DR75_2160). Overexpression of toxin genes could inhibit the growth of Escherichia coli. However, the toxin DR75_1673 could not inhibit bacterial growth, and the bacteriostatic effect occurred only when it was coexpressed with the antitoxin DR75_1672. DR75_1948–DR75_1949 and DR75_ 160–DR75_2161 could maintain the stable inheritance of the unstable plasmid pLMO12102 in E. coli. Moreover, the transcription levels of these TAs showed significant differences when cultivated under normal conditions and with different temperatures, antibiotics, anaerobic agents and H2O2. When DR75_2161 was knocked out, the growth of the mutant strain at high temperature and oxidative stress was limited. The experimental characterization of these TAs loci might be helpful to investigate the key roles of type II TA systems in the physiology and environmental stress responses of Enterococcus. Keywords: Enterococcus faecalis, toxin-antitoxin system, plasmid stability, environmental stress Introduction Enterococci, which are commensal Gram-positive facultative *For correspondence. E-mail: [email protected] § Supplemental material for this article may be found at http://www.springerlink.com/content/120956. Copyright ⓒ 2020, The Microbiological Society of Korea
anaerobic bacteria, are considered to be the third most frequent cause of hospital-acquired infections and a major threat to public health due to the alarming rise in multidrug-resistant isolates(Gao et al., 2018). Enterococcal infections in humans are mainly caused by Enterococcus faecalis and E. faecium, with the great majority of infections (~70%) caused by E. faecalis. Enterococcus faecalis can cause urethral, abdominal cavity, wound, and root canal infections in humans. In severe cases, it can lead to sepsis and infective endocarditis (Tendolkar et al., 2003; García-Solache and Rice,
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