Abstract
Toxin-antitoxin (TA) systems are ubiquitous and abundant genetic elements in bacteria and archaea. Most previous TA studies have focused on commensal and pathogenic bacteria, but have rarely focused on marine bacteria, especially those isolated from the deep sea. Here, we identified and characterized three putative TA pairs in the deep-sea-derived Streptomyces sp. strain SCSIO 02999. Our results showed that Orf5461/Orf5462 and Orf2769/Orf2770 are bona fide TA pairs. We provide several lines of evidence to demonstrate that Orf5461 and Orf5462 constitute a type-II TA pair that are homologous to the YoeB/YefM TA pair from Escherichia coli. Although YoeB from SCSIO 02999 was toxic to an E. coli host, the homologous YefM antitoxin from SCSIO 02999 did not neutralize the toxic effect of YoeB from E. coli. For the Orf2769/Orf2770 TA pair, Orf2769 overexpression caused significant cell elongation and could lead to cell death in E. coli, and the neighboring Orf2770 could neutralize the toxic effect of Orf2769. However, no homologous toxin or antitoxin was found for this pair, and no direct interaction was found between Orf2769 and Orf2770. These results suggest that Orf2769 and Orf2770 may constitute a novel TA pair. Thus, deep-sea bacteria harbor typical and novel TA pairs. The biochemical and physiological functions of different TAs in deep-sea bacteria warrant further investigation.
Highlights
Toxin-antitoxin (TA) systems are ubiquitous genetic elements that consist of a toxin and an antitoxin that neutralize the cognate toxin [1,2]
More than 37 TA systems have been identified in E. coli K-12 MG1655 [1]
TA systems have been identified in some major pathogens, such as Streptococcus pneumonia [5], Mycobacterium tuberculosis [6], Salmonella [7], and Pseudomonas aeruginosa [8,9,10]
Summary
Toxin-antitoxin (TA) systems are ubiquitous genetic elements that consist of a toxin and an antitoxin that neutralize the cognate toxin [1,2]. Most of the TAs are well studied in E. coli, TAs with new functions and characteristics have recently been discovered in other microorganisms. The type-III TAs ToxI/ToxN were first characterized in the Erwinia carotovora subspecies atroseptica [11] and the toxin ToxN acts as an endoribonuclease [12]. TA pair VapC/VapB from a deep-sea Streptomyces sp. New types of TA systems or toxins with novel functions remain to be identified in extreme marine environments. We have previously characterized a type-II TA pair VapC/VapB in SCSIO 02999 [23]. Orf5461/Orf5462 is homologous to the type-II YoeB/YefM TA pair in E. coli. Further studies are needed to explore the physiological functions of different TA systems in deep-sea bacteria
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