Analysis of the Bacillus cereus SpoIIS antitoxin-toxin system reveals its three-component nature

Abstract

Programmed cell death in bacteria is generally associated with two-component toxin-antitoxin systems. The SpoIIS toxin-antitoxin system, consisting of a membrane-bound SpoIISA toxin and a small, cytosolic antitoxin SpoIISB, was originally identified in Bacillus subtilis. In this work we describe the Bacillus cereus SpoIIS system which is a three-component system, harboring an additional gene spoIISC. Its protein product serves as an antitoxin, and similarly as SpoIISB, is able to bind SpoIISA and abolish its toxic effect. Our results indicate that SpoIISC seems to be present not only in B. cereus but also in other Bacilli containing a SpoIIS toxin-antitoxin system. In addition, we show that B. cereus SpoIISA can form higher oligomers and we discuss the possible role of this multimerization for the protein's toxic function.

Keeping the Wolves at Bay: Antitoxins of Prokaryotic Type II Toxin-Antitoxin Systems

“… Genetic organization of tripartite type II TA systems . The tripartite TA systems depicted here are the pasABC TA system of plasmid pTF-FC2 from A. ferroxidans (Smith and Rawlings, 1997 ), the ω-ε-ζ TA system of plasmid pSM19035 from S. pyogenes (Cegłowski et al, 1993 ), the paaR2-paaA2-parE2 system from E. coli O157:H7 (Hallez et al, 2010 ), and the spoIIS TA system from B. cereus (Melničáková et al, 2015 ). The antitoxin gene is depicted as blue arrows, the toxin gene as red arrows, the regulatory or third component gene as yellow arrows while gray arrows are for surrounding non-TA genes.…”

“…A recent report regarding the SpoIIS TA system from Bacillus cereus revealed a curious variation of the tripartite TA system (Melničáková et al, 2015 ). The spoIIS locus was initially identified in B. subtilis and was then deduced to consist of two genes, the spoIISA toxin-coding gene and the spoIISB antitoxin-coding gene, i.e., a typical type II TA locus (Adler et al, 2001 ).…”

“…The spoIIS locus was initially identified in B. subtilis and was then deduced to consist of two genes, the spoIISA toxin-coding gene and the spoIISB antitoxin-coding gene, i.e., a typical type II TA locus (Adler et al, 2001 ). However, transcriptome analysis of B. subtilis had indicated the presence of a third transcriptionally active region within the spoIIS locus designated S458 (Nicolas et al, 2012 ) and which has been renamed spoIISC (Melničáková et al, 2015 ). Intriguingly, it was discovered that spoIISC in B. subtilis as well as B. cereus coded for an antitoxin that neutralizes the toxicity of SpoIISA.…”

“…Intriguingly, it was discovered that spoIISC in B. subtilis as well as B. cereus coded for an antitoxin that neutralizes the toxicity of SpoIISA. In other words, the SpoIISA toxin is neutralized by two antitoxins, SpoIISB and SpoIISC (Melničáková et al, 2015 ). In a departure from most type II TA systems, each gene in the spoIIS locus is transcribed from its own promoter (Figure 6 ) and each promoter is apparently transcribed under different conditions.…”

“…In a departure from most type II TA systems, each gene in the spoIIS locus is transcribed from its own promoter (Figure 6 ) and each promoter is apparently transcribed under different conditions. For example, in B. subitilis only spoIISA and spoIISB are transcribed during nutrient deprivation, whereas during ethanol stress, only the spoIISA is transcribed and spoIISC transcribed during biofilm formation (Nicolas et al, 2012 ; Melničáková et al, 2015 ). This gives a hint at the complexity of the regulation of the spoIIS locus that may necessitate the need for two antitoxins, each of which could antagonize the toxicity of SpoIISA.…”