Spore formation by the bacterium Bacillus subtilis is an elaborate developmental process that is triggered by nutrient limitation. Cells that have entered the pathway to sporulate produce and export a killing factor and a signaling protein that act cooperatively to block sister cells from sporulating and to cause them to lyse. The sporulating cells feed on the nutrients thereby released, which allows them to keep growing rather than to complete morphogenesis. Entry into sporulation is governed by the regulatory protein Spo0A (master regulator of sporulation) [1]. Upon Spo0A phosphorylation, it represses the expression of abrB, a negative regulator of skfABCEFGH and sdpAB, leading to the transcriptional activation of sdpAB operon. The production of SdpAB is essential for the SDP toxin. SDP is a 42-amino-acid, ribosomally synthesized AMP which contains a disulfide bond between two cysteine residues located at the N terminus [2]. SDP acts by rapidly collapsing the proton motive force thereby inducing autolysin mediated lysis on neighboring species and non-biofilm producing B. subtilis cells (which do not produce SdpI) to respond by moving away, while autolysis would release nutrients that can be readily used to promote biofilm growth [3]. SdpAB proteins are required to produce SDP from SdpC33-203. This domain family is found in SdpA proteins which are predicted to be a 158-amino-acid proteins suggest to be primarily cytoplasmic [2].

1: Cannibalism by sporulating bacteria. Gonzalez-Pastor JE, Hobbs EC, Losick R; Science. 2003;301:510-513. PMID:12817086

2: Production of the cannibalism toxin SDP is a multistep process that requires SdpA and SdpB. Perez Morales TG, Ho TD, Liu WT, Dorrestein PC, Ellermeier CD; J Bacteriol. 2013;195:3244-3251. PMID:23687264

3: The Bacillus subtilis cannibalism toxin SDP collapses the proton motive force and induces autolysis. Lamsa A, Liu WT, Dorrestein PC, Pogliano K; Mol Microbiol. 2012;84:486-500. PMID:22469514