Immunity protein that provides protection for the cell against the toxic effects of SDP, its own SdpC-derived killing factor, and that functions as a receptor/signal transduction protein as well. Once SDP accumulates in the extracellular milieu, SdpI binds to SDP, causing sequestration of SdpR at the bacterial membrane. By Spo0A during nutrient starvation, through its direct negative control of AbrB, repressed by AbrB during regular growth when nutrients are plentiful, and also by SdpR (PubMed:16469701). Induced by expression of SDP (active peptide of sdpC) (PubMed:16469701, PubMed:23687264). Results in increased SigW expression which is dependent on SdpC. Results in weaker growth (70% of wild-type cell density) on LB medium, with more pronounced effects on sporulation medium (15% of wild-type). Concomitant deletion of SigW results in greatly diminished growth (5% of wild-type on LB and 3% on sporulation medium). Over time, single SdpI mutant stops growing on sporulation medium, while the SdpI SigW double mutant eventually lyses. Deletion of RsiW restores growth of the SdpI single mutant to near wild-type levels. I'll have you for supper - Issue 90 of January 2008