9.B.139 The Pmf-dissipating Cannibalism Toxin SdpC (SdpC) Family Bacillus subtilis SDP (SdpC) is a peptide toxin that kills cells outside the biofilm to support continued growth. Purified SDP, like endogenously produced SDP, delays sporulation, and the SdpI immunity protein (TC# 9.A.32.1.1) confers SDP resistance. SDP kills a variety of Gram-positive Firmicutes as well as Escherichia coli with a compromised outer membrane, suggesting that it participates in defence of the B. subtilis biofilm against cannibalism and kills other Gram-positive bacteria. Fluorescence microscopy revealed that the effect of SDP on cells differs from that of nisin, nigericin, valinomycin and vancomycin-KCl but resembles that of CCCP, DNP and azide by rapidly collapsing the pmf. It may function as a proton channel or carrier. Loss of the pmf triggers the slower process of autolysis (Lamsa et al. 2012). This secondary consequence of SDP treatment is not required for cell death since an autolysin-defective lytC, lytD, lytE, lytF strain failed to lyse but is nevertheless killed by SDP. The mechanism of pmf collapse is unknown, but collapsing it is an ideal mechanism for a toxin involved in cannibalism and biofilm defence, since this would incapacitate neighbouring cells by inhibiting motility and secretion of proteins and toxins and by inducing autolysis, thereby releasing nutrients that promote biofilm growth. May be distantly related to proponicin F (255 aas) and other members of TC family 9.B.86.
References:
Kobayashi, K. and Y. Ikemoto. (2019). Biofilm-associated toxin and extracellular protease cooperatively suppress competitors in Bacillus subtilis biofilms. PLoS Genet 15: e1008232.
Lamsa, A., W.T. Liu, P.C. Dorrestein, and K. Pogliano. (2012). The Bacillus subtilis cannibalism toxin SDP collapses the proton motive force and induces autolysis. Mol. Microbiol. 84: 486-500.
Examples:
TC#	Name	Organismal Type	Example
9.B.139.1.1	The cannibalism peptide toxin, SDP (SdpC) of 202 aas and 2 TMSs, N- and C-terminal. It may be proteolytically processed to yield the active toxin which may function as a proton channel or carrier (Lamsa et al. 2012).	Firmicutes	SdpC of Bacillus subtilis

9.B.139.1.2	SdpC homologue of 215 aas and 2 TMSs	Actinobacteria	*SdpC of Streptomyces* sp. Sirex AA-E**

9.B.139.1.3	SdpC homologue of 223 aas and 2 TMSs	Actinobacteria	SdpC homologue in Tsukamurella paurometabola

9.B.139.1.4	SdpC homologue of 196 aas	Firmicutes	SdpC homologue of Bacillus amyloliquefaciens

9.B.139.1.5	SdpC homologue of 206 aas	Firmicutes	SdpC homologue of Bacillus thuringiensis

9.B.139.1.6	YitM of 194 aas and 2 or 3 TMSs in a 1 (N-terminal) + 1 or 2 TMS (C-terminal) arrangement. The B.subtilis yitPOM operon is a paralog of the sdpABC operon, which produces the secreted peptide toxin SDP. Unlike sdpABC, yitPOM is induced in biofilms by the DegS-DegU two-component regulatory system. High yitPOM expression leads to the production of a secreted toxin called YIT. Expression of yitQ, which lies upstream of yitPOM, confers resistance to the YIT toxin, suggesting that YitQ is an anti-toxin protein for the YIT toxin. The alternative sigma factor SigW also contributes to YIT toxin resistance. In a mutant lacking yitQ and sigW, the YIT toxin specifically inhibits biofilm formation, and the extracellular neutral protease NprB is required for this inhibition (Kobayashi and Ikemoto 2019).		YIT (YitM) of Bacillus subtilis

Examples:
TC#	Name	Organismal Type	Example
9.B.139.2.1	SdpC homologue	δ-Proteobacteria	SdpC of Myxococcus xanthus

Examples:
TC#	Name	Organismal Type	Example
9.B.139.3.1	SdpC homologue of 231 aas.	Actinobacteria	SdpC homologue of Corynebacterium diphtheriae

9.B.139.3.2	SdpC homologue	Actinobacteria	SdpC homolgue of Corynebacterium pseudogenitalium

Examples:
TC#	Name	Organismal Type	Example