Connection of KinC to flotillins and potassium leakage in Bacillus subtilis

Five different kinases (KinA-E) activate the regulator Spo0A to induce sporulation and biofilm formation in Bacillus subtilis (Jiang et al., 2000; LeDeaux et al., 1995). The signals that activate these kinases are currently unknown although, it was recently discovered that KinC senses membrane damage that involves the release of cytoplasmic potassium, which is caused by several small molecules, including the antimicrobial surfactin (Lopez et al., 2009a; Lopez et al., 2009b; Lopez et al., 2010). To sense surfactin, KinC is required to localize in the Functional Membrane Microdomains (FMMs) (Lopez & Kolter, 2010). These membrane regions contain two scaffold proteins named flotillins (FloT and FloA) that may facilitate interaction of FMM-associated proteins. Consequently, a flotillin-deficient strain shows reduced activity of KinC and other FMM-associated proteins, which leads to a decreased capacity to form a biofilm via activation of KinC (Lopez & Kolter, 2010; Yepes et al., 2012). A recent publication from the laboratory of Prof. Masaya Fujita (University of Houston, USA) (Devi et al., 2015) shows that the tetrameric form of KinC is required to activate biofilm formation. The authors note that some of their results are contradictory to previously published work from other research groups, including ours. The following paragraphs delineate some important issues of this report that prohibit any direct comparison to previously published work and provide a means to put the previous work on KinC in the correct context.