Structurally diverse natural products that cause potassium leakage trigger multicellularity in Bacillus subtilis

Abstract

We report a previously undescribed quorum-sensing mechanism for triggering multicellularity in Bacillus subtilis. B. subtilis forms communities of cells known as biofilms in response to an unknown signal. We discovered that biofilm formation is stimulated by a variety of small molecules produced by bacteria-including the B. subtilis nonribosomal peptide surfactin-that share the ability to induce potassium leakage. Natural products that do not cause potassium leakage failed to induce multicellularity. Small-molecule-induced multicellularity was prevented by the addition of potassium, but not sodium or lithium. Evidence is presented that potassium leakage stimulates the activity of a membrane protein kinase, KinC, which governs the expression of genes involved in biofilm formation. We propose that KinC responds to lowered intracellular potassium concentration and that this is a quorum-sensing mechanism that enables B. subtilis to respond to related and unrelated bacteria.biofilm ͉ quorum sensing

Connection of KinC to flotillins and potassium leakage in Bacillus subtilis

“…The kinC mutant phenotype (Fig. 2a, b) appears strikingly different to what has been published by several groups (Ló pez et al, 2009a;McLoon et al, 2011). Furthermore, we have never detected early sporulation in a kinC mutant.…”

“…Devi et al (2015) explain in their Introduction that a surfactin-deficient strain activates KinC when grown in DSM medium. The authors stated that this is contradictory to the published model, in which surfactin activates KinC in MSgg medium (Ló pez et al, 2009a). However, these two different observations should not be considered as contradictory.…”

“…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 (Ló pez et al, 2009a(Ló pez et al, , b, 2010. To sense surfactin, KinC is required to localize in the functional membrane microdomains .…”

In vivo functional characterization of the transmembrane histidine kinase KinC in Bacillus subtilis

“…More recently, using the undomesticated B. subtilis strain NCIB 3610, KinC has been demonstrated to contribute to triggering biofilm formation (Ló pez et al, 2009a). In the proposed model, the lipopeptide antibiotic surfactin is secreted into the medium by some cells in culture, thereby inducing membrane leakage of other cells in the population, leading to lowering the intracellular potassium concentration.…”

Phosphorylation of Spo0A by the Histidine Kinase KinD Requires the Lipoprotein Med in Bacillus subtilis

“…It is thought that the activity of the kinases is regulated by specific signals whose nature is largely mysterious. KinA and KinB are particularly important for entry into sporulation (29,37), whereas KinC and KinD contribute to triggering biofilm formation (23). Three of the kinases are integral membrane proteins (KinB, KinC, and KinD), whereas the fourth, KinA, is cytosolic.…”