Sporulation in Bacillus subtilis is independent of membrane fatty acid composition

Induction of L-form-like cell shape change of Bacillus subtilis under microculture conditions

A remarkable cell shape change was observed in Bacillus subtilis strain 168 under microculture conditions on CI agar medium (Spizizen's minimal medium supplemented with a trace amount of yeast extract and Casamino acids). Cells cultured under a cover glass changed in form from rod-shaped to spherical, large and irregular shapes that closely resembled L-form cells. The cell shape change was observed only with CI medium, not with Spizizen's minimum medium alone or other rich media. The whole-cell protein profile of cells grown under cover glass and cells grown on CI agar plates differed in several respects. Tandem mass analysis of nine gel bands which differed in protein expression between the two conditions showed that proteins related to nitrate respiration and fermentation were expressed in the shape-changed cells grown under cover glass. The cell shape change of CI cultures was repressed when excess KNO3 was added to the medium. Whole-cell protein analysis of the normal rod-shaped cells grown with 0.1% KNO3 and the shape-changed cells grown without KNO3 revealed that the expression of the branched-chain alpha-keto acid dehydrogenase complex (coded by the bfmB gene locus) was elevated in the shape-changed cells. Inactivation of the bfmB locus resulted in the repression of cell shape change, and cells in which bfmB expression was induced by IPTG did show changes in shape. Transmission electron microscopy of ultrathin sections demonstrated that the shape-changed cells had thin walls, and plasmolysis of cells fixed with a solution including 0.1 M sucrose was observed. Clarifying the mechanism of thinning of the cell wall may lead to the development of a new type of cell wall biosynthetic inhibitor.

cis-unsaturated fatty acids specifically inhibit a signal-transducing protein kinase required for initiation of sporulation in Bacillus subtilis

The initiation of sporulation in Bacillus subtilis is controlled by the Spo0A transcription factor which is activated by phosphorylation through a phosphorelay mechanism that is dependent upon the activity of one or more protein kinases. The enzymatic activity of one of these protein kinases, KinA, was found to be inhibited in vitro by certain fatty acids. The most potent inhibitors have at least one unsaturated double bond in the cis configuration and a chain length of 16-20 carbon atoms. Homologous isomers with a trans double bond are not inhibitory. Saturated straight- or branched-chain fatty acids are either much weaker inhibitors or have no effect. The inhibitors prevent autophosphorylation of KinA and are non-competitive with ATP. B. subtilis phospholipids were found to contain at least one as yet unidentified type of fatty acid that, when present in an unesterified form, inhibited KinA. The results suggest that the concentration of a specific unsaturated fatty acid may act as a signal linking the initiation of sporulation to the status of membrane synthesis and septation or some other specific membrane-associated activity.