Repression of the activities of two extracytoplasmic function σ factors, σM and σV, of Bacillus subtilis by glucolipids in Escherichia coli cells

Extracytoplasmic function (ECF) sigma factors respond to environmental stresses and regulate numerous genes required for adaptation. Under normal growth conditions, the ECF sigma factors are sequestered by transmembrane anti-sigma factor proteins, from which they are released under stress conditions. In Bacillus subtilis ugtP null mutant cells, which lack glucolipids, three of the seven ECF sigma factors, sigma(M), sigma(V) and sigma(X), are activated. The Escherichia coli cell membrane does not contain glucolipids. When the genes for these three ECF sigma and anti-sigma factors were introduced into E. coli cells, expression of lacZ fused to the ECF sigma factor-regulated promoters indicated ECF sigma factor activity. Additional expression of the ugtP gene in these E. coli cells led to the synthesis of small amounts of glucolipids, and the activities of sigma(M) and sigma(V) were repressed, but the activity of sigma(X) was unaffected. It is likely that glucolipids directly influence anti-sigma(M) and anti-sigma(V) factors by stabilizing conformations that sequester the respective ECF sigma factors.