Repression of the activities of two extracytoplasmic function σ factors, σ^M and σ^V, of Bacillus subtilis by glucolipids in Escherichia coli cells

Extracytoplasmic function (ECF) σ factors respond to environmental stresses and regulate numerous genes required for adaptation. Under normal growth conditions, the ECF σ factors are sequestered by transmembrane anti-σ 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 σ factors, σ^M, σ^V and σ^X, are activated. The Escherichia coli cell membrane does not contain glucolipids. When the genes for these three ECF σ and anti-σ factors were introduced into E. coli cells, expression of lacZ fused to the ECF σ factor-regulated promoters indicated ECF σ 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 σ^M and σ^V were repressed, but the activity of σ^X was unaffected. It is likely that glucolipids directly influence anti-σ^M and anti-σ^V factors by stabilizing conformations that sequester the respective ECF σ factors.