SwrAA activates poly-gamma-glutamate synthesis inaddition to swarming in Bacillus subtilis

Poly-gamma-glutamic acid (γ-PGA) is an extracellular polymer produced by various strains of Bacillus. Ιt was first described as the component of the capsule in B. anthracis, where it plays a relevant role in virulence. γ-PGA is also a distinctive component of “natto”, a Japanese traditional food consisting of soybean fermented by B. subtilis (natto). Domesticated B. subtilis strains do not synthesize γ-PGA although they possess the functional biosynthetic pgs operon. In the present work we explore the correlation between the genetic determinants, swrAA and degU, which allow a derivative of the domestic strain JH642 to display a mucoid colony morphology on LB agar plates due to the production of γ-PGA. Full activation of the pgs operon requires the co-presence of SwrAA and the phosphorylated form of DegU (DegU~P). The presence of either DegU~P or SwrAA alone has only marginal effects on pgs operon transcription and γ-PGA production. Although SwrAA was identified as necessary for swarming and full swimming motility together with DegU, we show that motility is not involved in γ-PGA production. Activation of γ-PGA synthesis is therefore a motility-independent phenotype in which SwrAA and DegU~P display a cooperative effect.