A novel two-component regulatory system in Bacillus subtilis for the survival of severe secretion stress

The Gram-positive eubacterium Bacillus subtilis is well known for its high capacity to secrete proteins into the environment. Even though high-level s ecretion of proteins is an efficient process, it imposes stress on the cell . The present studies were aimed at the identification of systems required to combat this so-called secretion stress. A two-component regulatory syste m, named CssR-CssS was identified, which bears resemblance to the CpxR-CpxA system of Escherichia coli. The results show that the CssR/S system is req uired for the cell to survive the severe secretion stress caused by a combi nation of high-level production of the alpha -amylase AmyQ and reduced leve ls of the extracytoplasmic folding factor PrsA. As shown with a prsA3 mutat ion, the Css system is required to degrade misfolded exported proteins at t he membrane-cell wall interface. This view is supported by the observation that transcription of the htrA gene encoding a predicted membrane-bound pro tease of B. subtilis, is strictly controlled by CssS. Notably, CssS represe nts the first identified sensor for extracytoplasmic protein misfolding in a Gram-positive eubacterium. In conclusion, the results show that quality c ontrol systems for extracytoplasmic protein folding are not exclusively pre sent in the periplasm of Gram-negative eubacteria, but also in the Gram-pos itive cell envelope.