Identification of Bacillus subtilis SipW as a bifunctional signal peptidase that controls surfaceadhered biofilm formation

D ow nloaded from 2 ABSTRACT 21 Biofilms of microbial cells encased in an exopolymeric matrix can form on solid-surfaces, but 22 how bacteria sense a solid surface and up-regulate biofilm genes is largely unknown. We 23 investigated the role of the Bacillus subtilis signal peptidase, SipW, which has a unique role in 24 forming biofilms on a solid surface and that is not required at an air-liquid interface. Surprisingly, 25 we found that the signal peptidase activity of SipW was not required for solid-surface biofilms. 26 Furthermore, a SipW mutant protein was constructed that lacks the ability to form a solid-surface 27 biofilm, but still retains signal peptidase activity. Through genetic and gene expression tests, the 28 non-signal peptidase role of SipW was found to activate biofilm matrix genes specifically when 29 cells were on a solid surface. These data provide the first evidence that a signal peptidase is 30 bifunctional and that SipW has a regulatory role in addition to its role as a signal peptidase. 3