Abstract 1345 Periplasmic glucans are required for envelope integrity and morphogenesis in Caulobacter

Maintaining a robust cell envelope under fluctuating environmental conditions is required for bacterial growth and survival. We recently discovered new players in the metabolism of osmoregulated periplasmic glucans (OPGs) in the alphaproteobacterium Caulobacter crescentus that are important for envelope integrity and antibiotic resistance. However, the mechanisms by which OPGs support envelope function and the functional importance of the OPG synthase OpgH were unknown. Using bacterial genetics, imaging, and biochemistry, we discovered that OpgH is essential for Caulobacter viability. Depletion of OpgH over time leads to profound morphogenetic defects and cell lysis. The morphology defects associated with OpgH depletion are in part attributable to mislocalization of key morphogenetic proteins including MipZ, FtsZ, and RodZ. Importantly, the enzymatic function of OpgH is required for viability as production of a catalytically dead mutant of OpgH phenocopies OpgH depletion. Interestingly, depletion of OpgH also phenocopies activation of the CenKR two-component system in Caulobacter. We propose that loss of OPGs disrupts periplasmic homeostasis in a manner that is sensed by CenK which then signals to modify cell physiology via the response regulator CenR. This work was funded in part by the National Institute of General Medical Sciences under grants R35GM136221 (to EDG) and T32Gm144272 (training grant support of AKD and ES).