ABSTRACT
In Escherichia coli, transcription of thedegP locus, which encodes a heat-shock-inducible periplasmic protease, is controlled by two parallel signal transduction systems that each monitor extracytoplasmic protein physiology. For example, the heat-shock-inducible sigma factor, ςE, controls degP transcription in response to the overproduction and folded state of various extracytoplasmic proteins. Similarly, the CpxA/R two-component signal transduction system increases degP transcription in response to the overproduction of a variety of extracytoplasmic proteins. SincedegP transcription is attuned to the physiology of extracytoplasmic proteins, we were interested in identifying negative transcriptional regulators of degP. To this end, we screened for null mutations that increased transcription from a strain containing a degP-lacZ reporter fusion. Through this approach, we identified null mutations in the wecE,rmlA
ECA, and wecF loci that increase degP transcription. Interestingly, each of these loci is responsible for synthesis of the enterobacterial common antigen (ECA), a glycolipid situated on the outer leaflet of the outer membrane of members of the family Enterobacteriaceae. However, these null mutations do not stimulate degP transcription by eliminating ECA biosynthesis. Rather, the wecE,rmlA
ECA, and wecF null mutations each impede the same step in ECA biosynthesis, and it is the accumulation of the ECA biosynthetic intermediate, lipid II, that causes the observed perturbations. For example, the lipid II-accumulating mutant strains each (i) confer upon E. colia sensitivity to bile salts, (ii) confer a sensitivity to the synthesis of the outer membrane protein LamB, and (iii) stimulate both the Cpx pathway and ςE activity. These phenotypes suggest that the accumulation of lipid II perturbs the structure of the bacterial outer membrane. Furthermore, these results underscore the notion that although the Cpx and ςE systems function in parallel to regulate degP transcription, they can be simultaneously activated by the same perturbation.
Mutations in enterobacterial common antigen biosynthesis restore outer membrane barrier function in
Escherichia coli tol‐pal
mutants
