Responses of Escherichia coli to the neutrophil bactericidal/permeability-increasing protein

The Bactericidal/permeability-increasing protein (BPI) is an endotoxin-binding protein that promotes host defense against invading gram-negative bacteria. Binding of BPI to outer membrane (OM) lipopoysaccharides (LPS, endotoxin) rapidly induces sublethal alterations that can lead to bacterial death. The preservation of bacterial metabolic activity during the initial sublethal attack by BPI suggests that E. coli could adaptively respond to sublethal attack by BPI and thereby increase the probability of bacterial survival. The goal of this thesis was to identify molecular mechanisms that mediate such adaptive responses.; We have identified the global regulator OmpR as a mediator of a subset of acute bacterial responses to BPI. Within 15 minutes, BPI induces reciprocal changes in the synthesis of two major OM porins, OmpF and OmpC, that depend on phosphorylation of OmpR. Bacteria that lack OmpR are less tolerant to BPI-mediated sublethal damage but not because of changes in ompF and ompC expression. By transcriptome analysis, we have found that nearly 18% of all bacterial genes are regulated by OmpR and that over 30% of all BPI-induced mRNA changes are OmpR-dependent. This suggests that additional OmpR-regulated gene products could be important in bacterial resistance to killing by BPI.; Changes in OmpR function induced by BPI are mediated via the hybrid anaerosensor ArcB and by acetyl-phosphate but not via the cognate sensor EnvZ. Signaling through ArcB not only affects OmpR but also activates the response regulator ArcA.{09}Activation of ArcA-dependent responses suggests that BPI-treated bacteria can switch from aerobic to anaerobic fermentative metabolism, in part by downregulating expression of enzymes mediating oxidative phosphorylation and the tricarboxylic acid cycle. At the same time, many genes encoding efflux pumps and other protective responses are upregulated possibly secondary to sublethal changes in OM permeability and respiratory metabolism. Remarkably, nearly 60% of transcripts upregulated by BPI correspond to genes of unknown function.; In summary, sublethal alterations produced by BPI induce multiple signals which the bacteria use to respond to initial BPI attack. When amounts of BPI present are limiting, such adaptive changes could promote repair of bacterial injury and promote survival.