Figure 8. Model for the role of colicins for bacterial competition in inflammation-induced blooms.

(A) Under homeostatic conditions, Enterobacteriaceae (blue, green) are reduced in numbers as they are kept in check by the obligate anaerobic microbiota (violet-blue). Under this condition, colicin expression as well as expression of the colicin surface receptors are relatively repressed (high iron, no triggers of the SOS response). (B) Upon induction of an inflammatory response, gut microbial ecology is altered leading to Enterobacterial blooms. Neutrophils transmigrate into the gut lumen and produce iron-depleting agents (lipocalin, lactoferrin) and reactive oxygen and nitrogen species (ROS, RNS). This triggers SOS-and Fur-dependent transcriptional responses in Enterobacteriaceae and colicin- and colicin-receptor expression is induced. Thereby, the inflammatory response drives colicin-dependent enterobacterial competition.