Regulation of the Uropathogenic Escherichia coli tos Operon and Its Implications for an Expansion of Microbial Reciprocal Regulation Between Adherence- and Motility-Related Genes.

Abstract

Urinary tract infections (UTIs) are among the most common bacterial infections and are commonly caused by uropathogenic Escherichia coli (UPEC). UPEC do not have a fixed set of virulence and fitness factors. Instead, UPEC strains use a variety of these factors to establish infection. There are also a number of genetic networks connecting UPEC virulence and fitness genes. One network is the reciprocal regulation network connecting E. coli motility- and adhesin-encoding genes. For instance, when adhesin genes are expressed, motility genes are repressed, and when motility genes are expressed, adhesin genes are repressed. UPEC strain CFT073 also harbors the tos operon, which encodes the regulatory, secretion, and adherence machinery of a repeats-in-toxin (RTX) nonfimbrial adhesin, TosA (for type one secretion protein A). This adhesin promotes UPEC adherence to host cells derived from the upper urinary tract and is expressed primarily in vivo. Little else was known about tos operon expression. I hypothesized that regulators encoded in the tos operon, regulators encoded elsewhere in the E. coli genome, and environmental conditions encountered in the urinary tract mediate tos operon expression. It is also my hypothesis that reciprocal regulation of adhesin- and motility-related genes is part of tos operon regulation, and regulators encoded in the tos operon are part of this network. Using a variety of in vitro approaches, I identified that TosR, a member of the PapB family, is a tos operon dual positive and negative regulator. In addition, the tos operon promoter, Ptos, is upstream of tosR, and there are at least two TosR binding sites in the vicinity of Ptos. Nucleoid-associated proteins H-NS and Lrp, both associated with adherence and motility reciprocal regulation, function in negative and positive regulation of the tos operon, respectively. Leucine inhibits tos operon expression. Therefore, the tos operon is responsive to conditions encountered in vivo (low leucine). TosEF, encoded by the tos operon, suppress motility by inhibiting FliC production, and TosR perturbs adhesin regulation. Thus, tos operon regulation is related to the reciprocal regulation network. My work explains tos operon regulation and expands the knowledge of adhesin- and motility-encoding gene reciprocal regulation.