B-181. Identification and Characterization of QseD a Putative LysR Like Regulator of Virulence, Motility, and Genome and Cellular Stability in Enterohemorrhagic E. coli

B. J. Habdas;
Univ. of Texas Southwestern Med. Center, Dallas, TX.

Enterohemorrhagic E. coli O157:H7 (EHEC) is the major causative agent of hemorrhagic colitis and hemolytic uremic syndrome throughout the world. EHEC encodes for the production of two functional type III secretion systems (TTSS). One of these systems encodes for flagella production. The other system, encoded by the locus of enterocyte effacement (LEE), allows for the formation of attaching and effacing (AE) lesions. Both TTSS are regulated by quorum sensing through two-component systems and LysR regulators. This regulation may allow for phenotypic switching between luminal swimming motility and intimate AE lesion attachment. We have discovered a LysR regulator, renamed QseD, which lacks the DNA binding motif, and could be responsible for this phenotypic switching event. QseD exists in all sequenced EHEC O157:H7 isolates as the truncated form; however, a full length functional LysR is present in other E. coli strains. The LysR family of transcriptional regulators binds DNA as hetero and homo-oligomers. Thus, QseD, through interactions with endogenous LysRs could be a EHEC genetic switch, as the genome contains both a negative LysR regulator of motility, LrhA, and a positive LysR regulator of LEE expression, QseA. To understand QseD’s regulatory role, an isogenic mutant was constructed and complemented by either truncated EHEC qseD or full length K-12 E. coli qseD. The qseD mutant in EHEC displayed reduced motility and deregulated transcription of the flagella genes, while exhibiting increased expression of all LEE operons. Complementation with the truncated QseD restored gene expression to previous levels, whereas complementation with the full length QseD resulted in an opposite expression profile. QseD additionally regulates multiple pathways involved in genome and cellular stability, such as DNA repair, and the production of heat shock proteins, metabolic enzymes, recombinases, integrases, and several other phage regulatory and structural proteins. We propose that QseD, a truncated, LysR-like transcriptional regulator, relieves DNA binding by endogenous LysR family members by forming hetero-oligomers with them thus altering global gene expression profiles and lineage stability.