Global Regulatory Control of Curli Expression and Fibronectin Binding in Enterobacteria

Abstract

Many bacterial virulence-associated properties are affected by changes in the environment. For example, changes in growth temperature, osmolarity or oxygen tension may increase or decrease expression of adhesive organelles. Expression of Vibrio cholerae Tcp pili depends specifically on a transmembrane signal transmitter protein, ToxR (Miller et al., 1987). Expression of other types of pili appears to be subjected to a more global regulatory control that may involve DNA topology. Escherichia coli Pap pili expression is thermoregulated such that these adhesive structures are formed at 37°C but not at room temperature (Goransson and Uhlin, 1984). This low temperature repression operates at the level of transcription and can be relieved by a drdX mutation in the structural gene for the histone-like protein, H1 (Goransson et al., 1990). Mutations in this gene have been isolated in many laboratories using different screening or selection protocols (Higgins et al., 1990), and the H1 gene has been given many designations, including bglY, drdX, hns, pilG, osmZ, and virR. Mutations in H1 affect gene expression of osmoregulated genes such as proU, hence the name osmZ for the locus (Higgins et al., 1988). The E. coli K12 bgl operon for β-glucoside metabolism is normally cryptic, but can be activated by bglY mutations (Defez and DeFelice, 1981).