Temperature regulation and requirement of the nucleoid-structuring H-NS protein for the expression of ompW encoding the outer membrane colicin S4 receptor in Escherichia coli

LUCIANO BRAMBILLA; JORGELINA MORÁN BARRIO; ALEJANDRO VIALE

Rosario

Congreso; X Congreso Argentino de Microbiología.; 2013

UNR

OmpW is a small monomeric outer membrane (OM) β-barrel protein of not well defined function, ubiquitously distributed among Gram-negative bacteria. Variation of OmpW contents in different enterobacterial species in response to various environmental factors suggests roles in environmental adaptation, but the underlying mechanisms are unknown. Here, we report that Escherichia coli OmpW contents are regulated by temperature: While OmpW is present in cells grown at 28°C, it disappears from the OM when the growth temperature is reduced to 23°C. The use of ompW::lacZY fusions indicated that temperature regulation occurs mainly at the transcriptional level. The H-NS nucleoid structuring protein, a general silencer of gene expression and mediator of environmental cues, was the major protein recovered from E. coli crude extracts with a biotinylated ompW promoter probe. DNA mobility shift assays using purified H-NS further supported the presence of high affinity H-NS binding sites at the ompW promoter region, and uncovered the formation of higher order H-NS nucleoprotein structures at this region. Most remarkably, E. coli Dhns mutants lacking H-NS grown at either 23 or 28°C contained no detectable OmpW and showed basal levels of ompW::lacZY expression, thus indicating a specific demand of H-NS for ompW expression. Temperature regulation and H-NS requirement of ompW expression is suggested to play relevant roles in E. coli adaptation to radically changing environmental conditions.