Nitric oxide inhibits biofilm formation by Vibrio fischeri via the nitric oxide sensor HnoX

Biofilm formation byVibrio fischeri is positively controlled by the sensor kinase HahK, which activates transcription of thesyp locus, resulting in the production of the major polysaccharide component of the matrix and permitting cell aggregation phenotypes. HahK is negatively regulated by the nitric oxide ‐binding protein HnoX. Thus, presence of nitric oxide controls biofilm formation by negatively controlling the activities of HnoX and thus HahK, ultimately impactingsyp transcription and production of matrix polysaccharide. SummaryNitric oxide (NO) is an important defense molecule secreted by the squidEuprymna scolopes and sensed by the bacterial symbiont,Vibrio fischeri, via the NO sensor HnoX. HnoX inhibits colonization through an unknown mechanism. The genomic location ofhnoX adjacent tohahK, a recently identified positive regulator of biofilm formation, suggested that HnoX may inhibit colonization by controlling biofilm formation, a key early step in colonization. Indeed, the deletion ofhnoX resulted in early biofilm formationin vitro, an effect that was dependent on HahK and its putative phosphotransfer residues. An allele ofhnoX that encodes a protein with increased activity severely delayed wrinkled colony formation. Control occurred at the level of transcription of thesyp genes, which produce the polysaccharide matrix component. The addition of NO abrogated biofilm formation and diminishedsyp transcription, effects that required HnoX. Finally, anhnoX mutant formed...

Source: Molecular Microbiology - November 11, 2018 Category: Microbiology Authors: Cecilia M. Thompson, Alice H. Tischler, Denise A. Tarnowski, Mark J. Mandel, Karen L. Visick Tags: Research Article Source Type: research