Regulators H-NS and LeuO inversely control swarming motility and biofilm formation inVibrio parahaemolyticus

Abstract

Vibrio parahaemolyticusis a halophile present in marine environments worldwide and is a leading cause of bacterial seafood-borne gastroenteritis. Free livingVibrio parahaemolyticusplanktonic cells can either attach to surfaces to form swarming cells or develop into a sessile three-dimensional biofilm structure. Swarming motility requires lateral flagella (lafoperon) and the expression of the surface sensing operonscrABCto produce a spreading cauliflower colony morphology. Biofilms are formed from capsule polysaccharide (CPS) encoded by thecpsA-Koperon that is positively regulated by CpsR and CpsQ. In enteric bacteria, H-NS is a global gene silencer and LeuO is an antagonist of H-NS. In this work, we examined the role of these regulators in the decision between swarming and biofilm behaviors using deletion mutants ofleuO, hns,and a double deletionleuO/hns. The wild type and ΔleuOstrains produced swarming colonies whereas Δhnsproduced a hyper swarming whereas in ΔleuO/Δhns,the phenotype reverted to wild type. Transcriptional reporter assays of PlafB-gfpand PscrA-gfpshowed significantly increased fluorescence in Δhnscompared to wild type. In the ΔleuO/Δhnsmutant, PlafB-gfpfluorescence reverted to wild type levels and PscrA-gfpshowed increased fluorescence compared to wild type. In CPS assays, ΔleuOhad a less dense rugose morphology compared to wild type and Δhnsproduced a smooth colony, which also produced significantly less biofilm. ΔleuO/Δhnshad an opaque morphology and produced significantly more biofilm. Reporter expression assays of PcpsA-gfpand PcpsR-gfpconfirmed the roles of both H-NS and LeuO in CPS and biofilm formation.ImportanceThis study determined the role of LeuO and H-NS in controlling the decision between two surface based behaviors, swarming motility and sessile biofilm formation inV. parahaemolyticus. The effects of deletions ofleuO,hns,and a double ΔleuO/Δhnsmutant showed that H-NS was a negative regulator of swarming, but a positive regulator of biofilm formation. The mechanism of this control was in part due to H-NS inhibition of LeuO at loci required for swarming and biofilm formation.