OPAR, A HOMOLOG OF VIBRIO-HARVEYI LUXR, CONTROLS OPACITY OF VIBRIO-PARAHAEMOLYTICUS

Vibrio parahaemolyticus is an organism weal adapted to communal life o n surfaces. When gown on a surface or in a viscous layer, the bacteriu m induces a large gene system and differentiates to swarmer cells capa ble of movement over and colonization of surfaces, V. parahaemolyticus displays additional phenotypic versatility manifested as variable col ony morphology, switching between translucent and opaque colony types. Although not itself luminescent, V. parahaemolyticus produces autoind ucer molecules capable of inducing luminescence in Vibrio harveyi. TO examine the sole of quorum signaling ire the lifestyles of V. parahaem olyticus, the functional homolog of the gene encoding the V. harveyi a utoinducer-controlled transcriptional regulatory protein LuxR was clon ed. Sequence analysis of the clone predicted ran open reading frame wi th a deduced product 96% identical to LuxR, introduction of the clone carrying the luxR-like locus into V. parahaemolyticus dramatically aff ected colony morphology, converting a translucent strain to an opaque one. When the coding sequence for the luxR homolog was placed under th e control of the Ptac promoter, conversion to the opaque phenotype bec ame inducible by isopropyl-beta-D-thiogalactopyranoside. Allelic disru ption of the luxR-like gene ore the chromosome of an opaque strain pro duced a translucent strain proficient in swarming ability, Primer exte nsion mapping demonstrated opaR transcription in opaque but not transl ucent cell types, It is postulated that this gene, which has been name d opaR, encodes a transcription factor controlling cell type. The unde rlying genetic basis for opaque-translucent variation may be the conse quence of a genomic alteration detected in the opaR locus of opaque an d translucent strains.