PHYSICAL LINKAGE OF THE VIBRIO-CHOLERAE MANNOSE-SENSITIVE HEMAGGLUTININ SECRETORY AND STRUCTURAL SUBUNIT GENE LOCI - IDENTIFICATION OF THE MSHG CODING SEQUENCE

Vibrio cholerae O1 expresses a variety of cell surface factors which m ediate bacterial adherence and colonization at the intestinal epitheli um. The mannose-sensitive hemagglutinin (MSHA), a type IV pilus, is a potential attachment factor of the V. cholerae El Tor biotype. We desc ribe a TnphoA mutant that is defective in its ability to hemagglutinat e mouse erythrocytes. The TnphoA insertion maps to a recently identifi ed genetic locus that encodes products that are predicted to be essent ial for assembly and export of the MSHA pilus. Insertional disruption at this locus in a mshA-phoA reporter strain provides evidence for a r ole of this locus in the latter stages of pilus assembly and/or export . These constructs have provided physical markers by which we have est ablished close physical linkage of this secretion locus to a set of ge nes that includes the mshA structural gene. Sequence analysis of the i ntervening region between these two loci has revealed the presence of an open reading frame with homology to pilus biogenesis genes of sever al gram-negative bacteria. This genetic organization suggests an entir e operon encoding the MSHA pilus and the components necessary for its assembly and secretion to the bacterial cell surface. The nomenclature of the MSHA structural and secretory locus has been redefined accordi ngly.