Genetic characterization of ompH mutants in the deep-sea bacterium Photobacterium sp. strain SS9.

OmpH is an outer membrane protein produced by the deep-sea bacterium Photobacterium species strain SS9 in response to elevated hydrostatic pressure. In order to facilitate studies of the function of this protein, a series of OmpH+ and OmpH- strains were obtained from SS9 by Tn5 gene replacement mutagenesis. A previously isolated ompH::lacZ strain and a derivative of this strain harboring a plasmid expressing the wild-type ompH gene were also utilized. The acridine mutagen ICR 191 preferentially inhibited the growth of OmpH+ over OmpH- cells. Indeed, OmpH+ cultures treated with the mutagen rapidly accumulated mutants producing reduced levels of OmpH. In addition, OmpH+ cells took up the peptide Met-Leu-Phe approximately 15 times more rapidly than OmpH- cells. The results are consistent with the hypothesis that OmpH functions as a relatively large, nonspecific diffusion channel.