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.