AND R . KUSUDA. 1996. Lastonella (Vibrio) anguillarum, an important fish pathogen, is divided into 10 serotypes according to O-antigens present on the outer membrane. However, the biochemical and immunological properties of porin proteins have not been reported. In this study, the antigenicity and N-terminal amino acid sequence of the 35 kDa porin-like-major outer membrane protein (Omp35La) were compared among different serotypes of L. anguillarum as well as other bacteria. In Western blotting analysis, antisera against Omp35La from strains of J-0-1, -2 and -3 serotypes could detect Omp35La, but not other proteins, in most L. anguillarum strains and isolates of the genera Vibrio and Photobacterium. This antigenicity of Omp35La is unrelated to the serotype and is conserved in related organisms. An N-terminal sequence showed identification with OmpF and OmpC of Escherichia coli and Salmonella typhimurium. However, this similarity was lower when compared to other human pathogens. Thus it was concluded that Omp35La does not contribute to the serotypes of L. anguillarum, although the N-terminal structure is well conserved among different serotypes.

Outer membrane proteins (OMP) of the marine fish pathogen, Vibrio (Listonella) anguillarum, were examined in a wild type strain and an oxytetracycline (OTC) resistant strain. When the OTC resistant strain was cultured in the presence of OTC, the concentration of a major porin, Omp35La, decreased whereas the concentration of an unknown 26kDa OMP increased. The latter OMP was designated Omp26La. The change in the expression of Omp35La and Omp26La was unaffected by treatment with tetracycline, chlorotetracycline, maltose, rafinose and glucose. Additionally, heat shock treatment did not affect the OMP profiles. Although whether the regulation of both OMPs correlates or not is unclear, it is suggested that OTC specifically affected the expression of both OMPs in the OTC resistant strain. The nucleotide and deduced amino acid sequences of Omp26La were similar to the known OMP (OmpV) of Vibrio cholarae. From the amino acid composition and hydropathy profile, Omp26La was found to have a similar structure to porins such as OmpC and OmpF of E. coll.