Characterization of outer membrane proteins of Xenorhabdus nematophilus

The major outer membrane proteins of the primary and secondary phase variants of Xenorhabdus nematophilus produced during exponential and stationary phase growth were characterized. OpnP, the most highly expressed outer membrane protein of X. nematophilus, was purified as a monomer with a molecular weight of 30,000. The amino acid composition of OpnP was very similar to that of the porin proteins, OmpF and OmpC, of Escherichia coli, N-terminal amino acid sequence analysis revealed that residues 1-27 of the mature OpnP shared 60% sequence identity with OmpF. In vitro pore function analysis of purified OpnP indicated that the single channel conductance values were similar to that measured for OmpF. These results suggest that OpnP is the OmpF-like porin protein in X. nematophilus. Three additional proteins, OpnA, OpnB and OpnS were induced during stationary phase growth. We show that the stationary phase proteins, OpnA and OpnB, were not produced in secondary phase cells. OpnB was present at a high level in stationary phase cells grown at 19-30 degrees C, and was repressed in cells grown at 34 degrees C. OpnA was optimally produced at 30 degrees C and was not present in cells grown at lower and higher temperatures. The production of OpnS was not dependent on growth temperature. In contrast, another outer membrane protein, OpnT, was strongly induced as the growth temperature was elevated from 19 degrees to 34 degrees C.