Comparative analyses of Serratia spp. outer membrane porin proteins

Eight Serratia strains and several members of the Enterobacteriaceae family were used in immunoblot and Southern DNA hybridization experiments and probed with antibody and DNA probes specific for the 41-kDa Serratia marcescens porin, to determine the extent of homology between Gram-negative porins. Immunoblot analyses performed using porin-specific rabbit sera and cell envelope preparations from these strains revealed that all strains produced at least one cross-reactive protein in the 41-kDa molecular weight range. Chromosomal DNA from each of the same strains was used in Southern analyses, probed with a 20-base-length oligonucleotide probe deduced from the N-terminal amino acid sequence of the 41-kDa Serratia marcescens porin. The probe hybridized to DNA from all of the Serratia species and six of the nine other enteric bacteria. Putative porin proteins from all the Serratia species were subjected to N-terminal amino acid sequencing and porin functional analysis using the black lipid bilayer method. All amino acid sequences were identical, with one exception in which an asparagine was substituted for an aspartic acid in Serratia rubidaea. All porins had very similar porin function (single channel conductance ranging between 1.72 and 2.00 nS). The results from this study revealed that a strong conservation exists among the Serratia porins and those produced by other enteric bacteria.