Genomic and Proteomic Studies on Plesiomonas shigelloides

We report here the identification ofwaa clusters with the genes required for the biosynthesis of the core lipopolysaccharides (LPS) of two Plesiomonas shigelloides strains. Both P. shigelloides waa clusters shared all of the genes besides the ones flanking waaL. In both strains, all of the genes were found in thewaa gene cluster, although one common core biosynthetic gene (wapG) was found in a different chromosome location outside the cluster. Since P. shigelloides and Klebsiella pneumoniae share a core LPS carbohydrate backbone extending up at least to the second outer-core residue, the functions of the common P. shigelloides genes were elucidated by genetic complementation studies using well-defined K. pneumoniaemutants. The function of strain-specific inner- or outer-core genes was identified by using as a surrogate acceptor LPS from three well-defined K. pneumoniae core LPS mutants. Using this strategy, we were able to assign a proteomic function to all of the P. shigelloides waa genes identi-fied in the two strains encoding six new glycosyltransferases (WapA,-B,-C,-D,-F, and-G). P. shigelloides demonstrated an im-portant variety of core LPS structures, despite being a single species of the genus, as well as high homologous recombination in housekeeping genes. Plesiomonas shigelloides is a species of rod-shaped Gram-nega-tive bacteria recently classified in the family Enterobacteriaceae and is the only oxidase-positive member of this family (1). Fresh-water and estuarine water are considered to be the natural envi-ronment of P. shigelloides, which is often isolated from fish an