Functional Identification of theProteusmirabilisCore Lipopolysaccharide Biosynthesis Genes

In this study, we report the identification of genes required for the biosynthesis of the core lipopolysaccharides (LPSs) of two strains ofProteus mirabilis . SinceP .mirabilis andKlebsiella pneumoniae share a core LPS carbohydrate backbone extending up to the second outer-core residue, the functions of the commonP .mirabilis genes was elucidated by genetic complementation studies using well-defined mutants ofK .pneumoniae . The functions of strain-specific outer-core genes were identified by using as surrogate acceptors LPSs from two well-definedK .pneumoniae core LPS mutants. This approach allowed the identification of two new heptosyltransferases (WamA and WamC), a galactosyltransferase (WamB), and anN -acetylglucosaminyltransferase (WamD). In both strains, most of these genes were found in the so-calledwaa gene cluster, although one common core biosynthetic gene (wabO ) was found outside this cluster.