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Results show that a recombinat cosmid carries the waa gene cluster mediating Klebsiella pneumoniae C3 core lipopolysaccharide biosynthesis as revealed by genetic complementation analyses of waa mutants.

The Serratia marcescens N28b wbbL gene complements the rfb-50 mutation of Escherichia coli K-12 derivatives and a wbbL mutant has been found to be damaged in O4-antigen biosynthesis. A recombinant cosmid containing the wbbL gene was examined by subcloning and determination of O-antigen production phenotype in E. coli DH5alpha. Findings revealed that a recombinant plasmid (pSUB6) containing approximately 10 kb of DNA insert is sufficient to induce O4-antigen biosynthesis.

The 282-residue WbbL protein is a rhammosyltransferase capable of complementing the rfb-50 mutation in Escherichia coli K-12 derivatives. The Serratia marcescens mutants were constructed through the mobilization of suicide plasmids containing a portion of rmlD or wbbL. The nucleotide sequence of the plasmid pJT101 insert was determined to identify the S. marcescens genes conferring serum resistance. However, the insertion mutants were not capable of producing O antigens.