PREVALENCE OF GCA, A GENE INVOLVED IN SYNTHESIS OF A-BAND COMMON ANTIGEN POLYSACCHARIDE IN PSEUDOMONAS-AERUGINOSA

Two distinct forms of lipopolysaccharide are expressed by Pseudomonas aeruginosa. These forms are known as the A band and the B band, In an attempt to obtain a better understanding of ii-band lipopolysaccharide synthesis, a previously isolated A-band gene known as the gca gene (G DP-D-mannose conversion protein for A-band common antigen polysacchari de) was sequenced and analyzed, Previous protein expression data from our laboratory, along with nucleotide sequence analysis from the prese nt study, suggest that the Gca protein is encoded by the open reading frame ORF36.5. Amino acid homology reveals that this protein may be fu nctioning as a dehydratase or as a bifunctional enzyme, facilitating t he conversion of GDP-D-mannose to GDP-D-rhamnose, The distribution of this gca gene among the 20 P. aeruginosa O serotypes, clinical isolate s, and other Pseudomonas species was also examined. Southern hybridiza tion results revealed that the gca gene is present and conserved on a 1,6-kb KpnI fragment among all 20 O serotypes with the exception of se rotype O12. In addition, the gca gene is not universally found among a ll pseudomonads; however, probe-reactive profiles are similar to that of P, aeruginosa when the gca gene is present. Primers were designed f rom the Sea nucleotide sequence, and PCR amplification of a 700-bp pro duct was found,with each of the 20 O serotypes. Because of the conserv ation of this gene, gca may be useful as a diagnostic tool for detecti ng the presence of P. aeruginosa as well as other Pseudomonas species.