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 A-band lipopolysaccharide synthesis, a previously isolated A-band gene known as the gca gene (GDP-D-mannose conversion protein for A-band common antigen polysaccharide) was sequenced and analyzed. Previous protein expression data from our laboratory, along with nucleotide sequence analysis from the present study, suggest that the Gca protein is encoded by the open reading frame ORF36.5. Amino acid homology reveals that this protein may be functioning as a dehydratase or as a bifunctional enzyme, facilitating the conversion of GDP-D-mannose to GDP-D-rhamnose. The distribution of this gca gene among the 20 P. aeruginosa O serotypes, clinical isolates, and other Pseudomonas species was also examined. Southern hybridization 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 serotype O12. In addition, the gca gene is not universally found among all pseudomonads; however, probe-reactive profiles are similar to that of P. aeruginosa when the gca gene is present. Primers were designed from the gca nucleotide sequence, and PCR amplification of a 700-bp product was found with each of the 20 O serotypes. Because of the conservation of this gene, gca may be useful as a diagnostic tool for detecting the presence of P. aeruginosa as well as other Pseudomonas species.