ALGINATE SYNTHESIS IN PSEUDOMONAS-AERUGINOSA - THE ROLE OF ALGL (ALGINATE LYASE) AND ALGX

Previous studies localized an alginate lyase gene (alaL) within the al ginate biosynthetic gene cluster at 34 min on the Pseudomonas aerugino sa chromosome. Insertion of a Tn501 polar transposon in a gene (algX) directly upstream of alaL in mucoid P. aeruginosa FRD1 inactivated exp ression of algX, algL, and other downstream genes, including algA. Thi s strain is phenotypically nonmucoid; however, alginate production cou ld be restored by complementation in trans with a plasmid carrying all of the genes inactivated by the insertion, including algL and algX. A lginate production was also recovered when a merodiploid that generate d a complete alginate gene cluster on the chromosome was constructed. However, alginate production by merodiploids formed in the algX::Tn501 mutant using an alginate cluster with an algL deletion was not restor ed to wild-type levels unless algL, was provided on a plasmid in trans . In addition, complementation studies of Tn501 mutants using plasmids containing specific deletions in either algL, or algX revealed that b oth genes were required to restore the mucoid phenotype. Escherichia c oli strains which expressed algX produced a unique protein of similar to 53 kDa, consistent with the gene product predicted from the DNA seq uencing data. These studies demonstrate that AlgX, whose biochemical f unction remains to be defined, and AlgL, which has alginate lyase acti vity, are both involved in alginate production by P. aeruginosa.