Ssg, a putative glycosyltransferase, functions in lipo- and exopolysaccharide biosynthesis and cell surface-related properties in Pseudomonas alkylphenolia

In the presence of vaporized p-cresol, Pseudomonas alkylphenolia KL28 forms specialized aerial structures (SAS). A transposon mutant of strain KL28 (C23) incapable of forming mature SAS was isolated. Genetic analysis of the C23 mutant revealed the transposon insertion in a gene (ssg) encoding a putative glycosyltransferase, which is homologous to the Pseudomonas aeruginosa PAO1 PA5001 gene. Deletion of ssg in KL28 caused the loss of lipopolysaccharide O antigen and altered the composition of the exopolysaccharide. Wild-type KL28 produced a fucose-, glucose- and mannose-rich exopolysaccharide, while the mutant exopolysaccharide completely lacked fucose and mannose, resulting in an exopolysaccharide with glucose as the major component. The mutant strain showed reduced surface spreading, pellicle and biofilm formation, probably due to the cumulative effect of lipopolysaccharide truncation and altered exopolysaccharide composition. Our results show that the ssg gene of KL28 is involved in both lipopolysaccharide and exopolysaccharide biosynthesis and thus plays an important role in cell surface properties and cell-cell interactions of P. alkylphenolia.