Isolation and Characterization of the algD gene of Pseudomonas syringae pv. phaseolicola and its distribution among other Pseudomonads and related Organisms

The gene coding for GDP-mannose dehydrogenase (algD) was isolated from a Pseudomonas syringae pv. phaseolicola genomic library using a polymerase chain reaction-generated heterologous DNA-probe from Pseudomonas aeruginosa. A total of 2123 base pairs were sequenced (accession number AF001555) and analysed for homologies to the alginate gene cluster of P. aeruginosa. Downstream from algD an alg8 homo- logue was found suggesting a similar arrangement of the alginate gene cluster in P. syringae pv. phaseolicola to that in P. aeruginosa. Also, the deduced amino acid sequence of algD shows high similarity to that of P. aeruginosa (0.9) and Azotobacter vinelandii (0.88). Southern hybridization experiments revealed that algD is widely distributed among members of the Pseudomonas rRNA homology group I. Among others, sequences homologous to algD were detected in the P. syringae pathovars lachrymans, mori, morsprunorum, pisi, savas- tanoi, tabaci and tomato as well as in Pseudomonas amygdali. For most of the algD positive organisms synthesis of alginate has been reported by other studies. However, algD homologues were also detected for the species Pseudomonas corrugata, Pseudomonas marginalis and Pseudomonas avenae (Acidovorax avenae), for which alginate biosynthesis has not yet been reported