Syringafactin production by Pseudomonas syringae, is contact-dependent and affects its local environment via its hygroscopicity
M. HERNANDEZ (1), S. Lindow (1) (1) University of California, Berkeley, U.S.A.

Pseudomonas syringae produces the biosurfactant syringafactin which has hygroscopic properties. The contribution of syringafactin to the water availability around cells was assessed in strains harboring a proU promoter fused with a gfp reporter gene. WT cells exhibited significantly less gfp fluorescence on humid but dry leaves than did a syringafactin-deficient strain indicating that syringafactin made water available to the cells. The viability of syringafactin-producing cells was more than 2-fold higher after prolonged incubation on dry leaves than that of syringafactin mutants as assessed using propidium iodide staining. The water absorbing potential of syringafactin is high (attraction of as much as 250% its weight in water) at high relative humidities (>93%) but is much less at lower relative humidities, suggesting that its benefit to the producing cells is strongly context dependent. Production of syringafactin is a strongly contact-dependent trait since syfA, encoding syringafactin production, is expressed at low levels in planktonic cells in liquid cultures but increases over 4-fold in cells contacting surfaces as varied as glass, plastics, paper, parafilm, leaves, agar, and membrane filters. Induction of syfA is rapid, occurring within 2 hours after attachment. Surfaces may be detected via inhibition of flagellar rotation since syfA  is induced in viscous culture containing 5% dextran.

Abstract Number: P3-71
Session Type: Poster