Involvement of the exopolysaccharide alginate in the virulence and epiphytic fitness of Pseudomonas syringae pv. syringae

Abstract

SummaryAlginate, a co-polymer of O-acetylated b-1,4-linked D-mannuronic acid and L-guluronic acid, has been reported to function in the virulence of Pseudomonas syringae, although genetic studies to test this hypothesis have not been undertaken previously. In the present study, we used a genetic approach to evaluate the role of alginate in the pathogenicity of P. syringae pv. syringae 3525, which causes bacterial brown spot on beans. Alginate biosynthesis in strain 3525 was disrupted by recombining Tn5 into algL, which encodes alginate lyase, resulting in 3525.L. Alginate production in 3525.L was restored by the introduction of pSK2 or pAD4033, which contain the alginate biosynthetic gene cluster from P. syringae pv. syringae FF5 or the algA gene from P. aeruginosa respectively. The role of alginate in the epiphytic ®tness of strain 3525 was assessed by monitoring the populations of 3525 and 3525.L on tomato, which is not a host for this pathogen. The mutant 3525.L was signi®cantly impaired in its ability to colonize tomato leaves compared with 3525, indicating that alginate functions in the survival of strain 3525 on leaf surfaces. The contribution of alginate to the virulence of strain 3525 was evaluated by comparing the population dynamics and symptom development of 3525 and 3525.L in bean leaves. Although 3525.L retained the ability to form lesions on bean leaves, symptoms were less severe, and the population was signi®cantly reduced in comparison with 3525. These results indicate that alginate contributes to the virulence of P. syringae pv. syringae 3525, perhaps by facilitating colonization or dissemination of the bacterium in planta.

The alternative sigma factor AlgT, but not alginate synthesis, promotes in planta multiplication of Pseudomonas syringae pv. glycinea

“…In contrast to our findings, a different in planta scenario had been previously described for an algL " alginate mutant in the related phytopathogen P. syringae pv. syringae FF5 (Yu et al, 1999). A slightly lower in planta population size for PG4180.muc.alg in comparison to PG4180.muc could be assigned to lack of alginate biosynthesis and was also found in PG4180.alg, compared to its parental strains.…”

“…A positive correlation between virulence of P. syringae and the quantity of alginate produced in planta has been demonstrated (Gross & Rudolph, 1987b;Osman et al, 1986). The biosynthetic route to alginate in P. syringae is similar to that established for P. aeruginosa, where alginate synthesis has been studied extensively and where it functions as a virulence factor in strains infecting the lungs of cystic fibrosis patients (Fett et al, 1992;Fialho et al, 1990;Peñaloza-Vázquez et al, 2004Pier, 1998;Yu et al, 1999). Genes encoding enzymes of alginate biosynthesis in P. aeruginosa and P. syringae are organized in an operon (algD-algA), with the exception of algC (Chitnis & Ohman, 1993;Peñaloza-Vázquez et al, 2004Zielinski et al, 1991).…”

“…syringae alginate production has been associated with increased epiphytic fitness, virulence, resistance to desiccation and toxic molecules, dissemination in planta (Rudolph et al, 1994;Yu et al, 1999) and the induction of water-soaked lesions on infected leaves (Fett & Dunn, 1989). A positive correlation between virulence of P. syringae and the quantity of alginate produced in planta has been demonstrated (Gross & Rudolph, 1987b;Osman et al, 1986).…”

AlgR functions in algC expression and virulence in Pseudomonas syringae pv. syringae

“…This is consistent with an earlier study where an alginate-defective mutant of P. syringae pv. syringae 3525 (a bean pathogen) was impaired in epiphytic fitness (Yu et al, 1999).…”

“…Alginate, a co-polymer of O-acetylated b-1,4-linked D-mannuronic acid and L-guluronic acid, has been reported to function in the virulence of P. syringae by facilitating dissemination of the bacterium in planta and by enhancing epiphytic fitness Yu et al, 1999). Alginate biosynthesis has been extensively studied in Pseudomonas aeruginosa, where it functions as a major virulence factor in strains infecting the lungs of cystic fibrosis (CF) patients (Lyczak et al, 2002).…”