Molecular characterization of the extracellular matrix in a Pseudomonas putida dsbA mutant: implications for acidic stress defense and plant growth promotion

The Pseudomonas putida dsbA mutant displays enhanced extracellular matrix production, which promotes biofilm formation. Here we confirmed that the extracellular matrix consists of both capsular polysaccharides and exopolysaccharides. However, the carbohydrate composition of the P. putida dsbA mutant matrix was shown to be similar to that of the wild-type strain. Our data indicate that the overproduced matrix itself, rather than alterations in the matrix composition, promotes biofilm formation in the P. putida dsbA mutant. Moreover, the mutant was more sensitive than the wild-type to alkali stress (pH 9.0 to 10.0), but not to acidic stress (pH 5.0). Interestingly, acidic stress stimulated polysaccharide production and pellicle formation, while these changes were recovered to the level of the wild-type under alkali conditions in the P. putida dsbA mutant. Enhanced biofilm formation of the dsbA mutant increased the efficiency with which P. putida attached to tomato and pepper seeds, which have longer germinated roots than the wild-type strain. This phenomenon could not be observed in the cucumber plant, which suggests that each plant seed has a different effect on the attachment of P. putida. Interestingly, this increased attachment to plant seeds resulted in more root colonization and plant growth promotion. The findings of this study suggested that the overproduced extracellular matrix caused by deletion of the dsbA gene could have pleiotropic effect on P. putida phenotypes, including acidic stress defense and plant growth promotion.