The effect of polyhydroxyalkanoates in PA23 biofilm formation, stress endurance, and interaction with the protozoan predator .

PA23 is a biocontrol agent capable of protecting canola against the fungal pathogen . In addition to producing antifungal compounds, this bacterium synthesizes and accumulates polyhydroxyalkanoate (PHA) polymers as carbon and energy storage compounds. Because the role of PHA in PA23 physiology is currently unknown, we investigated the impact of this polymer on stress resistance, adherence to surfaces, and interaction with the protozoan predator . Three PHA biosynthesis mutants were created, PA23, PA23, and PA23, which accumulated reduced PHA. Our phenotypic assays revealed that PA23 produced less phenazine (PHZ) compared with the wild type (WT) and the and mutants. All three mutants exhibited enhanced sensitivity to UV irradiation, starvation, heat stress, cold stress, and hydrogen peroxide. Moreover, motility, exopolysaccharide production, biofilm formation, and root attachment were increased in strains with reduced PHA levels. Interaction studies with the amoeba revealed that the WT and the and mutants were consumed less than the mutant, likely due to decreased PHZ production by the latter. Collectively these findings indicate that PHA accumulation enhances PA23 resistance to a number of stresses in vitro, which could improve the environmental fitness of this bacterium in hostile environments.