Characterization of the Role of dadA in Pseudomonas aeruginosa Virulence Factor Production
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Chronic Pseudomonas aeruginosa infections remain the leading cause of lung dysfunction and mortality in Cystic Fibrosis (CF) patients. Many other bacteria reside within the CF lung, but P. aeruginosa utilizes novel strategies that allow it to colonize the CF lung as the predominant bacterial pathogen. We determined previously that FRD1, a CF P. aeruginosa isolate, requires dadA for optimal hydrogen cyanide (HCN) production, while PAO1, an acute isolate of P. aeruginosa, does not. In order to better understand the increased significance of dadA in FRD1 physiology, we characterized the contribution of the dad operon to virulence factor production by FRD1 and PAO1. The dad operon contains two genes, dadA and dadX, which encode for enzymes required for the catabolism of alanine. dadA encodes for a putative D-amino acid dehydrogenase, while dadX encodes for an alanine racemase. In this study, we determined that dadA is required for optimal production of alginate, pyocyanin, pyoverdine, rhamnolipid, and biofilm formation by FRD1, as well as optimal virulence of FRD1 in an alfalfa seedling model of infection, while dadX is not. In contrast, dadA is required only for optimal rhamnolipid production by PAO1. In an attempt to explain the dadA phenotype, L- and D-alanine levels were quantitated, but the results were inconclusive. Taken together, the results indicate that dadA plays a pleiotropic role in the production of important virulence factors by CF isolates of P. aeruginosa.