Pseudomonas aeruginosa AlgU Contributes to Posttranscriptional Activity by Increasing rsmA Expression in a mucA22 Strain

Pseudomonas aeruginosa thrives in multiple environments and is capable of causing life-threatening infections in immunocompromised patients. RsmA is a posttranscriptional regulator that controls virulence factor production and biofilm formation. In this study, we investigated the expression and activity ofrsmA and the protein that it encodes, RsmA, inP. aeruginosa mucA mutant strains, which are common in chronic infections. We determined that AlgU regulates a previously unknownrsmA promoter inP. aeruginosa . Western blot analysis confirmed that AlgU controlsrsmA expression in both a laboratory strain and a clinical isolate. RNase protection assays confirmed the presence of tworsmA transcripts and suggest that RpoS and AlgU regulatersmA expression. Due to the increased amounts of RsmA inmucA mutant strains, a translational leader fusion of the RsmA target,tssA1 , was constructed and tested inmucA ,algU ,retS ,gacA , andrsmA mutant backgrounds to examine posttranscriptional activity. From these studies, we determined that RsmA is active inmucA22 mutants, suggesting a role for RsmA inmucA mutant strains. Taken together, we have demonstrated that AlgU controlsrsmA transcription and is responsible for RsmA activity inmucA mutant strains. We propose that RsmA is active inP. aeruginosa mucA mutant strains and that RsmA also plays a role in chronic infections.IMPORTANCE P. aeruginosa causes severe infections in immunocompromised patients. The posttranscriptional regulator RsmA is known to control virulence and biofilm formation. We identify a newrsmA promoter and determine that AlgU is important in the control ofrsmA expression. MutantmucA strains that are considered mucoid were used to confirm increasedrsmA expression from the AlgU promoter. We demonstrate, for the first time, that there is RsmA activity in mucoidP. aeruginosa strains. Our work suggests that RsmA may play a role during chronic infections as well as acute infections.