The histone-like protein AlgP regulon is distinct in mucoid and nonmucoid Pseudomonas aeruginosa and does not include alginate biosynthesis genes

The opportunistic bacterial pathogenPseudomonas aeruginosacauses acute and chronic infections that are notoriously difficult to treat. In people with cystic fibrosis,P. aeruginosacan cause lifelong lung infections, and isolation of mucoidP. aeruginosa, resulting from the overproduction of alginate, is associated with chronic infection. The histone-like protein AlgP has previously been implicated in the control of alginate gene expression in mucoid strains, but this regulation is unclear. To explore AlgP in further detail, we deletedalgPin mucoid strains and demonstrated that the deletion ofalgPdid not result in a nonmucoid phenotype or a decrease in alginate production. We showed that thealgPpromoter is expressed by both the nonmucoid strain PAO1 and the isogenic mucoid strain PDO300, suggesting that there may be genes that are differentially regulated between these strains. In support of this, using RNA sequencing, we identified a small AlgP regulon that has no significant overlap between PAO1 and PDO300 and established that alginate genes were not differentially regulated by the deletion ofalgP. Of note, we found that deletingalgPin PAO1 increased expression of the nitric oxide operonnorCBDand the nitrous oxide reductase genesnosRZand subsequently promoted growth of PAO1 under anaerobic conditions. Altogether, we have defined a narrow regulon of genes controlled by AlgP and provided evidence that alginate production is not greatly affected by AlgP, countering the long-standing premise in the field.