Biological functions of nirS in Pseudomonas aeruginosa ATCC 9027 under aerobic conditions

Through our previous study, we found an up-regulation in the expression of nitrite reductase (nirS) in the isothiazolone-resistant strain of Pseudomonas aeruginosa. However, the definitive molecular role of nirS in ascribing the resistance remained elusive. In the present study, the nirS gene was deleted from the chromosome of P. aeruginosa ATCC 9027 and the resulting phenotypic changes of Delta nirS were studied alongside the wild-type (WT) strain under aerobic conditions. The results demonstrated a decline in the formations of biofilms but not planktonic growth by Delta nirS as compared to WT, especially in the presence of benzisothiazolinone (BIT). Meanwhile, the deletion of nirS impaired swimming motility of P. aeruginosa under the stress of BIT. To assess the influence of nirS on the transcriptome of P. aeruginosa, RNA-seq experiments comparing the Delta nirS with WT were also performed. A total of 694 genes were found to be differentially expressed in Delta nirS, of which 192 were up-regulated, while 502 were down-regulated. In addition, these differently expressed genes were noted to significantly enrich the carbon metabolism along with glyoxylate and dicarboxylate metabolisms. Meanwhile, results from RT-PCR suggested the contribution of mexEF-oprN to the development of BIT resistance by Delta nirS. Further, c-di-GMP was less in Delta nirS than in WT, as revealed by HPLC. Taken together, our results confirm that nirS of P. aeruginosa ATCC 9027 plays a role in BIT resistance along with biofilm formation and further affects several metabolic patterns under aerobic conditions.