Nitric oxide donor sodium nitroprusside serves as a source of iron supporting Pseudomonas aeruginosa growth and biofilm formation

Biofilm dispersal agents, like nitric oxide (NO), restore antimicrobial effectiveness against biofilm infections by inducing bacteria to shift from a biofilm to a planktonic state, thereby overcoming the antimicrobial tolerance typically associated with biofilms. Sodium nitroprusside (SNP) is a widely used NO donor for investigating the molecular mechanisms underlying NO-mediated biofilm dispersal in the nosocomial pathogen Pseudomonas aeruginosa . However, the biofilm effects of SNP are variable depending on the in vitro experimental conditions, with some studies reporting enhanced growth in both planktonic and biofilm forms instead of dispersal. These discrepancies suggest that SNP affects P. aeruginosa biofilm-residing cells beyond the release of NO. In this study, we compared SNP with another NO donor, Spermine NONOate, to systematically contrast their effects on biofilm and planktonic cultures of P. aeruginosa . We found that SNP, but not Spermine NONOate, increased the biomass of P. aeruginosa biofilms in microplate cultures. This effect was also observed when biofilms were supplemented with iron. Additionally, supplementation with SNP rescued the planktonic growth of P. aeruginosa in iron-depleted media, similar to FeSO ₄ supplementation, suggesting that SNP may serve as an iron source. Our findings suggest that SNP’s potential as an NO agent used for biofilm dispersal may be confounded by its role in promoting both biofilm and planktonic growth through its iron centre. Our study cautions investigators using SNP for studying NO-mediated biofilm dispersal.