Nitric oxide donor sodium nitroprusside serves as a source of iron supportingPseudomonas aeruginosagrowth 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 pathogenPseudomonas aeruginosa. However, the biofilm effects of SNP are variable depending on thein vitroexperimental conditions, with some studies reporting enhanced growth in both planktonic and biofilm forms instead of dispersal. These discrepancies suggest that SNP affectsP. aeruginosabiofilm-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 ofP. aeruginosa. We found that SNP, but not Spermine NONOate, increased the biomass ofP. aeruginosabiofilms in microplate cultures. This effect was also observed when biofilms were supplemented with iron. Additionally, supplementation with SNP rescued the planktonic growth ofP. aeruginosain iron-depleted media, similar to FeSO₄supplementation, 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.