Hydrogen sulfide produced by sulfate-reducing bacteria (SRB) in sewers causes odor problems and asset deterioration due to the sulfide-induced concrete corrosion. Free nitrous acid (FNA) was recently demonstrated as a promising antimicrobial agent to alleviate hydrogen sulfide production in sewers. However, details of the antimicrobial mechanisms of FNA are largely unknown. Here, we report the multiple-targeted antimicrobial effects of FNA on the SRB Desulfovibrio vulgaris Hildenborough by determining the growth, physiological, and gene expression responses to FNA exposure. The activities of growth, respiration, and ATP generation were inhibited when exposed to FNA. These changes were reflected in the transcript levels detected during exposure. The removal of FNA was evident by nitrite reduction that likely involved nitrite reductase and the poorly characterized hybrid cluster protein, and the genes coding for these proteins were highly expressed. During FNA exposure, lowered ribosome activity and protein production were detected. Additionally, conditions within the cells were more oxidizing, and there was evidence of oxidative stress. Based on an interpretation of the measured responses, we present a model depicting the antimicrobial effects of FNA on D. vulgaris. These findings provide new insight for understanding the responses of D. vulgaris to FNA and will provide a foundation for optimal application of this antimicrobial agent for improved control of sewer corrosion and odor management. S ulfate-reducing bacteria (SRB) are anaerobic chemoorganotrophic microorganisms that typically use sulfate as the terminal electron acceptor for respiration and generate energy with the production of hydrogen sulfide (2). In confined spaces, the production of hydrogen sulfide can cause odor and corrosion problems. This is particularly the case in sewers and inlet structures of wastewater treatment plants, where the oxidation of sulfide produces sulfuric acid, which corrodes the concrete surfaces of the sewer. This results in serious deterioration of sewer assets that requires very costly and demanding rehabilitation efforts (3, 4). Consequently, there is great interest in the efficient control of SRB and thereby minimizing hydrogen sulfide production in sewers.Various chemical dosing methods are used to lower hydrogen sulfide production in sewers, and four strategies currently used include sulfide oxidation by the injection of chemical oxidants, such as air, oxygen, or nitrate (5, 6); sulfide precipitation by addition of iron salts (7); application of magnesium hydroxide or lime to raise the wastewater pH and prevent the release of hydrogen sulfide (8); and inhibition of the activities of SRB to lessen the generation of hydrogen sulfide (9). However, to obtain the required sulfide control, these strategies require continuous chemical consumption and considerable operational costs (10).Free nitrous acid (FNA), the protonated form of nitrite, was recently demonstrated to be the true metabolic inhibitor behind the usu...
