The Double-Edged Sword of Bacterial Nitric Oxide: From Fundamental Conflict to Engineered Therapeutics

Abstract

Nitric oxide (NO) is a multifaceted signaling molecule with important roles in both prokaryotic and eukaryotic systems. In bacteria, NO is produced endogenously through several biochemical pathways, including the enzymatic activity of bacterial NO synthases (bNOS) and the respiratory denitrification enzymes known as nitrite reductases (NirK and NirS). These systems contribute to bacterial energy metabolism, stress responses, and intercellular signaling. Depending on its concentration, source, and biological context, bacterial NO may promote biofilm formation and antibiotic tolerance, whereas host-derived NO can contribute to bacterial clearance. Major bacterial genera reported to produce NO include Bacillus subtilis, Deinococcus radiodurans, Geobacillus stearothermophilus, Lactobacillus fermentum, and Staphylococcus aureus, as well as Neisseria, Haemophilus, Veillonella, Granulicatella, and Prevotella spp. Recent advances in molecular biology and synthetic biology have greatly expanded the repertoire of available approaches for engineering bacteria to produce NO at high or controllable biological levels. For example, Escherichia coli Nissle 1917 and Lactobacillus species have been engineered to express inducible NOS enzymes under tightly regulated promoters. Engineered therapeutics, including selective bNOS inhibitors, nanoparticle-delivered NO donors, and NO-antibiotic synergistic regimens, may harness this duality for therapeutic benefit. To exploit concentration-dependent effects that trigger biofilm dispersal at nanomolar levels followed by bactericidal bursts, next-generation NO-based therapies will need to achieve precise spatial and temporal control. Key areas of progress include decoding how bacteria detect NO from both host and self, engineering smart biomaterials that release NO in response to the infection microenvironment, and developing bNOS inhibitors that selectively target bacterial isoforms. In addition, modulation of NO in conjunction with other gasotransmitter systems, such as H₂S and CO, together with NO-sensing probiotic therapeutics and synthetic biology approaches, may offer promising strategies for improving NO production and therapeutic application.