Response of Escherichia coli to hydrogen nanobubbles: an in vitro evaluation using synchrotron infrared spectroscopy

Hydrogen (H₂)-rich water, an apparent source of molecular H₂, is an emerging functional drink with many purported benefits for human health (Yang et al., 2020; Ostojic, 2021). The preventive and therapeutic effects of H₂ on various pathological processes have been intensively investigated in numerous clinical trials; it is commonly believed that the beneficial effects are mainly attributed to its selective antioxidant and anti-inflammatory properties (Lee et al., 2015; Ohta, 2015; LeBaron et al., 2019; Qiu et al., 2020). In recent years, a handful of rodent studies revealed that exogenous H₂ can affect the gut microbiota (Sha et al., 2018; Valdes et al., 2018). For example, H₂ was reported to induce a higher abundance of butyrate-producing bacteria in a rat model of Parkinson's disease (Bordoni et al., 2019). Recent first-in-human trials have explored the effects of the long-term consumption of H₂-rich water on antioxidant activity and the gut flora (Sha et al., 2018; Suzuki et al., 2018). Although these promising results suggest that the intestinal microbiota may be another plausible target for molecular H₂, more studies are highly warranted to explain the mechanism(s) of H₂ action on bacterial growth and functions.