Mineral–Water Hydrogen Generation and Microbial Activity Under LHS 1140 b-Inspired Aqueous Conditions: Implications for Habitability

Water-rich planetary environments provide a relevant framework for investigating how localized mineral–water reactions and reducing aqueous conditions may influence biological processes. In the present study, an LHS 1140 b-inspired terrestrial aqueous framework was developed to examine Mg⁰-mediated molecularhydrogen generation and microbial responses under defined mineral–water conditions. The reaction of zero-valent magnesium with water produced an H₂-containing reducing aqueous phase and hydrated/hydroxylated Mg–O/Mg–OH-containing solid products, as characterized by direct physicochemical measurements and Fourier Transform Infrared (FT-IR) spectroscopy. The aerobic facultative methylotrophic bacterium Brevibacterium methylicum B-5652 was employed as a terrestrial microbial test system for methanol-dependent RuMP C₁ assimilation. In the H₂-associated M9 condition, wet biomass reached 217.3 ± 4.1 g·L⁻¹ compared with 201.4 ± 2.9 g·L⁻¹ in the reference medium, corresponding to a 7.9% increase, whereas the bicarbonate–mineral aqueous condition yielded 190.5 ± 3.9 g·L⁻¹ (94.6% of the reference biomass). Lag-phase and generation-time differences were comparatively smaller. L-Phenylalanine formation followed the general pattern of biomass accumulation, demonstrating preservation of methanol-dependent biosynthetic activity across the investigated aqueous conditions. Complementary short-term assays with four Saccharomyces cerevisiae strains showed no obvious reduction in subsequent growth after 30 min exposure to H₂-containing water. Previous studies of hot mineral-water systems have independently demonstrated biologically relevant responses at approximately 1–2 ppm H₂ and hydrogen-associated amino-acid microstructural organization. The present findings therefore establish an experimentally accessible framework linking mineral–water H₂ generation, mineral-surface transformation, microbial biomass formation, and C₁-dependent biosynthetic activity, without assuming that the laboratory system reproduces the complete atmospheric or oceanic environment of LHS 1140 b.