Hydrogen-powered bacteria enhance organic micropollutant degradation under starvation conditions

Organic micropollutants (OMPs) occur in natural aquatic environments at trace concentrations with suspected adverse effects on the ecosystem and human health. Microbial biodegradation plays a crucial role in OMP-elimination from drinking water resources. However, long-term OMP-biodegradation remains challenging since the metabolic activity of degrading strains is restricted by energy-limited conditions in treatment systems. Molecular hydrogen (H₂) has been identified as a universally available energy source utilized by various bacteria under nutrient-starved conditions, and it can be hypothesized that H₂ might also support OMP-degrading microbes when other energy carriers are scarce. The potential of H₂ as a supporting energy source for OMP-degradation was tested by examining its effect on the biodegradation of 2,6-dichlorobenzamide (BAM) by Aminobacter niigataensis MSH1 and on the physiological status of the MSH1 cells during both nongrowth-linked (500 μg BAM/L) and growth-linked (10,000 μg BAM/L) regimes. MSH1 cells used as inoculum were either not or pre-exposed to H₂ and were harvested at different growth phases. During the nongrowth-linked BAM biodegradation, MSH1 pre-exposed to H₂ exhibited a 1.2 to 1.5-fold higher initial specific BAM biodegradation rate, resulting in more rapid BAM removal, likely due to the retention of more metabolically active cells, as suggested by a cell vitality assay. During the growth-linked biodegradation, MSH1 pre-exposed to H₂ demonstrated accelerated growth with a 1.5-fold higher maximum specific growth rate, which coincided with an improved BAM removal. The positive effects of H₂ were only evident for MSH1 cells harvested either at the stationary and/or starvation phase. Evidence of H₂ metabolism was supported by H₂ consumption measurements. Collectively, this study reveals that microbial H₂ metabolism enables OMP-degrading bacteria to sustain metabolic activity under starvation conditions, offering a novel strategy to enhance long-term OMP-biodegradation.