# Successional Trajectories of Deep Subsurface Microbiomes in Response To Experimental Dihydrogen Injection

## TL;DR

Injecting dihydrogen into deep aquifers causes predictable shifts in microbial communities, with initial diversity loss followed by specific successional patterns.

## Contribution

The study reveals deterministic ecological succession in deep subsurface microbiomes following dihydrogen injection.

## Key findings

- Dihydrogen exposure consistently reduced fermentative ASVs due to environmental filtering.
- Hydrogenotrophic sulfate reducers initially dominated, followed by methanogenic archaea in some experiments.
- Succession patterns involving Thermodesulfovibrio and Methanothermobacter suggest deterministic processes.

## Abstract

Converting pre-existing gas storage facilities to dihydrogen storage raises critical questions about storage quality and dihydrogen consumption by prokaryotes. To investigate biologically driven changes during such transitions, we analyzed data from five dihydrogen pulse experiments conducted in pressurized bioreactors that replicate deep aquifer pressure and temperature conditions. Our goal was to determine whether consistent community-level responses to dihydrogen injection could be identified. We found that dihydrogen exposure consistently led to a decline in fermentative ASVs, likely driven by environmental filtering. Hydrogenotrophic sulfate reducers initially dominated in some experiments, with total sulfate depletion observed in certain cases, followed by the emergence of methanogenic archaea. In some instances, a succession pattern involving Thermodesulfovibrio and Methanothermobacter appeared across taxonomically distinct communities, suggesting deterministic ecological processes. Additionally, we observed potential dispersal limitation and selection pressures, possibly linked to pH shifts caused by autotrophy. These findings underscore the importance of considering microbial dynamics in dihydrogen storage strategies in deep aquifers and suggest that, despite initial variability, predictable ecological succession may occur under specific geochemical conditions.

The online version contains supplementary material available at 10.1007/s00248-026-02697-3.

Most of the time, the arrival of dihydrogen leads to a decline in diversity among microbial communities from deep environements.

Depending on sulfate concentration, two distinct community dynamics scenarios emerge.

The introduction of new nutrients in these environments stimulates microbial communities but does not alter their structure.

The online version contains supplementary material available at 10.1007/s00248-026-02697-3.