Sulfate reduction and homoacetogenesis at various hypersaline conditions: Implications for H2 underground gas storage

While interest in underground gas storage (UGS) of hydrogen (H 2 ) salt caverns is increasing a growing H economy, knowledge the microbial communities inhabiting those hypersaline environments still scarce. High concentrations and limited availability carbon (C) sources cavern reduce growth rates metabolic activities. Growth conditions potentially change once stored caverns. universal electron donor that can facilitate autotrophic subsequently heterotrophs. In this study, mixed culture enriched from UGS sites was investigated microcosm experiments with atmosphere, testing effect different C on methanogenesis, sulfate reduction homoacetogenesis. Sulfate, acetate lactate were quantified throughout time span 125 days incubation correlations community structure function explored through 16S rRNA gene-based amplicon sequencing at end experiment. Many sequence variants (ASVs) only assigned to family or order level, reflecting large number ASVs belong previously undescribed taxa. At 4.4 M NaCl, close brine salinity, members Desulfovibrionales absent when no source other than CO offered as sole source. This line finding occurred these conditions. Acetogenic Halanaerobiia dominated high salinity levels. Based metagenome four selected samples, we found acetogenesis relies activity halophilic homoacetogen, Acetohalobium sp. most likely be associated so far member Desulfonatronovibrionales. We further discuss discrepancy between heterotrophic conditions, while observed under although produced homoacetogenic . For application , means presence aforementioned microorganisms must investigated, they eventually lead formation allow relevant concentrations.