Methane oxidation and methylotroph population dynamics in groundwater mesocosms

Abstract

Summary Extraction of natural gas from unconventional hydrocarbon reservoirs by hydraulic fracturing raises concerns about methane migration into groundwater. Microbial methane oxidation can be a significant methane sink. Here, we inoculated replicated, sand‐packed, continuous mesocosms with groundwater from a field methane release experiment. The mesocosms experienced thirty‐five weeks of dynamic methane, oxygen and nitrate concentrations. We determined concentrations and stable isotope signatures of methane, carbon dioxide and nitrate and monitored microbial community composition of suspended and attached biomass. Methane oxidation was strictly dependent on oxygen availability and led to enrichment of 13C in residual methane. Nitrate did not enhance methane oxidation under oxygen limitation. Methylotrophs persisted for weeks in the absence of methane, making them a powerful marker for active as well as past methane leaks. Thirty‐nine distinct populations of methylotrophic bacteria were observed. Methylotrophs mainly occurred attached to sediment particles. Abundances of methanotrophs and other methylotrophs were roughly similar across all samples, pointing at transfer of metabolites from the former to the latter. Two populations of Gracilibacteria (Candidate Phyla Radiation) displayed successive blooms, potentially triggered by a period of methane famine. This study will guide interpretation of future field studies and provides increased understanding of methylotroph ecophysiology.

Hydrogen and dark oxygen drive microbial productivity in diverse groundwater ecosystems

“…The coexistence of these guilds was previously observed in a methane-rich shallow aquifer ( 37 ) as well as in methylotrophic micro-biomes of mesocosms ( 38 ). Aerobic methane oxidizers of the genus Crenothrix ( 39 ) were the fourth most abundant and occurred in almost half of the samples (45 of 109, Fig S8).…”

Hydrogen and dark oxygen drive microbial productivity in diverse groundwater ecosystems

“…Denitrification by Methylotenera was reported previously 39 and hence Methylotenera could provide nitrite to Methylobacter , while Methylobacter provides methanol to Methylotenera . Complementary interactions between Methylobacter and Methylotenera were observed in a methane-rich shallow aquifer 40 , a lake 41 as well as in methanotrophic enrichment cultures 42 . The metabolic capabilities of the consortium however suggest that molecular oxygen needs to be available to catalyze the initial activation of methane, even if subsequent steps can be coupled to denitrification.…”

Procaryotic Diversity and Hydrogenotrophic Methanogenesis in an Alkaline Spring (La Crouen, New Caledonia)

“…In field and groundwater CH 4 -spiked mesocosms studies, the growth of Ca. Gracilibacteria appeared to be stimulated by a period of CH 4 starvation (after CH 4 injection was stopped), suggesting they could benefit from the disappearance and death of other CH 4 -dependent populations [ 77 , 78 ]. Genomic and metagenomic analyses of Ca.…”

“…Gracilibacteria (OTU #52) co-exists with Methyloversatilis spp. (OTU #5158), which have been noted as the most persistent methylotrophs after many weeks of CH 4 starvation in groundwater mesocosms [ 78 ]. This observation is consistent with the CH 4 below the detection limit in our samples, even though it was previously detected at La Crouen spring [ 3 ].…”