USC-γ cluster dominates the methanotroph communities in the karst Heshang Cave

Abstract

Microorganisms are thought to play a critical role in methane consumption in karst caves, however, the presence and diversity of methane-oxidizing bacteria (MOB) are still mysterious. In Heshang Cave, CH₄ concentration decreases from 1.9 ppm at the entrance to 0.65 ppm into the cave. To explore the presence and diversity of MOB in this cave, weathered rocks and sediment samples were collected across the cave and subject to molecular analysis. The abundances of MOB were 10⁷–10⁸ copies g⁻¹ dry sample via quantification of the pmoA gene, which are comparable to or even higher than those reported in other terrestrial environments and account for up to 20% of the total microbial communities. Phylogenetically MOB communities were dominated by the 'high-affinity' upland soil γ cluster (USCγ), although the predominance of type Ia MOB was also detected in the permanent waterlogged stream sediment. The estimated CH₄ oxidation potential varied dramatically among samples in the range of 0.6–80 CH₄ m⁻³ d⁻¹. Collectively, this study provided compelling evidence that the high-affinity MOB capable of oxidizing methane at the atmospheric level are present in Heshang Cave, which may play an important role in the methane consumption and supports karst caves as an important atmospheric CH₄ sink.

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