Upland soil cluster γ dominates the methanotroph communities in the karst Heshang Cave

ABSTRACT

Microorganisms are thought to play a critical role in methane (CH₄) consumption in karst caves and yet the presence and diversity of methane-oxidizing bacteria (MOB) remain a mystery. In Heshang Cave, CH₄ concentration decreases from 1.9 ppm at the entrance to 0.65 ppm inside the cave. To explore the presence and diversity of MOB in this cave, weathered rocks and sediment samples were collected from the cave and subjected 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 cluster γ (USCγ), although the predominance of Type Ia MOB was also detected in the permanently 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 provides compelling evidence that the high-affinity MOB capable of oxidizing CH₄ at the atmospheric level are present in Heshang Cave, which may play an important role in the CH₄ consumption, and supports karst caves as important atmospheric CH₄ sinks.

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