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Abstract:

Microbial life in Earth’s deep subsurface is currently known to reach depths of several kilometers within the continental crust. Methanotrophs are a subset of a physiological group of bacteria known as methylotrophs. Phylogenetically, methanotrophs belong to α- or γ- Proteobacteria, but there are also some representatives affiliated as Verrucomicrobia and NC10 phylum. Halotolerant and halophilic methanotrophs have been isolated from seawater, coastal lagoons, and several soda lakes. The aim of this study was to assess the possibility of oxidation of methane by microorganisms inhabiting the rocks surrounding salt deposits in the “Wieliczka” Salt Mine. The research material was taken from rocks lying in the immediate vicinity of the “Wieliczka” Salt Mine deposits. The research material was diverse in terms of the depth, lithology, and surrounding salt deposit types. The determinations of the ability of the microbial community from the tested rocks to oxidize methane were performed by incubation of a crushed rock under methane atmosphere (10 % (v/v)). Gas composition was measured by the gas chromatography technique. Methanotrophic activity was determined based on the dynamics of methane consumption and expressed as micromole per grams of dry weight of sample per day. The results show the dynamics of CH₄, O₂, CO₂, and N₂ concentrations in the gaseous phase during incubation of the rocks. This revealed that methane uptake in the investigated samples is due to the activity of methanotrophs. In all incubated samples, utilization of CH₄ and O₂ was observed after 77 days, which was confirmed by the parallel drop in the concentration of those gases and simultaneous growth of the CO₂ ratio. The highest methanotrophic activity (0.252±0.090 μMCH4 gdw^-1 day^-1) was found in W4 rock (siltstones with veins of fibrous salt and lenses of anhydrite), characterized by pH of cca. 7.43±0.004, Eh at the level of 374±1.36 mV, and salinity of cca. 3.6 %.