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Volume 11, issue 20
Biogeosciences, 11, 5865–5875, 2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 11, 5865–5875, 2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 22 Oct 2014

Research article | 22 Oct 2014

Methanotrophic activity and diversity of methanotrophs in volcanic geothermal soils at Pantelleria (Italy)

A. L. Gagliano1,2, W. D'Alessandro3, M. Tagliavia2,*, F. Parello1, and P. Quatrini2 A. L. Gagliano et al.
  • 1Department of Earth and Marine Sciences (DiSTeM), University of Palermo, Via Archirafi 36, 90123 Palermo, Italy
  • 2Department of Biological, Chemical and Pharmaceutical Sciences and Technologies (STEBICEF), University of Palermo, Viale delle Scienze, Bldg 16, 90128 Palermo, Italy
  • 3Istituto Nazionale di Geofisica e Vulcanologia (INGV) – Sezione di Palermo, Via U. La Malfa 153, 90146 Palermo, Italy
  • *present address: Istituto per l'Ambiente Marino Costiero (CNR-IAMC) U.S.O. of Capo Granitola, Via del Mare 3, Torretta-Granitola, Mazara, Italy

Abstract. Volcanic and geothermal systems emit endogenous gases by widespread degassing from soils, including CH4, a greenhouse gas twenty-five times as potent as CO2. Recently, it has been demonstrated that volcanic or geothermal soils are not only a source of methane, but are also sites of methanotrophic activity. Methanotrophs are able to consume 10–40 Tg of CH4 a−1 and to trap more than 50% of the methane degassing through the soils. We report on methane microbial oxidation in the geothermally most active site of Pantelleria (Italy), Favara Grande, whose total methane emission was previously estimated at about 2.5 Mg a−1 (t a−1). Laboratory incubation experiments with three top-soil samples from Favara Grande indicated methane consumption values of up to 59.2 nmol g−1 soil d.w. h−1. One of the three sites, FAV2, where the highest oxidation rate was detected, was further analysed on a vertical soil profile, the maximum methane consumption was measured in the top-soil layer, and values greater than 6.23 nmol g−1 h−1 were still detected up to a depth of 13 cm. The highest consumption rate was measured at 37 °C, but a still detectable consumption at 80 °C (> 1.25 nmol g−1 h−1) was recorded. The soil total DNA extracted from the three samples was probed by Polymerase Chain Reaction (PCR) using standard proteobacterial primers and newly designed verrucomicrobial primers, targeting the unique methane monooxygenase gene pmoA; the presence of methanotrophs was detected at sites FAV2 and FAV3, but not at FAV1, where harsher chemical–physical conditions and negligible methane oxidation were detected. The pmoA gene libraries from the most active site (FAV2) pointed to a high diversity of gammaproteobacterial methanotrophs, distantly related to Methylocaldum-Metylococcus genera, and the presence of the newly discovered acido-thermophilic Verrucomicrobia methanotrophs. Alphaproteobacteria of the genus Methylocystis were isolated from enrichment cultures under a methane-containing atmosphere at 37 °C. The isolates grow at a pH range of 3.5 to 8 and temperatures of 18–45 °C, and consume 160 nmol of CH4 h−1 mL−1 of culture. Soils from Favara Grande showed the largest diversity of methanotrophic bacteria detected until now in a geothermal soil. While methanotrophic Verrucomicrobia are reported as dominating highly acidic geothermal sites, our results suggest that slightly acidic soils, in high-enthalpy geothermal systems, host a more diverse group of both culturable and uncultivated methanotrophs.

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