High diversity of methanotrophic bacteria in geothermal soils affected byhigh methane fluxes

Risultato della ricerca: Other

Abstract

Volcanic and geothermal systems emit endogenous gases by widespread degassing from soils, including CH4, agreenhouse gas 25 times as potent as CO2. Recently, it has been demonstrated that volcanic/geothermal soils actas source, but also as biological filter for methane release to the atmosphere. For long time, volcanic/geothermalsoils has been considered inhospitable for methanotrophic microorganisms, but new extremophile methanotrophsbelonging to Verrucomicrobia were identified in three different areas (Pozzuoli, Italy; Hell’s Gate, New Zealand;Kamchatka, Russia), explaining anomalous behaviours in methane leakages of several geothermal/volcanic sites.Our aim was to increase the knowledge of the relationship between methane emissions from volcanic/geothermalareas and biological methane oxidation, by investigating a geothermal site of Pantelleria island (Italy). PantelleriaIsland hosts a high enthalpy geothermal system characterized by high temperature, high CH4 and very low H2Sfluxes. Such characteristics are reflected in potentially great supply of methane for methanotrophs and scarce presenceof inhibitors of their activity (H2S and NH3) in the Pantelleria soils. Potential methanotrophic activity withinthese soils was already evidenced by the CH4/CO2 ratio of the flux measurements which was lower than that ofthe respective fumarolic manifestations indicating a loss of CH4 during the gas travel towards the earth’s surface.In this study laboratory incubation experiments using soils sampled at Favara Grande, the main hydrothermalarea of Pantelleria, showed very high methane consumption rates (up to 9500 ng CH4 h1 g1). Furthermore,microbiological and culture-independent molecular analyses allowed to detect the presence of methanotrophsaffiliated to Gamma- and Alpha-Proteobacteria and to the newly discovered acidothermophilic methanotrophsVerrucomicrobia. Culturable methanotrophic Alpha-proteobacteria of the genus Methylocystis were isolated byenrichment cultures. The isolates showed a wide range of tolerance to pH (3.5 – 8) and temperatures (18 – 45 C),and an average methane oxidation rate of 450 ppm/h. A larger diversity of proteobacterial and verrucomicrobialmethanotrophs was detected by the amplification of the methane mono-oxygenase gene pmoA.This study demonstrates the coexistence of both the methanotrophic phyla Verrucomicrobia and Proteobacteria inthe same geothermal site. The presence of proteobacterial methanotrophs was quite unexpected because they aregenerally considered not adapted to live in such harsh environments. Their presence at Favara Grande could beexplained by not so low soil pH values (> 5) of this specific geothermal site and by the high methane availability.Such species could have found their niches in the shallowest part of the soils, were the temperatures are not sohigh, thriving on the abundant upraising methane. Understanding the ecology of methanotrophy in geothermalsites will increase our knowledge of their role in methane emissions to the atmosphere.
Lingua originaleEnglish
Pagine3692-1-3692-1
Numero di pagine1
Stato di pubblicazionePublished - 2014

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