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/geothermal soils are not only a source of methane,but also sites of methanotrophic activity. Methanotrophs are able to consume 10-40 Tg ofCH4 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 ofPantelleria island (Italy), Favara Grande, whose total methane emission was previouslyestimated in about 2.5 Mg a-1 (t a-1). Laboratory incubation experiments with three top-soilsamples from Favara Grande indicated methane consumption values up to 59.2 nmol g-1soil 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 and the maximum methane consumption wasmeasured in the top-soil layer and values >6.23 nmol g-1 h-1 were still detected up to adepth of 13 cm. The highest consumption rate was measured at 37°C, but a still detectableconsumption at 80°C (>1.25 nmol g -1 h-1) was recorded.The soil total DNAs extracted from the three samples were probed by PCR using standardproteobacterial primers and newly designed verrucomicrobial primers, targeting the uniquemethane monooxygenase gene pmoA; the presence of methanotrophs was detected insites FAV2 and FAV3, but not in FAV1, where harsher chemical-physical conditions andnegligible methane oxidation were detected. The pmoA gene libraries from the most activesite FAV2 pointed out a high diversity of gammaproteobacterial methanotrophs, distantlyrelated to Methylococcus/Methylothermus genera and the presence of the newlydiscovered acido-thermophilic methanotrophs Verrucomicrobia. Alphaproteobacteria of thegenus Methylocystis were isolated from enrichment cultures, under a methane containingatmosphere at 37°C. The isolates grow at a pH range from 3.5 to 8, temperatures of 18 –45 °C and consume 160 nmol of CH 4 h-1 ml-1 of culture. Soils from Favara Grande showedthe largest diversity of methanotrophic bacteria until now detected in a geothermal soil.While methanotrophic Verrucomicrobia are reported to dominate highly acidic geothermalsites, our results suggest that slightly acidic soils, in high enthalpy geothermal systems,host a more diverse group of both culturable and uncultivated methanotrophs.
|Numero di pagine||11|
|Stato di pubblicazione||Published - 2014|
All Science Journal Classification (ASJC) codes