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Titel |
High diversity of methanotrophic bacteria in geothermal soils affected by high methane fluxes |
VerfasserIn |
Walter D'Alessandro, Antonina Lisa Gagliano, Paola Quatrini, Francesco Parello |
Konferenz |
EGU General Assembly 2014
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 16 (2014) |
Datensatznummer |
250089488
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Publikation (Nr.) |
EGU/EGU2014-3692.pdf |
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Zusammenfassung |
Volcanic and geothermal systems emit endogenous gases by widespread degassing from soils,
including CH4, a greenhouse gas 25 times as potent as CO2. Recently, it has been
demonstrated that volcanic/geothermal soils act as source, but also as biological filter
for methane release to the atmosphere. For long time, volcanic/geothermal soils
has been considered inhospitable for methanotrophic microorganisms, but new
extremophile methanotrophs belonging 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/geothermal areas and biological methane oxidation, by
investigating a geothermal site of Pantelleria island (Italy). Pantelleria Island hosts a high
enthalpy geothermal system characterized by high temperature, high CH4 and very
low H2S fluxes. Such characteristics are reflected in potentially great supply of
methane for methanotrophs and scarce presence of inhibitors of their activity (H2S
and NH3) in the Pantelleria soils. Potential methanotrophic activity within these
soils was already evidenced by the CH4/CO2 ratio of the flux measurements which
was lower than that of the 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 hydrothermal
area of Pantelleria, showed very high methane consumption rates (up to 9500 ng
CH4 h-1 g-1). Furthermore, microbiological and culture-independent molecular
analyses allowed to detect the presence of methanotrophs affiliated to Gamma- and
Alpha-Proteobacteria and to the newly discovered acidothermophilic methanotrophs
Verrucomicrobia. Culturable methanotrophic Alpha-proteobacteria of the genus
Methylocystis were isolated by enrichment 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 verrucomicrobial
methanotrophs 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 in the same geothermal site. The presence of proteobacterial
methanotrophs was quite unexpected because they are generally considered not
adapted to live in such harsh environments. Their presence at Favara Grande could be
explained 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 so high, thriving on
the abundant upraising methane. Understanding the ecology of methanotrophy in
geothermal sites will increase our knowledge of their role in methane emissions to the
atmosphere. |
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