Methanotrophic activity and diversity of methanotrophs in volcanic geothermal soils at Pantelleria (Italy)
Volcanic and geothermal systems emit endogenous gases by widespread degassing from soils, including CH<sub>4</sub>, a greenhouse gas twenty-five times as potent as CO<sub>2</sub>. Recently, it has been demonstrated that volcanic or geothermal soils are not only a source of me...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-10-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/11/5865/2014/bg-11-5865-2014.pdf |
| Summary: | Volcanic and geothermal systems emit endogenous gases by widespread degassing
from soils, including CH<sub>4</sub>, a greenhouse gas twenty-five times as potent as
CO<sub>2</sub>. 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 CH<sub>4</sub> a<sup>−1</sup>
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<sup>−1</sup> (t a<sup>−1</sup>). Laboratory
incubation experiments with three top-soil samples from Favara Grande
indicated methane consumption values of up to 59.2 nmol g<sup>−1</sup> soil
d.w. h<sup>−1</sup>. 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<sup>−1</sup> h<sup>−1</sup> 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<sup>−1</sup>
h<sup>−1</sup>) 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 <i>pmoA</i>; 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 <i>pmoA</i> gene libraries from the most active site (FAV2) pointed to
a high diversity of gammaproteobacterial methanotrophs, distantly related to
<i>Methylocaldum-Metylococcus</i> genera, and the presence of the newly
discovered acido-thermophilic Verrucomicrobia methanotrophs.
Alphaproteobacteria of the genus <i>Methylocystis</i> 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 CH<sub>4</sub> h<sup>−1</sup> mL<sup>−1</sup> 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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| ISSN: | 1726-4170 1726-4189 |