Higher Temperature and Hydrogen Availability Stimulated the Methanogenic Activity in East Antarctic Subglacial Sediment

Abstract:

Subglacial ecosystem has been recognized as an environment with considerable methanogenic activity, and therefore is of significant impact on global methane budget and climate change. Although the methanogens have been discovered at a few subglacial environments, the methanogenic activity there is yet insufficiently studied, especially on the effects of environmental parameters, due to technical difficulties on sampling and cultivation. Here, in this study, we attempt to access the methanogenic activity and community structure in response to temperature and substrate availability.

An integrated approach including in vitro cultivation and molecular techniques were employed. A subglacial sediment from Larsemann Hills, East Antarctica was incubated at different temperatures (1, 4, 12 ^oC) supplied with H₂+CO₂ or sodium acetate to estimate the methanogenic activity. The McrA gene which is a specific marker for methanogens was amplified with primer ME and ML to construct phylogenetic trees. This functional gene was also quantified by Q-PCR before and after the incubation to estimate the increase of methanogens.

After 8 months a highest methanogenesis rate of 226 pmol/ day/ gram sediment was observed at 12 ^oC with H₂ supplying, which was 2 times higher than that with acetate supplying, clearly suggesting that H₂ is a preferable substrate than acetate. The methanogenesis rate without supplying extra substrate showed positive temperature dependence with rate of 23.3, 24.8, 131 pmol/day/gram sediment at 1 ^oC, 4 ^oC, and 12 ^oC, respectively. The McrA copy number was increased more than 300 times and 50 times with H₂ and acetate supplying respectively after the incubation. 94% and 67% of the mcrA gene sequences were classed into methanomicrobiales which were hydrogen-trophic methanogens in the two clone libraries with primer ML and ME respectively. This finding suggests the potential effect of methanogenesis under glacier on the climate change.