Microbial dynamics in a thawing world: Microbial ecology of a permafrost active layer

Abstract

Microbial assemblages in the active layer of thawing permafrost were investigated over two years across a spatially related thaw gradient. This is the first massive pyrosequencing project to investigate, document and compare the microbial community of such systems. In situ measurements of geochemical parameters enabled linkage of the community dynamics to significant shifts in C (carbon) balance and community structure. The study investigated communities from a palsa mire with three internal sites selected that were Increased thawing of permafrost, a significant global C sink, makes cryo-sequestered C available for microbial degradation. Methanogenic Archaea convert this C to the potent greenhouse gas methane. The discovery of a novel methanogen of the RCII archaeal lineage at up to 70% abundance of the community allowed recovery of a population genome. The environmentally recovered genome and proteome of this archaea, iii 'Candidatus Methanoflorens stordalenmirensis', indicates that hydrogenotrophic methanogenesis is its main energy conservation pathway. Enrichment of C storage and membrane associated genes support 'Ca. M. stordalenmirensis' genomic adaption to its active layer environment. Meta-analysis of community surveys, 16S rRNA and mcrA genes, suggested that 'Methanoflorens spp.' are dominant and ubiquitous methanogens in permafrost and peatland soils. This lineage had previously been identified as significant in temperate peatlands but was thought to be a negligible contributor to methanogenesis at high latitudes.iv