Diversity of Viable Bacteria and Archaea

The catalog of viable Bacteria recovered from permafrost and associated environments, currently includes at least 70 genera (Table 5.2). Cultured isolates recovered from permafrost are capable of a wide range of metabolic processes including aerobic and anaerobic heterotrophy, chemolithoautotrophy, sulfate-reduction, methanotrophy, methanogenesis (Gilichinsky et al. 1995; Steven et al. 2006) and even phototrophy (Chap. 6). Both Gram-positive and Gram-negative cells are represented, and spore-forming Bacteria are also commonly isolated, although the abundance of spore-forming Bacteria varies widely between geographically separated permafrost samples. For example, spore-forming genera dominated the culturable community from 2 to 9 m (69% and 100% of isolates, respectively) Canadian high Arctic permafrost samples (Steven et al. 2007a, 2008a), whereas spore-forming genera only composed 30, 5 and 1% of Siberian (Shi et al. 1997), Spitsbergen Island (Hansen et al. 2007) and Chinese alpine (Bai et al. 2006) permafrost isolates, respectively. Firmicutes and Actinobacteria generally represent a high proportion of the permafrost microbial community, accounting for up to 100% of Canadian high Arctic isolates (Steven et al. 2008a), 60% of Chinese alpine permafrost isolates (Bai et al. 2006) and 45% of Siberian permafrost isolates (Shi et al. 1997). To date, the phylogenetic groups that account for the anaerobic Bacteria community in permafrost remain poorly characterized.

Cryopegs are lenses of supercooled, saline liquid water within the permafrost (Bakermans et al. 2003) that can harbor substantial numbers of viable microbial cells (Table 5.1). These include a variety of anaerobic and aerobic, spore-less and spore-forming bacteria (Table 5.2), with a Psychrobacter-related isolate accounting for 53% of all isolates, suggesting this organism was a dominant community member (Bakermans et al. 2003).

A single report of the microbial community in an Alaskan permafrost ice wedge indicated relatively high numbers of viable microbial cells (Table 5.1), although the diversity of the recovered isolates was low (Katayama et al. 2007). The phylogenetic groups of the isolates were similar to those identified in permafrost soils (Table 5.2).

The description of viable Archaea in permafrost remains limited. Methanogenic Archaea, generally occur in low numbers (102-103 g-1) and not in all samples (Rivkina et al. 1998, 2002). Recovered isolates related to the genera Methanosarcina and Methanobacterium (Rivkina et al. 2007) and methanogenic activity detected in Siberian permafrost samples suggests that methanogenesis occurs at in situ permafrost temperatures (Rivkina et al. 2000, 2002). We recently detected halophilic Archaea in saline enrichment cultures from Canadian high Arctic permafrost, indicating that these organisms are members of a viable permafrost microbial community (unpublished data).

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