Analysis of the Sulfate-Reducing Bacterial and Methanogenic Archaeal Populations in Contrasting Antarctic Sediments

Abstract

The distribution and activity of communities of sulfate-reducing bacteria (SRB) and methanogenic archaea in two contrasting Antarctic sediments were investigated. Methanogenesis dominated in freshwater Lake Heywood, while sulfate reduction dominated in marine Shallow Bay. Slurry experiments indicated that 90% of the methanogenesis in Lake Heywood was acetoclastic. This finding was supported by the limited diversity of clones detected in a Lake Heywood archaeal clone library, in which most clones were closely related to the obligate acetate-utilizing Methanosaeta concilii. The Shallow Bay archaeal clone library contained clones related to the C 1 -utilizing Methanolobus and Methanococcoides and the H 2 -utilizing Methanogenium. Oligonucleotide probing of RNA extracted directly from sediment indicated that archaea represented 34% of the total prokaryotic signal in Lake Heywood and that Methanosaeta was a major component (13.2%) of this signal. Archaea represented only 0.2% of the total prokaryotic signal in RNA extracted from Shallow Bay sediments. In the Shallow Bay bacterial clone library, 10.3% of the clones were SRB-like, related to Desulfotalea/Desulforhopalus, Desulfofaba, Desulfosarcina, and Desulfobacter as well as to the sulfur and metal oxidizers comprising the Desulfuromonas cluster. Oligonucleotide probes for specific SRB clusters indicated that SRB represented 14.7% of the total prokaryotic signal, with Desulfotalea/Desulforhopalus being the dominant SRB group (10.7% of the total prokaryotic signal) in the Shallow Bay sediments; these results support previous results obtained for Arctic sediments. Methanosaeta and Desulfotalea/Desulforhopalus appear to be important in Lake Heywood and Shallow Bay, respectively, and may be globally important in permanently low-temperature sediments.Investigating the ecology of bacteria and archaea is vital to understanding the functioning of global biogeochemical cycles. Key questions include the identity of dominant members of microbial communities and the determination of their different roles. Sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) are important terminal oxidizers in the anaerobic mineralization of organic matter and can be seen as ecological equivalents, mineralizing organic matter to CO 2 or to CO 2 and CH 4 in, respectively, high-sulfate and low-sulfate environments (70). SRB are thought to outcompete MA when sulfate is freely available (e.g., in marine sediments), as cultured strains have higher specific affinities for the main substrates, acetate and H 2 , used by both groups (4, 30, 33). However, even in marine sediments, methanogenesis still occurs, primarily via C 1 compounds, such as methylamines, which SRB cannot use (69). In freshwater environments, where available sulfate is usually limited, sulfate reduction does still occur, but methanogenesis dominates (34, 64). Sulfate reduction accounts for up to 50% of organic matter degradation in coastal marine sediments, and similar proportions have been shown for methanogenesis in freshwa...

Some like it cold: microbial transformations of mercury in polar regions

“…Therefore, the involvement of SRB in methylation in polar regions, especially in anoxic sediments of coastal environments, where sulfate reduction is likely the dominant respiratory pathway, remains to be examined. This involvement is supported by observations that SRB are abundant in Arctic coastal marine sediments such as in Svalbard, Norway (Ravenschlag et al 2001), and in Antarctic sediments (Purdy et al 2003) and that psychrophilic SRB isolated from the same sediments actively reduced sulfate at in situ temperatures (Knoblauch et al 1999;Bruchert et al 2001). To the best of our knowledge, the role of FeRB in methylation in polar regions has not been explored though iron, like sulfate, reduction readily occurs in cold environments (Finke et al 2007).…”

Temporal evolution of methane cycling and phylogenetic diversity of archaea in sediments from a deep-sea whale-fall in Monterey Canyon, California

“…Despite this limitation, a few species of Methanogenium have been observed and even isolated from psychrophilic sulfate-rich marine sediments (Parkes et al, 1990;Franzmann and Liu, 1997;Chong et al, 2002;Purdy et al, 2003;Kendall and Boone, 2006). High abundance of the methylcoenzyme M reductase (mcrA) gene was documented in Methanogenium-dominated sediments in this study, suggesting that despite low temperatures, methanogenic activity belonging to H 2 -utilizing methanogens may occur in sediments underlying the whale-fall.…”

“…Archaea generally only represent 1-12% of the total marine and freshwater microbial diversity; however, in some environments, such as Antarctic sediments, they can comprise up to 34% of the prokaryotic community (Falz et al, 1999;Purdy et al, 2003). Under the whale-fall, these archaea appear to be comprised predominantly of methanogenic members of the Methanomicrobiales (Methanogenium) and Methanosarcinales (Methanosarcina and Methanococcoides), including phylotypes related to those found in other marine environments (Chong et al, 2002;Singh et al, 2005).…”

Desulfuromonas svalbardensis sp. nov. and Desulfuromusa ferrireducens sp. nov., psychrophilic, Fe(III)-reducing bacteria isolated from Arctic sediments, Svalbard

“…The in situ abundance of members of the family Geobacteraceae had been demonstrated for temperate as well as permanently cold marine sediments of the Arctic and Antarctica, as several sequences closely related to strains of the Geobacteraceae had been found in 16S rRNA clone libraries of these sediments (Ravenschlag et al, 1999;Bowman & McCuaig, 2003;Purdy et al, 2003;Mußmann et al, 2005). The isolation of strains 102 T and 112 T from marine sediments from Svalbard suggests that this group of bacteria is present in diverse freshwater and marine environments.…”