Bacterial genome replication at subzero temperatures in permafrost

Abstract

Microbial metabolic activity occurs at subzero temperatures in permafrost, an environment representing B25% of the global soil organic matter. Although much of the observed subzero microbial activity may be due to basal metabolism or macromolecular repair, there is also ample evidence for cellular growth. Unfortunately, most metabolic measurements or culture-based laboratory experiments cannot elucidate the specific microorganisms responsible for metabolic activities in native permafrost, nor, can bulk approaches determine whether different members of the microbial community modulate their responses as a function of changing subzero temperatures. Here, we report on the use of stable isotope probing with 13 C-acetate to demonstrate bacterial genome replication in Alaskan permafrost at temperatures of 0 to À 20 1C. We found that the majority (80%) of operational taxonomic units detected in permafrost microcosms were active and could synthesize 13 C-labeled DNA when supplemented with 13 C-acetate at temperatures of 0 to À 20 1C during a 6-month incubation. The data indicated that some members of the bacterial community were active across all of the experimental temperatures, whereas many others only synthesized DNA within a narrow subzero temperature range. Phylogenetic analysis of 13 C-labeled 16S rRNA genes revealed that the subzero active bacteria were members of the Acidobacteria, Actinobacteria, Chloroflexi, Gemmatimonadetes and Proteobacteria phyla and were distantly related to currently cultivated psychrophiles. These results imply that small subzero temperature changes may lead to changes in the active microbial community, which could have consequences for biogeochemical cycling in permanently frozen systems.

Microbial Metabolism in Soil at Subzero Temperatures: Adaptation Mechanisms Revealed by Position-Specific 13C Labeling

“…In a recent study, 13 C incorporation into microbial DNA was not detected after 1 month at subzero temperatures (Tuorto et al, 2014). This suggests that glucose utilization by microorganisms at -5°C were mainly intracellular metabolic responses to freezing and was rapidly activated.…”

Crenarchaeal heterotrophy in salt marsh sediments

“…Another possibility is that minor TRFs in the 13 C-carrier band are having their signal suppressed by the dominant TRF in the high concentration SIP experiment. Although our fingerprinting methods are highly reproducible (McGuinness et al, 2006;Tuorto et al, 2013), there is a suppression of smaller peaks in the TRFLP profile when screening clone libraries (Babcock et al, 2007) or samples where one microorganism is 410% of the community. This same mechanism may be inhibiting the detection of other active crenarchaea that are not synthesizing large amounts of DNA in our SIP incubations.…”

A New Analysis of Mars “Special Regions”: Findings of the Second MEPAG Special Regions Science Analysis Group (SR-SAG2)

“…These studies measured different aspects of metabolism such as DNA synthesis, respiration of acetate, or fluorescence of chlorophyll a in both pure culture and microcosm studies of organisms from soils, permafrost, and glacial ice from the Arctic and Antarctica (Table 2). One study of note examined genome replication within permafrost microcosms at -20°C that is highly suggestive of cell division (Tuorto et al, 2014). Another study worthy of notice demonstrated ammonia oxidation activity at -32°C that was sustained over 300 days, the length of the experiment (Miteva et al, 2007).…”