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Correlates of viral and bacterial abundances in siberian and antarctic permafrost McLearn, Nicole


Despite the widespread occurrence and high abundance of bacteria and viruses in many environments, little work has been published to date on the abundances of viruses and bacteria in permafrost. Therefore, factors that affect viral and bacterial abundances in permafrost are still largely unknown. Permafrost samples from the Kolyma-lndigirka Lowland region of Siberia (70°N, 158°E), and the Beacon Dry Valley in Antarctica (77°S, 160°E) were examined for viruses. Soil type ranged from sands containing little carbon, nitrogen, and ice, to loams containing large quantities of carbon, nitrogen, and ice. Methodology for optimal virus recovery included testing of various eluants and filter testing. Sodium pyrophosphate was the best eluant (1.34x108 viruses g⁻¹ dry weight) over phosphate-buffered saline (8.09x107 viruses g⁻¹ dry weight) and virus-free water (2.46x106 viruses g⁻¹ dry weight). A glass fiber filter and 0.45 um polyvinylidene fluoride filter was the best combination (3.32x108 viruses g⁻¹ dry weight) over no filtering at all (too much detritus to count viruses), a 0.40 urn polycarbonate filter (2.30x107 viruses g⁻¹ dry weight), or a 0.45 μm nitrocellulose filter (3.10x107 viruses g⁻¹ dry weight). Sonication did not aid in virus recovery from permafrost (2.59x108 viruses g⁻¹ dry weight, no sonication; vs. 2.49x108- 2.70x108 viruses g⁻¹ dry weight, 10 - 300 seconds, 25 Watts sonication). Viral and bacterial presence was determined by epifluorescence microscopy; viral abundances ranged from 2.83x104 to 3.32x108 viruses g⁻¹ (dry weight); bacterial abundances ranged from 1.02x103 to 4.09x108 bacteria g⁻¹ (dry weight). Physical and chemical characteristics of permafrost were compared with viral and bacterial abundances. Permafrost type was associated with viral abundance, with loamy soils giving the highest abundances (~10⁸ viruses g⁻¹ dry weight) and sands giving the lowest abundances (ranging from below the detection limit of 2.83x10⁴ to ~10⁶ viruses g⁻¹ dry weight). Viral abundance was also associated with higher carbon, nitrogen, and ice contents, and a lower pH. This is consistent with other research into bacterial abundances in permafrost, which have shown that loamy soils have higher abundances, and sands have much less abundances, usually due to the scarcity of water and organic matter available.

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