Biogeochemical activity of anaerobic microorganisms from buried permafrost sediments

Permafrost sediment samples, ranging in age from 7 thousand to 2 million years, from the northeastern region of Russian Arctic were analyzed for evidence of reducing conditions, viable populations of anaerobic bacteria and their metabolic endproducts. Field analyses of samples showed that all sediments were reduced with a redox potential ranging from +40 to -256 mV. Ferrous iron, acid-soluble sulfide, and methane were detected in the frozen sediments. Direct bacterial counts were! 10(7) to 10(8) cells/g sediments as determined by epifluorescence microscopy using acridine orange. Denitrifiers and (H-2 + CO2)-utilizing methanogens were detected in all samples, and acetoclastic methanogens, sulfate reducers, and Fe(III) reducers were detected in some samples and at much lower numbers. [S-35]Sulfide production from [S-35]sulfate was detected in soils incubated anaerobically at 4 degrees C for 6 months. Thus anaerobic metabolic activity was present at temperatures near freezing. These results suggest that viable anaerobic bacteria reside in aged, reduced permafrost sediments. Future investigation should focus on detecting activity in the frozen state.