The permafrost samples were obtained by slow rotary drilling without the use of any drilling solutions between 1991 and 1999. Evaluation of the aseptic sampling methods and contamination controls was done (Khlebnikova et al. 1990; Juck et al. 2005). The surface of extracted frozen core was trimmed away with a sterile knife, then immediately divided into sections of 5 cm long, placed in presterilized aluminum tins, sealed, and placed in frozen storage. All samples remained frozen throughout this process and during transport. In the laboratory, frozen samples were fractured in a class II positive-flow hood with a sterile knife, and only sections internal to the core were taken for microbiological analysis using sterile forceps (Shi et al. 1997; Rivkina et al. 1998).
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