Characterization of Permafrost Sediments

It is well established now that Earth permafrost from Arctic and Antarctic regions, the age of which is defined as the time of stay at subzero temperatures and can vary from several thousands up to a few million years, represents a unique opportunity to investigate ancient forms of life. Detection of considerable numbers of viable microorganisms in frozen Arctic and Antarctic sediments [Vorobyova et al., 1997, Soina &Vorobyova, 2004, Vishnivetskaya et al., 2000, 2006, Gilichinsky et al., 2007] allows studying of ancient bacterial communities in various aspects—from their age and period of preservation in permafrost and population diversity, to more special characteristics, including the origin and evolution of antibiotic resistance.

For isolation of ancient antibiotic resistance strains, we used permafrost samples of different ages and genesis (Table 1).

Arctic permafrost samples were collected at the Polar Regions of the Kolyma lowland, Coast of Laptev Sea and Coast of East-Siberian Sea. The region is characterized by the presence of a thick depth layer of polygonal ice (Fig 1).

Figure 1. Polygonal ice sheets on the cost of East-Siberian Sea

Antarctic permafrost samples were recovered from the Dry Valleys polar desert, which is the largest of the ice-free Antarctic regions. In earlier works it was shown that Dry Valley permafrost had several orders of magnitude lower number of viable cells and had less microbial diversity than arctic permafrost, but the spectrum of microorganisms isolated from Antarctic permafrost on the whole was similar to that of Arctic surface ecosystems and other cold habitats [Vorobyova et al., 2005, Gilichinsky et al., 2007].

The preparation of the samples for microbiological analysis was performed as described previously [Vishnivetskaya et al., 2000, 2006]. The sampling from permafrost cores, transportation and storage of the samples, control and specialized tests, have ensured that microorganisms recovered from permafrost samples were not contaminants but were indigenous to the samples [Vishnivetskaya et al., 2000, 2006, Gilichinsky et al., 2007].

Table 1. Characteristics of Arctic and Antarctic permafrost samples

Region of sampling

Borehole number

Age (YBP)*

Depth (m)

Bacterial cell counts, (CFU/g)**

Arctic region Coast of Laptev Sea

1/01-DAV

Late-Pleistocene-Ice-

Complex

15- 40 K

28.0

1.5x 102

03/03-Tiksi

2.0

1.0x 107

12/03-Tiksi

5.0

7.2x 106

3/01-DC

Middle-Pleistocene 220-390 K

22.5

6.0x 105

Arctic region Kolyma Lowland

Bank of river Grand Chukochia

Pleistocene

2-3 M

34.0

4.2x10 4

Bank of river Alazeya

15/91

Late Pliocene 3 M

28.0

3.2x104

Bank of river Homus-Yuryiah

11/89

Late Pliocene- Early

Pleistocene

2-3 M

24.0

6.8x103

25.5

1.4x103

Bank of river Homus-Yuryiah

Pleistocene

2-3 M

39.9

4.4x103

Bank of river Homus-Yuryiah

4/93

Middle-Pleistocene 200-220 K

4.0

8.7x103

Bank of river Homus-Yuryiah

3/93

Middle-Pleistocene 200-600 K

6.0

6.2x103

Shore of Grand Oler Lake

1/95

Holocene 3-5 K

1.75

4.8x104

8.75

7.8x104

Arctic region Coast of East-Siberian Sea

14/99

Late-Pleistocene-Ice-

Complex

15- 35K

13.6

2.0x106

14.6

5.0x105

Antarctitida Beacon Dry Valley

A99 6/99 6/99

4.85

2.3x104 4.1x103 5.2x102

K=103 years, M=106 years; The total number of viable microorganisms was determined after 3 days of incubation at 25°C on solid nutrient media by direct counting of colony forming units (CFU/g).

The number of platable cells in different Arctic and Antarctic samples ranged from 102 to 10' CFU/g (Table 1) and was comparable with earlier published data on permafrost sediments [Vorobyova et al., 1997; Vishnivetskaya et al., 2006]. The majority of the strains (70-80%) initially isolated from permafrost samples of different age were non spore-forming Gram-

positive bacteria. Spore-forming Gram-positive bacteria composed from 10 to 20% of all bacteria in the samples. Only 2-5% of isolated strains could be referred to Gram-negative bacteria.

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