Isolation and characterization of bacteria from ancient siberian permafrost sediment.

De-Chao Zhang,Gennady Griva,Franz Schinner,Rosa Margesin,Anatoli Brouchkov

doi:10.3390/biology2010085

Abstract

In this study, we isolated and characterized bacterial strains from ancient (Neogene) permafrost sediment that was permanently frozen for 3.5 million years. The sampling site was located at Mammoth Mountain in the Aldan river valley in Central Yakutia in Eastern Siberia. Analysis of phospolipid fatty acids (PLFA) demonstrated the dominance of bacteria over fungi; the analysis of fatty acids specific for Gram-positive and Gram-negative bacteria revealed an approximately twofold higher amount of Gram-negative bacteria compared to Gram-positive bacteria. Direct microbial counts after natural permafrost enrichment showed the presence of (4.7 ± 1.5) × 108 cells g−1 sediment dry mass. Viable heterotrophic bacteria were found at 0 °C, 10 °C and 25 °C, but not at 37 °C. Spore-forming bacteria were not detected. Numbers of viable fungi were low and were only detected at 0 °C and 10 °C. Selected culturable bacterial isolates were identified as representatives of Arthrobacter phenanthrenivorans, Subtercola frigoramans and Glaciimonas immobilis. Representatives of each of these species were characterized with regard to their growth temperature range, their ability to grow on different media, to produce enzymes, to grow in the presence of NaCl, antibiotics, and heavy metals, and to degrade hydrocarbons. All strains could grow at −5 °C; the upper temperature limit for growth in liquid culture was 25 °C or 30 °C. Sensitivity to rich media, antibiotics, heavy metals, and salt increased when temperature decreased (20 °C > 10 °C > 1 °C). In spite of the ligninolytic activity of some strains, no biodegradation activity was detected.

Highlights

Permafrost is one of the most extreme environments on earth and covers more than 20% of the HDUWK¶V land surface; it has been defined as lithosphere material that is permanently exposed to temperatXUHV °C and remains frozen for at least two consecutive years, and can extend down to more than 1,500 m in the subsurface [1]
We investigated the culturable heterotrophic microbial population in ancient (Neogene) permafrost collected from one of the oldest permafrost areas on earth, located in Siberia and permanently frozen for 3.5 million years
A number of cold-adapted permafrost microorganisms are able to grow at subzero temperatures down to í10 °C [4,63,66,68]

Summary

Introduction

Permafrost is one of the most extreme environments on earth and covers more than 20% of the HDUWK¶V land surface; it has been defined as lithosphere material (soil, sediment or rock) that is permanently exposed to temperatXUHV °C and remains frozen for at least two consecutive years, and can extend down to more than 1,500 m in the subsurface [1]. Considerable abundance and diversity of microorganisms, including bacteria, archaea, phototrophic cyanobacteria and green algae, fungi and protozoa, are present in permafrost [4±6]. The characteristics of these microorganisms reflect the unique and extreme conditions of the permafrost environment. Permafrost soils may contain up to 20% or more unfrozen water in the form of salt solutions with a low water activity (aw = 0.8±0.85) [7] Microorganisms in this environment have to thrive under permanently frozen conditions, oligotrophic conditions, complete darkness, constant gamma radiation and extremely low rates of nutrient and metabolite transfer [4,5]. Substantial growth and metabolic activity (respiration and biosynthesis) of permafrost microorganisms at temperatures down to í20 °C and even í35 °C have been demonstrated [8±10]

Methods

Results

Discussion

Conclusion