Extremophiles

, Volume 12, Issue 4, pp 481–490 | Cite as

Metabolic activity of Siberian permafrost isolates, Psychrobacter arcticus and Exiguobacterium sibiricum, at low water activities

  • Monica A. Ponder
  • Michael F. Thomashow
  • James M. Tiedje
Original Paper

Abstract

The Siberian permafrost is an extreme, yet stable environment due to its continuously frozen state. Microbes maintain membrane potential and respiratory activity at average temperatures of −10 to −12°C that concentrate solutes to an a w = 0.90 (5 osm), The isolation of viable Psychrobacter arcticus sp. 273-4 and Exiguobacterium sibiricum sp. 255-15 from ancient permafrost suggests that these bacteria have maintained some level of metabolic activity for thousands of years. Permafrost water activity was simulated using ½ TSB + 2.79 m NaCl (5 osm) at and cells were held at 22 and 4°C. Many cells reduced cyano-tetrazolium chloride (CTC) indicating functioning electron transport systems. Increased membrane permeability was not responsible for this lack of electron transport, as more cells were determined to be intact by LIVE/DEAD staining than were reducing CTC. Low rates of aerobic respiration were determined by the slope of the reduced resazurin line for P. arcticus, and E. sibiricum. Tritiated leucine was incorporated into new proteins at rates indicating basal level metabolism. The continued membrane potential, electron transport and aerobic respiration, coupled with incorporation of radio-labeled leucine into cell material when incubated in high osmolarity media, show that some of the population is metabolically active under simulated in situ conditions.

Keywords

Psychrobacter Siberian permafrost Exiguobacterium Salt tolerance Low temperature Low water activity 

Notes

Acknowledgments

This research was funded by the National Astrobiology Institute of NASA. We thank Tatiana Vishnivetskaya for input based on preliminary physiological data which allowed us to focus on a narrower number of interesting permafrost isolated strains for further studies within our laboratory. We acknowledge the assistance of Chia-Kai Chang, Gisel Rodriguez, and Matt Campbell. We thank Richard Lenski and Corien Bakermans for strains E.coli 606 and P. cryohalolentis, respectively.

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Copyright information

© Springer 2008

Authors and Affiliations

  • Monica A. Ponder
    • 1
    • 4
    • 5
  • Michael F. Thomashow
    • 1
    • 2
    • 3
    • 4
  • James M. Tiedje
    • 1
    • 2
    • 4
  1. 1.Department of Microbiology and Molecular GeneticsMichigan State UniversityEast LansingUSA
  2. 2.Department of Crop and Soil SciencesMichigan State UniversityEast LansingUSA
  3. 3.MSU-DOE Plant Research LabMichigan State UniversityEast LansingUSA
  4. 4.NASA Astrobiology Institute’s Center for Genomic and Evolutionary Studies on Microbial Life at Low TemperaturesMichigan State UniversityEast LansingUSA
  5. 5.101 Food Science and Technology (0418), Department of Food Science and TechnologyVirginia Polytechnic Institute and State UniversityBlacksburgUSA

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