Metabolic activity of Siberian permafrost isolates, Psychrobacter arcticus and Exiguobacterium sibiricum, at low water activities
- 303 Downloads
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.
KeywordsPsychrobacter Siberian permafrost Exiguobacterium Salt tolerance Low temperature Low water activity
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.
- Friedmann EI (1994) Permafrost as microbial habitat. Viable microorganisms in permafrost. D. Gilichinsky. Puschinio, Russian Academy of Sciences, pp 21–26Google Scholar
- Gilichinsky D (1993) Viable microorganisms in permafrost: the spectrum of possible applications to investigations in science for cold regions. Fourth International symposium on thermal engineering and science for cold regions, Hanover, NH, US. Army Corp of EngineersGoogle Scholar
- Gilichinsky DA, Wilson GS, Friedmann EI, McKay CP, Sletten RS, Rivkina EM, Vishnivetskaya TA, Erokhina LG, Ivanushkina NE, Kochkina GA, Shcherbakova VA, Soina VS, Spirina EV, Vorobyova EA, Fyodorov-Davydov DG, Hallet B, Ozerskaya SM, Sorokovikov VA, Laurinavichyus KS, Shatilovich AV, Chanton JP, Ostroumov VE, Tiedje JM (2007) Microbial populations in Antarctic permafrost: biodiversity, state, age, and implication for astrobiology. Astrobiology 7:275–311PubMedCrossRefGoogle Scholar
- Ostroumov VE, Siegert C (1996) Exobiological aspects of mass transfer in microzones of permafrost deposits. Life Sci Space Mars Recent Results 18:79–86Google Scholar
- Pewe T (1995) Permafrost. Encylopedia Britannica, pp 752–759Google Scholar
- Ponder M (2005) Characterization of physiological and transcriptome changes in the ancient Siberian permafrost bacterium Psychrobacter arcticus 273-4 with low temperature and increased osmotica. Microbiology and molecular genetics. Michigan State University, East Lansing, p 215Google Scholar
- Rand RP (2004) “Osmotic Stress Pressure Measurements.” Retrieved 11-6-07, 2007, from http://www.brocku.ca/researchers/peter_rand/osmotic/osfile.html