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Project Progress

Bacteria in the Siberian permafrost environment must contend with low temperatures (-10°C) and low water activity (a_w=0.85-0.9). To gain knowledge of microbial adaptation to low temperature and low water activity, the genome of a Siberian permafrost isolate, Psychrobacter arcticus 273-4, was sequenced and gene expression monitored using microarrays consisting of 70-mer oligonucleotides representing the large majority of predicted genes for this bacterium. Only a few genes known to be low temperature and salt responsive in certain mesophiles and psychrotrophs were differentially expressed in P. arcticus, although many were constitutively expressed. Experiments reveal that shifting P. arcticus from 22°C to 4°C resulted a 2-fold increase in transcripts for certain transport-associated and metabolic genes. Genes for increased synthesis and uptake of compatible solutes were up-regulated in the presence of high salinity (5% NaCl) which may help balance the cell’s internal osmolarity. Several genes with unknown functions were also up-regulated in response to low temperature and high salinity, which may indicate their importance in stress survival. Growth in 5% NaCl-amended 1/2 TSB lead to induction of capsule synthesis genes. A capsule was visible around cells grown at both 22°C and 4°C that could allow P. arcticus to adhere to soil particles within the permafrost. In addition, total respiratory activity increased in the presence of high salt (5% NaCl), perhaps due to increased expression of genes encoding a Na⁺-dependent dehydrogenase and a decarboxylase, suggesting that P. arcticus has adapted for energy generation in the low temperature and low water activity of the permafrost environment.