Efficiency of resource utilization may be key to the survival of heterotrophic microbes in frozen environments over thousands to millions of years. While little is known about how low temperatures affect resource efficiency in psychrophiles, study of the proteome of Methanococcoides burtonii suggested that efficient carbon utilization occurs during growth at low temperatures (Goodchild et al. 2004). Genome sequence analysis reveals that P. arcticus 273-4 can conserve resources via the glyoxylate shunt, a bypass of the TCA cycle which allows cells to conserve carbon when growing on 2-carbon compounds, as both isocitrate lyase and malate dehydrogenase are present. In addition, the transcriptome of P. arcticus 273-4 indicates that resource conservation occurs during growth at low temperatures even under nutrient-replete conditions (e.g., 20 mM acetate, 5 mM ammonium, and 1 mM phosphate). P. arcticus 273-4 increases the expression of 12 peptidases and five ribonucleases that probably enhance the recycling of nucleotides and amino acids over long generation times during growth at low temperatures. The ability to recycle the basic building blocks of cellular machinery at subzero temperatures is likely essential to long-term viability in permafrost.
Decreased energy metabolism at low temperatures was also a major aspect of gene expression during growth at low temperatures. The most pronounced decreases in P. arcticus 273-4 transcript abundance at subzero temperatures were in energy metabolism genes. These genes included ATP synthase, NADH dehydrogenase and TCA cycle genes. While it is generally thought that energy cost per generation is much higher at low temperatures than at optimal growth temperatures, instantaneous resource demands should be much lower at subzero temperatures. The energy needs of P. arcticus 273-4 at subzero temperatures appear to be met by low levels of expression of energy metabolism genes, suggesting that P. arcticus 273-4 is well adapted for heterotrophic metabolism in the permafrost.
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