The psychrophilic response to growth at cold temperatures: Functional genomics of the permafrost bacterium Psychrobacter arcticus 273-4.

摘要

Permafrost is an environment that imposes three selective pressures limiting the metabolism of resident microbes: low temperature, low water activity, and low nutrient availability. Furthermore, resident microbes are exposed to low continuous doses of background gamma-irradiation which should shear genomic DNA. In spite of these characteristics, microbes have been isolated from Siberian permafrost 2-3 million yr in age. The present work aims to elucidate the cold acclimation responses that permitted maintenance of viability over thousands of years in Psychrobacter arcticus 273-4, an isolate from Siberian permafrost. P. arcticus could have survived long term storage in the permafrost by inducing a dormant survival stage upon exposure to cold. I demonstrate that this is not the case. Rather survival of lethal stresses decreases with decreasing growth temperature. The transcriptome response to growth at 4°C, a cardinal temperature used in cold acclimation studies was narrow in the scope of genes differentially expressed. However, when P. arcticus was challenged with growth at subzero temperatures in a high salt defined medium, global expression decreased for genes involved in energy metabolism, anabolic metabolism, and the basal machinery of transcription and translation. Temperature compensation via gene expression was observed in expression for carbon and nitrogen incorporation, sulfur metabolism, biosynthesis of key amino acids and cell envelope dynamics. Changes in amino acid metabolism could be correlated to bias in amino acid content of genes highly expressed at subzero temperatures, suggesting that the observed changes have ecological relevance for P. arcticus in cryo-environment.