Manipulations of AMP metabolic genes increase growth rate and cold tolerance in Escherichia coli: implications for psychrophilic evolution.

Diverse organisms have adapted to thrive at low temperatures (i.e., <20 °C, termed psychrophiles), colonizing the majority of earth's biosphere. In contrast with mesophiles (20-40 °C thermal range), all observed psychrophiles increase intracellular adenosine 5'-triphosphate concentrations as temperatures decline; this phenomenon has been described as an important compensatory mechanism to deal with decreases in thermal energy and molecular motion. We considered purine metabolic pathways in class gammaproteobacteria (n = 115) to investigate metabolic and evolutionary bases of this process. A survey of the KEGG database indicated that psychrophilic purine metabolic pathways tend to be enriched with de novo adenosine 5'-monophosphate (AMP) synthetic enzymes, whereas mesophiles tend to be enriched with AMP degradative enzymes. Function of the observed psychrophilic pathway structure was tested by engineering the mesophilic gammaproteobacterium Escherichia coli to reflect psychrophilic purine metabolism, specifically by expressing adenylosuccinate synthetase (purA) from the psychrophilic gammaproteobacterium, Psychrobacter cryohalolentis, in an AMP nucleosidase (amn)-deficient background. Modified E. coli was capable of growing up to ∼70% faster at low temperatures and became up to ∼10-fold more cold tolerant relative to wild type. These findings highlight potentially important transitional steps in psychrophilic evolution.