Temperature dependence of metabolic rates for microbial growth, maintenance, and survival

TLDR

Prokaryotic communities survive with little nutrient in ice and permafrost, raising implications for microbial life on Mars and Europa. The study compares the temperature dependence of metabolic rates across microbial communities in permafrost, ice, snow, clouds, oceans, lakes, marine and freshwater sediments, and subsurface aquifer sediments. The authors categorize per‑cell metabolic rates into growth (microg(T)), maintenance (microm(T)), and survival (micros(T)) rates, with micros(T) for DNA and protein repair matching spontaneous damage rates. The growth, maintenance, and survival rates share a single activation energy (~110 kJ) and scale 10^6:10^3:1, show no minimum temperature, yield ~10 carbon turnovers per billion years at –40 °C, match rates in water, soil, and sediment at the same temperature, and indicate that micros(T) repair equals spontaneous damage, supporting liquid water availability below freezing.

Abstract

Our work was motivated by discoveries of prokaryotic communities that survive with little nutrient in ice and permafrost, with implications for past or present microbial life in Martian permafrost and Europan ice. We compared the temperature dependence of metabolic rates of microbial communities in permafrost, ice, snow, clouds, oceans, lakes, marine and freshwater sediments, and subsurface aquifer sediments. Metabolic rates per cell fall into three groupings: (i) a rate, microg(T), for growth, measured in the laboratory at in situ temperatures with minimal disturbance of the medium; (ii) a rate, microm(T), sufficient for maintenance of functions but for a nutrient level too low for growth; and (iii) a rate, micros(T), for survival of communities imprisoned in deep glacial ice, subsurface sediment, or ocean sediment, in which they can repair macromolecular damage but are probably largely dormant. The three groups have metabolic rates consistent with a single activation energy of approximately 110 kJ and that scale as microg(T):microm(T):micros(T) approximately 10(6):10(3):1. There is no evidence of a minimum temperature for metabolism. The rate at -40 degrees C in ice corresponds to approximately 10 turnovers of cellular carbon per billion years. Microbes in ice and permafrost have metabolic rates similar to those in water, soil, and sediment at the same temperature. This finding supports the view that, far below the freezing point, liquid water inside ice and permafrost is available for metabolism. The rate micros(T) for repairing molecular damage by means of DNA-repair enzymes and protein-repair enzymes such as methyltransferase is found to be comparable to the rate of spontaneous molecular damage.