Physiological response to temperature changes of the marine, sulfate-reducing bacterium Desulfobacterium...

The physiological response of bacteria to temperature is critical for the regulation of biogeochemical processes on daily, seasonal, and inter-annual time scales. We investigated the temperature response of the marine sulfate-reducing bacterium Desulfobacterium autotrophicum strain HRM2. Growth experiments in a temperature gradient block demonstrated that D. autotrophicum is psychrotolerant and grows between 0 and 31 degrees C. The normal range of temperature for growth is between 4 and 29 degrees C. The physiological response to temperature changes was studied with three sets of cells that were acclimated at 4, 10, and 28 degrees C, respectively. Sulfate reduction rates were determined in the temperature gradient block with short-term incubations to minimize growth. The rates were similar at the 4 and 10 degrees C acclimation temperature, and exhibited an enhanced response at 28 degrees C. At every acclimation temperature, sulfate reduction rates increased 20-fold from -1.7 to 41 degrees C. The relative proportion of cellular unsaturated fatty acids (e.g. cis16:1) and short-chain fatty acids increased when cells were grown at 4 degrees C compared to 28 degrees C. The proteome of D. autotrophicum strain HRM2 was studied by two-dimensional gel electrophoresis with soluble extracts of cells grown at the three respective acclimation temperatures. Protein patterns were similar with the exception of two proteins showing 5-10-fold lower abundance in the 4 degrees C culture compared to the 28 degrees C culture. In general, D. autotrophicum strain HRM2 responded to low temperatures by reduced metabolic activity rather than by pronounced de novo synthesis of specifically adapted enzymes. Such a strategy agrees well with in situ activities measured in field studies and may reflect a common physiological principle of psychrotolerant marine sulfate-reducing bacteria.