Effects of cations on Methanosarcina thermophila TM-1 growing on moderate concentrations of acetate: production of single cells

Summary The effects of different concentrations of Mg²⁺, Ca²⁺, or Na⁺ on the morphology and growth of Methanosarcina thermophila TM-1 growing on acetate at concentrations comparable with those found in anaerobic digestors was studied. At 30 mm Mg²⁺ or less, M. thermophila grew as large aggregates that settled rapidly. At 100 mm Mg²⁺ or more, the bacteria grew as single cells or a mixture of single cells and small aggregates is suspended culture. Mg²⁺ was necessary for growth and could not be substituted by addition of either Ca²⁺ or Na⁺. The optimal Mg²⁺ concentration was 30 mm and no growth was observed at 400 mm Mg²⁺. Cultures could be adapted to 300 mm Mg²⁺ without a change in growth rate. Added Ca²⁺ was not required for growth and had no effect on cell morphology. Inhibition by Na⁺ was directly related to the Mg²⁺ concentration. When the Mg²⁺ was 0.05 mm or less, 0.35 m Na⁺ completely inhibited growth. However, more Na⁺ was required for inhibition at higher Mg²⁺ concentrations. The same inhibitory effect of Na⁺ was observed when the temperature was 52°C or 45°C. The potential for disaggregation of Methanosarcina aggregates in anaerobic digestor environments was discussed.Offprint requests to: B. K. Ahring