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

Abstract

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.