The presence of Ca (concentration, ca. 0.4 mM) in the growth medium causes cells of Desulfovibrio vulgaris (Hildenborough) to aggregate, leading to a decrease in plating efficiency. When the Ca concentration in the medium was reduced 20-fold, cell aggregation did not occur and the plating efficiency increased from an initial value of 34% to a final value of 56%.

A procedure for plating Sulfolobus acidocaldarius using Gelrite as the gelling agent is presented. The technique uses a supporting gel of 0.8% (wt/vol) Gelrite and an overlay soft gel of 0.4% (wt/vol) Gelrite, in which the colonies are grown. The plating efficiency was essentially 100%.