The Effect of Colpidium on Ammonia Production by Soil Bacteria

SUMMARY Two series of experiments were performed with a mixed culture of two species of soil bacteria with and without Colpidia, one series on a solution of peptone in soil extract, the other on a synthetic medium containing alanine. An appreciable reduction in bacterial numbers was found on both media to occur in the Colpidium cultures as compared with the controls. On the peptone medium the Colpidium cultures produced slightly more ammonia than the controls, in spite of their lower numbers of bacteria. On the alanine medium the Colpidium cultures produced nearly the same amount of carbon dioxide and of ammonia as the controls. In both series of experiments an inverse linear relation was found to exist between bacterial numbers and efficiency of ammonia production, and the same was found for carbon dioxide production in the second series. The regression coefficients of efficiency on average bacterial numbers are significantly different in the Colpidium and control cultures fo the second series. It follows that the stimulating effect of the presence of Colpidia is not due solely to the reduction of bacterial numbers to an optimum value, and it is suggested that in the cultures in which Colpidia are present, the bacteria are kept in a state of youth for a longer period.