The Relation Between the Numbers of a Soil Bacterium and the Ammonia Produced by It in Peptone Solutions; With Some Reference to the Effect on This Process of the Presence of Amoebae

SUMMARY. Two sets of experiments on ammonia production from peptone were carried out, one with “YB” bacteria in liquid cultures, and another comparing “YB” and Hartmanella with “YB” alone in sand cultures. In liquid cultures an inverse linear relation was found to hold between bacterial numbers and efficiency. The greatest rate of production of ammonia was found to correspond to a bacterial content of about 500 million per c.c, any increase in bacterial numbers above this lowered the rate of ammonia production. The effect of diluting the inoculum ten times was to increase the “lag” period, both for bacterial growth and for ammonia production, to a week or more; after this extended “lag” period the cultures then followed a normal course. In sand cultures the presence of amoebae, while lowering the bacterial numbers, appears to increase the rate of ammonia production. It is suggested that the amoebae reduce the bacterial numbers from too high a valua to a value nearer the optimum for ammonia production, and so increase the rate of ammonia production. I should like to express my thanks to Mr Woolf, of the Sir William Dunn Institute of Biochemistry, Cambridge, for demonstrating the details of his method to me, and also to Dr Wishart and Dr Fisher, of the Statistical Department, Rothamsted, for help in the analysis of the results, and especially to Mr D. Ward Cuder, in whose department the work recorded in this paper was carried out, for his constant help and encouragement.