The Qualitative and Quantitative Effects of Food on the Growth of A Soil Amoeba (Hartmanella Hyalina)

Abstract

ABSTRACT Among the free-living protozoa, excluding those forms which contain chlorophyll, two types of nutrition are found, holozoic and saprozoic; in the soil commonwealth there is an ample food supply for the saprozoic forms without reference to the other members of the micro-organic population, but the holozoic species present a different problem, since in the great majority of cases their food consists of the bacteria or other smaller organisms which occur with them in the soil solution. The idea that a normally holozoic animal might be induced to become saprozoic arose with the introduction of a suitable pure-culture technique. Among the earlier workers Beijerinck (1896), Frosch (1897) and Tsujitani (1898) all obtained “pure mixed cultures” of amoebae, and record their failure to grow these except in the presence of bacteria or yeasts, though Tsujitani was able to grow his amoebae with bacteria killed by heating them to 65 ° or 70 ° C. ; later Mouton (1902) records that an amoeba, a form obtained from soil, would not grow except in the presence of living bacteria, and Oehler (1916, 1924), who has perhaps worked more in this field than any other observer, has experienced great difficulty in obtaining any protozoan growth in cultures which do not contain bacteria or yeasts, either dead or alive, though successful growth was obtained in the case of Colpoda by feeding the culture with ground-up fish or powdered egg albumen. It further appears from Oehler’s work that, while the holozoic ciliates and flagellates are practically omnivorous provided that the food is supplied to them alive and of a suitable size, the amoebae tend to be very much more fastidious in their acceptance of food. All these writers seem to have been impressed by the enormous amount of bacterial food that a successful culture of protozoa can consume, and a quantitative study of this problem by Cutler and Crump (1924) showed that in the case of Colpidium colpoda in pure mixed culture the reproductive rate varied from 0·0 to 5·3 in 24 hours according as the number of bacteria per individual ciliate varied from 250 to 1,024,000; similar results have been obtained by Vieweger (1923)1, (1924).