Growth Characteristics of Rhodotorula gracilis

Previous studies have shown that Rhodotorula gracilis is capable of forming large quantities of fat under suitable conditions (Enebo et al., 1946; Pan et al., 1949; Steinberg and Ordal, 1954a). It also has been demonstrated that growth and fat formation takes place in two distinct phases (Enebo et al., 1946). Steinberg and Ordal (1954a, 1954b) have studied the fattening phase in some detail; however, very little is known about the optimum conditions for growth of this organism. There is, in general, a lack of accurate published in formation on the effects of pH, temperature, and aeration on the growth of yeasts. Only a few studies have appeared in the literature describing the use of pH controlling equipment in fermentation studies (Finn et al., 1950; Kempe et al., 1950; Neish and Blackwood, 1951; Maxon and Johnson, 1953; Lakata, 1954; Steinberg and Ordal, 1954a; McKee, 1955). In most cases only the initial pH was adjusted and observed and, where temperature or other conditions were variable, generally no pH control was used. There are no temperature studies reported in the literature for R. gracilis. Enebo et al. (1946) used a temperature of 28 C for both growth and fat formation. Every known investigator since that time has used this temperature. Several investigators have made quantitative studies on the effect of aeration on yeast growth (Olson and Johnson, 1949; White and Munns, 1951b; Maxon and Johnson, 1953). The only study on the effect of aeration on R. gracilis was made by Pan et al. (1949) who investigated the effect of air flow rate on combined growth and fattening. An increase of air flow rate from 0.1 to 1 volume of air per minute had no effect on the efficiency of sugar utilization nor on fat content. No ineasure of the effective oxygen-absorption rate was given. Agarwala and Peterson (1950) and Chiao and Peterson (1953) reported on the efficiency of sugar utilization by R. gracilis. However, the medium used by these workers contained nonsugar carbon compounds which could be utilized by the organism, which makes any interpretation of their results equivocal. The object of this investigation was to determine the effect of pH and temperature on total amount and rate of growth of R. gracilis under conditions of controlled