Factors Affecting the Growth and Fat Formation of Rhodotorula gracilis

Abstract

Summary: The vitamin requirements of Rhodotorula gracilis are satisfied by inclusion in the growth medium of pantothenic acid and thiamine. For maximum growth in the particular medium and with the size of inoculum used in our experiments a concentration of about 10 μg of pantothenate/1 was sufficient but for rapid early growth a higher concentration was beneficial. Pantothenic acid can be replaced by β‐alanine but maximum growth response then occurs only in the presence of asparagine. Either ammonium sulphate or urea provides a suitable source of nitrogen for growth of the organism. Shake flask experiments with a synthetic medium showed that a solution containing only glucose and phosphate was adequate for fattening, that wide limits in pH value (e.g. 4–8) were permissible and that the rate and efficiency of fat production were not affected by large differences in the concentration of sugar. Provided sugar was still present in the medium a progressive decrease in the percentage of protein was accompanied by a corresponding increase in the percentage of fat in the yeast. When aeration was prolonged beyond the point at which all the sugar was exhausted, this trend was reversed. The fat produced during fattening had a lower iodine value than that produced during normal growth. Only a small proportion of the fat in Rh. gracilis is in the free condition and extractable by direct treatment with a simple solvent. Preliminary hydrolysis with hot HCl is necessary for quantitative release of the fat. Refinery cane molasses provides a suitable source of sugar both for growth and for fattening of Rh. gracilis. Growth in a fermentor with incremental feeding, under conditions of high aeration and rapid stirring, gave a yield of dry yeast equivalent to 52–54% of the sugar consumed; the doubling time during the logarithmic growth phase was 3 h. Aeration of Rh. gracilis in a phosphate‐molasses medium resulted in a rapid consumption of sugar during the whole period of aeration. This was accompanied by an increase in the weight of yeast, accounted for by an increase in all constituents—fat, carbohydrate, mineral matter and a small amount of protein formed from the residual nitrogen carried over from the growth medium. Since much more fat than protein was produced the percentage of fat in the yeast rose and the percentage of protein fell. The proportion of carbohydrate in the cell was subject to some fluctuation. Under certain conditions it appears that the reserves of carbohydrate may be drawn upon to provide energy for fat formation, resulting in an actual destruction of cellular carbohydrate. The proportion of sugar converted to fat rose to a maximum between c. 14–23 h and then rapidly declined. For a short period a fat coefficient of over 40% was attained in one experiment. Thereafter conversion was relatively inefficient, a small quantity of fat being produced from the consumption of a large quantity of sugar.

Enhanced lipid and biodiesel production from glucose‐fed activated sludge: Kinetics and microbial community analysis

“…As the pH in the culture was not controlled, sharp declines in the culture pH from 6.5 to around 2.5 were observed in all experiments conducted (Figure 2e). This phenomenon could have been caused by one or more of the following: endogenous production of organic acids by the activated sludge microorganisms;23 the release of acid in the culture with use of ammonium sulfate as the nitrogen source due to the preferential assimilation of NH radical;29 and the formation of carbonic acid due to the dissolution of the CO 2 produced by microorganisms into the culture 30. Although it was previously reported that culture pH values below 3 reduced biomass and lipid production in pure cultures of oleaginous yeasts31 and bacteria,32 the results of this study showed that lipid accumulation in activated sludge occurred even at these very low pH levels, suggesting that some members of wastewater microbial communities are capable of accumulating lipids at these extreme conditions.…”

Fatty Acids of Rhodotorula gracilis: Fat Production in Submerged Culture and the Particular Effect of pH Value

“…It is widely reported that nitrogen-limited growth conditions increase the ratio of lipid to cell dry weight and R. gracilis can be so induced to produce up to 60% of its own weight of fat, thus giving a fat coefficient (g of fat produced/100 g of glucose utilized) of 15.0-21.0 (Enebo, Anderson & Lundin, 1946;Lundin, 1950;Borrow et al, 1961;Allen, Barnard, Fleming & Hollis, 1964).…”

Conversion of cheese whey to yeast lipid and single cell protein

“…The final cell yields of 196 to 268 g/10 L are considerably higher than other reports of cell yields (3,54,63). The % fat dry wt.…”

“…In a few cases5 swabs of material were collected in sterile tubes. Sampling sites and the number of organisms isolated from each were: soil [3], rotting tree stump [2], soil edge of Lake LaVerne [3], horse manure [2], lawn soil [3], spoiled milk [1], standing water [1], and a drain of Iowa State University dairy plant [5]. After preliminary studies indicated that the university dairy plant furnished promising organisms, 42 isolates were obtained from two other cheese plants in Iowa.…”