No abstract

The yeast Candida utilis was continuously synchronized by the phasing technique (6 h doubling time) with either iron or nitrogen as the limiting nutrient. Iron limitations resulted in decreased molar growth yields with respect to the carbon substrates and ammonia and in increased specific rates of oxygen uptake. Relatively low energy-charge values were maintained by the iron-limited culture. All these taken together seemed to indicate that the growth of the yeast under iron limitation was also limited by metabolically available energy. Consideralbe amounts of ethyl acetate were produced by the yeast under phased cultivation when the growth was limited by iron but not by nitrogen. In vitro studies using cell-free extracts showed that the substrates for ethyl acetate synthesis were acetyl coenzyme A (acetyl CoA) and ethanol. Under iron-limited growth acetyl CoA seemed to be diverted to ethyl acetate formation rather than being oxidized through the tricarboxylic acid (TCA) cycle. The possibility of energy limitation under iron-limited growth being brought about by the reduced capacity of the yeast to oxidize acetyl CoA through the TCA cycle is considered.

Synthetic laboratory strains of two species of flour beetles, Tribolium castaneum and T. confusum, were compared in terms of the voracity of larvae for eggs. Significant differences were observed between the species. Tribolium castaneum was much more cannibalistic with the greatest difference observed in 4— to 14—days—old larvae. Older active larvae of both species ate more eggs than did younger larvae. No significant differences were observed in the choice of eggs of both species when they were offered at the same time, but slightly more T. castaneum eggs were consumed than T. confusum eggs when larvae were supplied eggs of a single species. In one experiment a control series was maintained in the same manner as the experimental series, except that the larvae were not given eggs. Fecundity of adult T. castaneum emerging from these larvae was lower than in adults from the experimental series which had fed on eggs during the larval stage. No such difference was observed between experimental and control groups in T. confusum. It is suggested that differences in egg cannibalism by larvae of the two species of flour beetles may account in part for the superiority of T. castaneum in competition with T. confusum under the given conditions (29°C, to to 70% R. H.).

A modified chemostat is described which may be used to maintain a continuously phased population in the culture for periods of many months. Preliminary results with Candida utilis show that changes in the amino acid pool occur over the cell cycle, and that these changes alter with growth rate. The significance of the method and its relationship to chemostat culture are outlined.

Total lipids were extracted from cells of Candida utilis grown in batch, chemostat, and phased culture. Thin-layer chromatography of the extracts showed qualitative changes in the different lipid classes with growth. Gas–liquid chromatography was used to follow quantitative changes in the fatty acid constituents. Changes were found to be analogous to those previously reported for the amino acid pool, i.e., characteristic of the medium, of growth rate, and of the environment. The significance of the changes, and of the methods used to detect them, are discussed in relation to the growth and metabolism of the cell and of the culture.