Biosynthesis of methionine in an ethionine-resistant strain ofCandida utilis

The strainCandida utilis T 20 adapted to a high concentration of ethionine, excretes considerable amounts of methionine in a synthetic medium, about 40 times as much as the original non-adapted strain. At the same time, the amount of methionine in yeast cells incrncreased, predominantly in the pool (9 times as much as in the control). This ability to produce greater amounts of methionine in the pool or to excrete it into the medium is not permanent, since after 5 passages on agar with ut ethionine the amount of methionine was practically not increased as compared with the original non-adapted strain. An increase in free methionine and of methionine excreted into the medium was found on cultivating the strain in a molasses-containing medium, too.     

Toxic effects of fatty acids on yeast cells: dependence of inhibitory effects on fatty acid concentration.

The yeasts Saccharomyces cerevisiae, Candida utilis, and Candida lipolytica were used to investigate the action of different concentrations of fatty acids (from acetic to myristic acid) on cell growth, division, uptake of inorganic phosphate, and substrate oxidation. The former two yeasts were found to undergo an inhibition of growth, cell division, and phosphate uptake at lower acid concentrations and to experience the inhibition of substrate oxidation at higher acid concentrations. The concentration dependence of the action of fatty acids can be classified into four categories: 1) subthreshold concentrations which do not inhibit growth and have either no effect on, or stimulate, oxygen consumption; 2) threshold concentrations which lower the rate of growth, cell division, and phosphate uptake but do not inhibit the oxidation of carbon substrate; 3) above-threshold concentrations which inhibit partially even substrate oxidation, and 4) microbicide concentrations. Candida lipolytica displays the same sensitivity toward the action of fatty acids as the above yeast species; however, the threshold concentrations are higher and can be quickly lowered owing to oxidation by the yeast. The concentrations of fatty acids found in the medium after cultivations of yeast with n-alkanes are of the same order as limiting concentrations; the formation of acids with twelve and less carbons in the molecule can thus be assumed to be one of the basic reasons for lowering of biomass yields during cultivations on these hydrocarbons.     

Reversal of IAA-induced inhibition of flowering by aminoethoxyvinylglycine inChenopodium

Aminoethoxyvinylglycine (AVG) applied as a droplet (3 l, 0.1 mM) to the plumule of seedlings of both the short-day plantChenopodium rubrum and the long-day plantChenopodium murale counteracted to a great extent or even canceled the inhibition of flowering due to exogenous indole-3-acetic acid (IAA). This effect was more pronounced with the two substances administered simultaneously than with later application of AVG alone. AVG by itself in some cases promoted the percentage of flowering in bothChenopodium species. Application of IAA to the shoot apex was shown to elevate ethylene production in both species, whereas application of AVG alone was shown to suppress it. Thus, ethylene may be considered an active agent of flowering inhibition brought about by IAA application.     

Effect of changed cultivation conditions on the morphology ofAspergillus niger and on citric acid biosynthesis in laboratory cultivation

Cultivation ofAspergillus niger 97A in baffled flasks on a shaker brings about metabolic changes demonstrated in increased citric acid biosynthesis, morphological changes and alterations in the mycelial cell wall.     

Variability ofAspergillus niger after treatment withN-methyl-N′-nitro-N-nitrosoguanidine

N-Methyl-N'-nitro-N-nitrosoguanidine influences strongly the variability of Aspergillus niger MU 90, particularly on long-term treatment. The number of spores capable of growth decreases with the duration of treatment and the number of morphological and biochemical mutants considerably increases. The highest number of mutants with increased organic acid production was obtained after a mutagenic treatment when the number of surviving spores decreased below 1%.     

Growth and physiology of a yeast cultivated in batch and continuous culture systems

Inoculum size has been found to affect significantly the maximum attainable specific growth rate during batch cultivation ofCandida utilis. Lower inoculum size resulted in an increased growth rate and relatively longer lag. The culture is found to be most active in the beginning of the exponential phase as regards its RNA synthesis rate. Batch data were used for predicting the conditions of the yeast population in single-stage continuous culture system. Predicted and the experimental values showed a reasonable agreement. In single-stage chemostat the physiology of the yeast was studied on the basis RNA, DNA and protein synthesis rates at various growth rates. The results indicate that the productivity of cells and the rate of synthesis of macromolecules is highest at the dilution rate values of 0.33 to 0.35 hr⁻¹. In order to attain so-called unrestricted conditions of growth a pluristage pluristream continuous system was employed. It is assumed that under such conditions the specific growth rate and the synthetic activity of yeasts may reach its maximum on a given medium. The results presented do not show such conditions of growth under the experimental conditions employed (D ₁=0.35 hr⁻¹ andD ₂=0.2 to 1.7 hr⁻¹) withCandida utilis cultivated on beet molasses medium. Second stage of a two-stage two-stream continuous system is constantly fed with the cells from the foregoing stage; this category of cells on entering the new conditions of the second stage is expected to show some adaptation period. Experiments are reported to this effect.     

Effect of estradiol on the metabolism of testosterone by rat prostate

Prostatic tissue from normal, estradiol-treated, and castrated rats was incubated with testosterone, and the metabolites formed were studied. Pretreatment with estradiol-17β did not affect the total amount of testosterone metabolized per unit weight of tissue. In contrast, the total amount of testosterone metabolized was significantly reduced following castration. The formation of dihydrotestosterone (17β-hydroxy-5α-androstan-3-one; DHT) was not affected by treatment with estradiol, but was significantly reduced by previous castration. Estradiol treatment enhanced the formation of 17-keto metabolites of testosterone by the prostate, giving lower 17-hydroxy to 17-keto ratios than incubations with prostates from control or castrated rats. These results are consistent with the theory that the mechanisms leading to the involution of prostate after estradiol treatment and after castration are different.     

Relationship of sulphur metabolism and division ofChlorella pyrenoidosa cells

It was demonstrated that caproic acid inhibits the uptake of phosphate and sulphate byChlorella cells. These findings were used to demonstrate the existence of the previously hypothetical sulphur compound (Tamiyaet al. 1959–1961) essential to the process of division of the alga. A³⁵S-labelled substance was isolated by partition chromatography on a DEAE cellulose column; it was found to be thermolabile and capable of inducing division of the algae even in an inhibited culture. It was also demonstrated that the addition of the substance during the early hours of ontogenetic development shortened the latter by almost half. It can be concluded that the dark phase in the terminal stage of ontogenetic development has a positive effect on the synthesis of this S-substance.