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%.     

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.     

Theory of semicontinuous and continuous cultivation applied to the yeastTorula utilis

Были выведены математические зависимости между скоростью разведения и скоростью роста в условиях полунепрерывной культивации микроорганизмов. Было доказано, что вполне непрерывный способ культивации представляет особыи—крайний—случай полунепрерывных процессов и позволяет обработку максимального количества субстрата на единицу времени и объема ферментора. При изучении оптимальных условий размножения дрожжей Torula utilis было экспериментально доказано, что непрерывный процесс представляет одновременно наиболее удобный способ осуществления ферментации, позволяющий полное использование субстрата и мощности оборудования. Было доказано, что в случаях, когда дрожжи используют один источник углерода или же различные истичники углерода одновременно и с одинаковой скоростью, одноступенчатый способ ферментации более выгоден, чем многоступенчатый процесс.     

Uptake of some cations byCandida utilis

The affinity of a number of bivalent and tervalent cations for the yeastCandida utilis was shown to decrease from Zn²⁺ to Ca²⁺. Ferric ions inhibited the uptake of Zn²⁺ but not vice versa. Inhibition of Zn²⁺ uptake in a synthetic medium with Fe³⁺ does not decrease the content of crude protein in cells.