Effect of aeration and agitation on the biosynthetic activity of diffusely growing Aspergillus niger.

A considerable lowering of aeration demands occurs during diffuse growth of citric acid-producing Aspergillus niger in a submerged cultivation. However, the diffuse culture poses stricter demands on the type of aeration and agitation. The impeller frequency affects considerably the morphology of the producer fungus and the accumulation of citric acid. The effect of impeller frequency on the distribution of air in the medium and on the amount of air fed into the diffuse culture is less important.

Immunological changes after long-term feeding of germfree piglets with protein isolates and yeast cell walls from Candida utilis as food additives.

Germfree piglets were fed a diet supplemented with cell walls and a protein isolate from Candida utilis for 54 days. Besides morphological signs of activation of the lymphoid tissue which occurred primarily in the intestine of piglets which had been fed yeast cell walls, even an increased serum immunoglobulin level could be detected. In sera and intestinal content of piglets fed both with cell walls and isolated protein, specific antibodies capable of agglutinating yeasts were present. Even though a limited number of experimental animals was employed it can be concluded that the yeast material added to the diet elicited an immune response.

Comparison of growth rates of two clones of Bacillus subtilis, producer of alpha-amylase.

In a population of the productive Bacillus subtilis strain the production of alpha-amylase differentiates at the cell level. Individual cells in the population were analyzed and the production of isolates was tested. The mean specific activity of alpha-amylase in the productive group after the isolation was 5.0 U/mg dry substance and in the nonproductive group 1.5 U/mg dry substance. This ratio remained unchanged during long-term observations and after repeated transfers. In selected strains of both groups the specific growth rate was determined in a synthetic medium containing various amounts of casein hydrolyzate. The detected differences in the growth rate between the productive and the nonproductive clones are determined by amino acid concentration.

Production of extracellular enzymes in continuous culture.

The production of bacterial enzymes in batch fermentations is compared with results obtained in continuous culture. When studying the production of alpha-amylase in Bacillus subtilis it was found that instability of the enzyme synthesis was due to nonhomogeneity of the population rather than to "the culture's history" (i.e. succession of several physiological states necessary for the enzyme production). The plasmid contained in the production clone was found to be the factor responsible for the alpha-amylase production. Predominance of the production clone or of the nonproduction one depends on the cultivation conditions used. As compared with batch cultivation the continuous production yields higher enzyme concentrations under optimal conditions and the fermentor productivity may be four to five times higher.

Accumulation of 2-oxo acids in mutants of Aspergillus niger requiring lysine.

Mutants of Aspergillus niger 194A and 178 requiring lysine differ from the original prototrophic strain K10 and from each other on the course of accumulation of organic acids. In both mutants less citric acid accumulates during the first phase of cultivation but considerably more 2-oxoglutarate and 2-oxoadipate accumulate than in the original strain. Whereas in the 194A mutant this state remains unchanged also during the second phase of cultivation, in the 178 mutant oxo acids are degraded and citric acid is synthesized intensively. The accumulation of 2-oxoglutarate and 2-oxoadipate in the fermentation medium indicates that in A. niger lysine is synthesized via the homocitrate pathway.

[Experimental verification of the results of the mathematical modeling of the process of formation of alpha-amylase-nonproductive mutants of Bacillus subtilis under continous cultivation]. / Eksperimental'naia proverka rezul'tatov matematicheskogo modelirovaniia protsessa obrazovaniia na produktivnykh po al'fa-amilaze mutantov Bacillus subtilis v usloviiakh nepreryvnogo kul'tivirovaniia.

When Bacillus subtilis produces alpha-amylase in the course of continuous cultivation, it is difficult to maintain the activity at a constant level. This may be due to the formation of nonproductive mutants. Individual cells in the population have been analysed in the course of the continuous process. The composition of the population changes depending on time and the composition of the growth medium. Semisynthetic media cause selection of mutants which synthesize the enzyme at a low rate. In contrast, complex media which are more enriched in the sources of carbon and nitrogen induce accumulation of mutants with a high activity.

Variability of Aspergillus niger after treatment with N-emthyl-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.

[Amylase formation in a periodic and continuous culture of Bacillus subtilis]. / Obrazovanie amilazy v periodicheskoi i nepraryvnoi kul'ture Bacillus subtilis.

The dynamics of alpha-amylase production by two strains of Bacillus subtilis (A32 and A32.6) was studied under periodic and continuous conditions of cultivation on a chemically defined medium and on a natural medium. In the periodic culture, the highest activity of the enzyme was found during the stationary growth phase. In the conditions of chemostat, as the dilution rate from 0.05 to 0.15 hr-1, the activity of amylase remained at the same, high level for a certain lapse of time and then decreased. The rate of the decrease of alpha-amylase activity depended on the dilution rate.