Extracellular xylanase production by two thermophilic alkali-tolerant Bacillus strains in batch and continuous cultures.

Xylanase production of newly isolated thermophilic alkali-tolerant Bacillus sp. strain SP and strain BC was investigated in batch and continuous cultures. Enzyme synthesis was inducible with both strains and was observed only in xylan-containing media. Xylan from oat spelt is a better inducer than xylan from birch for strain Bacillus sp. BC while such difference was not observed for strain SP. Compared with batch cultures xylanase production of both strains increased about two times and its rate became more than four times faster in continuous cultures at a dilution rate of 0.2 h(-1).

[Biosynthesis of protein and reserve substances by yeasts growing on different substrates with limited sources of mineral nutrition]. / Biosintez belka i rezervnykh veshchestv u drozhzhei, rastushchikh na raznykh substratakh v usloviiakh limitirovaniia istochnikami mineral'nogo pitaniia.

The content of protein and reserve compounds was studied in yeast cells growing on glucose, hexadecane and ethanol in a complete medium and in media limited with a source of nitrogen, phosphorus or sulfur. It was shown that the proportion between these components characterises the direction of biosynthetic processes in the cell depending on cultivation conditions. This is strongly shifted towards protein synthesis in the period of exponential growth when constructive processes are active. When the growth is limited with the sources of mineral nutrition, the content of protein drops down abruptly while that of the reserve compounds, lipids and carbohydrates, rises. Glycogen prevails in cells grown on glucose whereas lipids are the major component of cells cultivated on hexadecane. Nitrogen, phosphorus and sulfur deficiency causes quantitative and qualitative changes in the composition of free and bound amino acids in yeast biomass. The degree of these changes depends on the nature of the growth--limiting factor.

[Conditions and dynamics of citrate, isocitrate and polyol excretion in yeast growth on glucose]. / Usloviia i dinamika ékskretsii tsitrata, izotsitrata i poliolov pri roste drozhzhei na gliukoze.

The dynamics of metabolite excretions by Candida guilliermondii, Candida zeylanoides and Torulopsis candida was studied during their batch cultivation in media with glucose excess and low concentrations of N, P or S sources; the latter were the growth limiting factors and determined the transition to phase of retardation and the stationary phase of growth. Growth limitation with the above components in the presence of a carbon source results in the following: (a) the growth becomes linear and the phase of retardation falls into two periods differing in the absolute growth rate which initially is relatively high but then decreases; (b) protein content drastically decreases while lipid content and in particular, of glycogen increases, i. e. the direction of biosynthetic processes changes; (c) intensive excretion of citrate and isocitrate begins and continues (including the stationary phase) until the carbon source is exhausted. In contrast to citrate and isocitrate, polyols are excreted throughout all growth phases (including the exponential one) and strictly periodically, i. e. these metabolites are repeatedly excreted and re-utilized. The fact that polyols are excreted during the exponential growth phase proves that their overproduction apparently is not connected with the limitation of the cultural growth.

[Metabolite excretion by yeasts of the genus Candida in media lacking sources of N, P, S, or Mg and having different carbon sources]. / Ekskretsiia metabolitov Drozhzhami roda Candida pri defitsite istochnikov N, P, S ili Mg v sredakh s razlichnymi istochnikami ugleroda.

The purpose of this work was to study the effect produced by limiting the growth of yeasts belonging to the genus Candida on the excretion of cell metabolites. Changes in the composition and quantitative ratios between substances excreted depending on the carbon source (glucose, ethanol, hexadecane) and factors limiting growth of the cultures (N, P, S or Mg sources) were examined. It has been shown that (a) limitation of the yeast growth results in the majority of cases (but not always) in the excretion of macroquantities of these or other metabolites; (b) many microorganisms differ substantially from one another in their capacity to excrete metabolites; (c) the total number of metabolites found in the medium in macroquantities in different variants of the experiment is relatively small, and all of them belong to these or other intermediates of the oxidative metabolism of the carbon source (the acids of the citric acid cycle etc.) or are involved in the process of gluconeogenesis (polyols); (d) the composition and quantitative proportions of the excreted metabolites depend on the organism, carbon source and growth limiting factor.