The conversion of household and industrial wastes containing lignocellulose into a variety of target products (bioenergy sources, organic acids, sweeteners, etc.) involves one of the priority directions for the state environmental policy of the Russian Federation. However, the profitability of processing the substrates obtained by hydrolysis of such secondary sources of raw materials is determined by the possibility of micro-biological utilisation for not only hexoses (D-glucose, D-mannose, D-galactose), but also pentose (D-xylose, L-arabinose). The aim of this review consists in a discussion of the prospects for using microorganisms in the disposal of lignocellulose pentoses, along with problems arising in the course of the technological implementation of this process. The review provides contemporary data on the spectrum of pro- and eukaryotic microorganisms ensuring the destruction of lignocellulose and the utilisation of its structural components in natural ecosystems. A brief description of action mechanism inherited to the enzymes of ligninase, cellulose and hemicellulase complexes is presented. The main problems hindering the enzymatic hydrolysis application to multicomponent household and industrial lignocellulose wastes are identified. The factors determining the selectivity of pentosis catabolism in mycelial fungi, bacteria and yeast are examined. The spectrum of target products in bioconversion of lignocellulose pentoses, is determined with regard of their economic importance. The methods of complex microbiological utilisation of various household and agricultural wastes, as well as the possibility of involving by-products from industrial destruction of wood (acid hydrolysates and sulphite liquors) in this process, are discussed.

Изучена продукция ксилита и этанола, а также активность ключевых ферментов катаболизма D-ксилозы у мутантов дрожжей Pаchysolen tannophilus с измененным ростом на D-ксилозе, ксилите, этаноле или D-глюкозе в качестве единственного источника углерода. Угнетение активности ксилозоредуктазы с преимущественным сродством к НАДФН и ксилитдегидрогеназы до 4.40 и 4.80 мкмоль мг-1 мин-1 соответственно индуцировало накопление 0.25 г ксилита на г потребленной D-ксилозы. Наибольшая активность НАДН/НАДФН-ксилозоредуктазы и ксилитдегидрогеназы (6.00–6.80 и 6.80–8.40 мкмоль мг-1 мин-1) зафиксирована у штаммов, продуцирующих 0.24–0.26 г этанола на г D-ксилозы. Обсуждается использование мутантов Pа. tannophilus для анализа регуляции катаболизма D-ксилозы.

Production of xylitol and ethanol, as well as activities of the key enzymes of D-xylose consumption, were studied in Pachysolen tannophilus mutants with altered growth on D-xylose, xylitol, ethanol, or D-glucose as sole carbon sources. Suppressed activity of xylose reductase with preferential affinity for NADPH and of xylitol dehydrogenase to 4.40 and 4.80 μmol mg−1 min−1, respectively, resulted in accumulation of xylitol (0.25 g per 1 g D-xylose consumed). The highest levels of NADH/NADPH-xylose reductase and xylitol dehydrogenase (6.00–6.80 and 6.80–8.40 μmol mg−1 min−1, respectively) were found in the strains producing 0.24–0.26 g ethanol per 1 g D-xylose. Application of Pa. tannophilus mutants for analysis of the regulation of D-xylose catabolism in yeasts is discussed.

Изучена активность основных ферментов катаболизма D-ксилозы у мутантов ксилозоассимилирующих дрожжей Pachysolen tannophilus, селективно продуцирующих ксилит, либо этанол. Штамм, образующий ксилит, характеризовался низкими активностями ксилозоредуктазы с преимущественным сродством к НАДФН, ксилитдегидрогеназы, НАД+-зависимой малатдегидрогеназы и цитохром-с-оксидазы (4.40, 4.80, 1.87 и 0.28 мкмоль/мг мин соответственно). В клетках мутантов, продуцирующих этанол, увеличены активности НАДН/НАДФН-ксилозоредуктазы и ксилитдегидрогеназы до 6.80 и 8.60 мкмоль/мг мин, а также 1-глицерофосфатдегидрогеназы и лактатдегидрогеназы до 4.68 и 16.48 мкмоль/мг мин. Обсуждается влияние дисбаланса НАДФН/НАДН на спиртообразование и накопление ксилита.

Activity of the major enzymes of D-xylose metabolism in the mutants of xylose-utilizing yeasts Pachysolen tannophilus selectively producing xylitol or ethanol was studied. The xylitol-producing strain exhibited low activities of xylitol dehydrogenase, xylose reductase with preferential affinity to NADPH, NAD+-dependent malate dehydrogenase, and cytochrome c oxidase (4.40, 4.80, 1.87, and 0.28 μmol mg−1 min−1, respectively). The cells of the ethanol-producing mutants exhibited elevated activity of NADH/NADPH-xylose reductase, xylitol dehydrogenase, 1-glycerophosphate dehydrogenase, and lactate dehydrogenase to 6.80, 8.60, 4.68, and 16.48 μmol mg−1 min−1, respectively. Effect of the NADPH/NADH imbalance on ethanol production accumulation and xylitol accumulation is discussed.

A comprehensive experimental investigation of the effect of the Reynolds number on the degeneration law for turbulence generated by biplanar and wicker grids is carried out over a wide range of the grid geometry parameters and the flow velocity. It is established that an increase in the flow velocity leads to an increase in the turbulence intensity at a given distance from the biplanar grid and a decrease in the turbulence decay rate downstream of the grid. An empirical relation between the turbulence intensity behind the grid, on the one hand, and the relative distance x/M from the grid and the Reynolds number based on the grid rod diameter and the flow velocity at the grid mesh center, on the other hand, is proposed. For the same relative distance x/M from the grid the intensity of wicker-grid turbulence is higher than in the case of the flow past a biplanar grid.

Conditions favoring differentiation and stabilization of the life cycle of the yeast Pachysolen tannophilus have been studied. When concentrations of the carbon source in the medium were lower than 100 g/l, it was found to be favorable to the mating of vegetative cells, both haploid and diploid. The addition of nitrogen and sulfur sources to the medium influenced the life phases of haploid cells and partially stabilized the vegetative growth of diploid cells. Enrichment of the nutrient medium with potassium, vitamins, and microelements was shown to be necessary for the formation and maturation of conjugated ascospores. Microelements, vitamins. and phosphorus in excessive amounts activated conjugation but did not provide for the distinct phases of formation of unconjugated asci and spores in the diploid cells. Possible reasons for the unstable diplophase in the yeast P tannophilus have been discussed.

The activities of xylitol dehydrogenase and xylose reductase in the yeasts Candida shehatae, C. didensiae, C. intermediae, C. tropicalis, Kluyveromyces marxianus, Pichia stipitis, P. guillermondii, Pachysolen tannophilus , and Torulopsis molishiama were studied at different oxygen transfer rates (OTRs) to the fermentation medium (0, 5, and 140 mmol O 2 /(l h)). The activities of these enzymes were maximum in the yeasts P. stipitis and C. shehatae. The xylitol dehydrogenase of all the yeasts was NAD + -dependent, irrespective of the intensity of aeration. The xylose reductase of the yeasts C. didensiae, C. intermediae, C. tropicalis, Kl. marxianus, P. guillermondii , and T. molishiama was NADPH-dependent, whereas the xylose reductase of P. stipitis, C. shehatae , and Pa. tannophilus was specific for both NADPH and NADH. The effect of OTR on the activities of the different forms of xylitol dehydrogenase and xylose reductase in xylose-assimilating yeasts is discussed.

The ability to assimilate D-glucose and D-xylose was studied in 21 yeast species of the following genera: Candida, Kluyveromyces, Pachysolen, Pichia, and Torulopsis. All the cultures fermented D-glucose with the formation of ethanol. During the assimilation of D-xylose, ethanol was produced by P. stipitis and C. shehatae, whereas xylitol was produced by C. didensiae, C. intermediae, C. parapsilosis, C. silvanorum, C. tropicalis, K. fragilis, K. marxianus, P. guillermondii, and T. molishiama. The yeast P. tannophilus produced comparable amounts of both alcohols. The possible use of xylose-assimilating yeasts for the production of xy-litol and ethanol is discussed.

The activity and the cofactor specificity of xylose reductase and xylitol dehydrogenase were studied in extracts of yeasts from the genera Candida, Kluyveromyces, Pachysolen, Pichia, and Torulopsis grown under microaerobic conditions. It was found that xylitol dehydrogenase in all of the yeast species studied is specific for NAD + ; xylose reductase in the xylitol-producing species C. didensiae, C. intermediae, C. parapsilosis, C. silvanorum, C. tropicalis, Kl. fragilis, Kl. marxianus, P. guillermondii , and T. molishiama is specific for NADPH; and xylose reductase in the ethanol-producing species P. stipitis, C. shehatae , and Pa. tannophilus is specific for both NADPH and NADH.

The results of an experimental investigation of the effect of the streamwise pressure gradient in a turbulent boundary layer on the permissible height of the surface roughness of bodies in an incompressible fluid flow are presented. The permissible roughness Reynolds number for which the characteristics of the turbulent boundary layer remain the same as in the case of flow past a smooth surface is determined.

The results of a systematic experimental study of the integral scale of turbulence generated by manipulators, such as grids and honeycombs, are presented. On the basis of the statistical processing of a large body of the experimental data (for 29 grids and 19 honeycombs) the dependence of the turbulence scale behind a manipulator on the relative downstream distance and the Reynolds number is established. A technique for reducing honeycomb flow conditions to those of flow past an equivalent grid has been developed. This makes it possible to present the experimental data for grids and honeycombs in the same functional form.

The results of a systematic experimental study of the flow turbulence level effect on the heat transfer and Reynolds analogy coefficients over a wide range of the relevant parameters (the turbulence intensity and scale and the Reynolds number) are presented. The notion of the equivalent flow turbulence, which unifies the above-mentioned parameters, is introduced. It is established that the skin friction and heat transfer coefficients increase with the equivalent turbulence, while the Reynolds analogy coefficient remains unchanged.

The characteristics of honeycombs of different shapes and sizes used for reducing free-stream turbulence in wind tunnels have been experimentally investigated. The optimum geometric dimensions of the honeycomb and its optimum location in the wind tunnel necessary to ensure a minimum level of turbulence in the working section have been determined.

The data on preparation and application of microbial sterols are reviewed. The ways of optimization of ergosterol production are discussed. The microbiological techniques for obtaining other sterols are proposed based on using specific inhibitors and mutants. The data concerning chemical and biological transformation of yeast sterols to androstane hormones and D vitamins are presented.