The literature review is devoted to the analysis of factors regulating the utilization of D-xylose and L-arabinose, structural components of various plant biomass wastes, by soil microscopic fungi. The data on transport, initial stages of catabolism of these pentoses in the context of microorganism adaptation to starvation conditions, osmotic and oxidative stresses are systematized. The possibilities of using soil microscopic fungi for complex utilization of plant wastes associated with the production of renewable energy sources, sugar substitutes, and organic acids are discussed.

To ensure development sustainability, the linear economic approach is being transformed into a cyclical model. For the pulp and paper industry (PPI), which occupies a significant place in the Russian economy, the shift of circular principles to the field of bioeconomics is becoming more important. This requires the development of basic biotechnological approaches implemented in closed cycles (biorefining). The aim of this study was to develop the biotechnological foundations of the circular economic system of the pulp and paper industry. To achieve the goal, the factors for the implementation of the circular mechanism in the pulp and paper industry were established. The composition of pulp and paper waste was systematized, taking into account the places of their occurrence; the directions and forms of the biorefining of pulp and paper secondary renewable resources were determined; and the principal possibility of obtaining bioethanol, based on the whole complex of sugars from cellulose production wastes, is shown. A wide range of general scientific methods was involved (analysis, synthesis, classification, modeling, etc.). Statistical methods were used to process experimental results in the field of pulp and paper waste bioconversion. The biotechnologies involved included methods of destruction, detoxification, and conversion of useful resources into secondary raw materials and final products. From the standpoint of the environmental approach, there are serious efficiency imbalances in the pulp and paper industry, which justify the implementation of circular mechanisms for organizing economic systems. The overall efficiency is ensured by the use of renewable resources and obtaining environmental effects. Algorithms and parameters of green biotechnological regulations for pulp and paper industry waste recycling provide the possibility of microbiological production of a complex of products: biocomposites, bioplastics, medical products, fertilizers, feed additives, vitamin supplements, and bioenergy resources. A strategy for the efficient biochemical processing of pulp and paper waste into green ethanol was determined. The possibility of increasing the efficiency of alcoholic fermentation using various biocatalysts was experimentally confirmed. The technological features of this method, associated with the need for microaerobic fermentation modes, were determined.

The prospects for obtaining bioethanol based on secondary bioresources of the pulp and paper industry are discussed in order to close economic cycles. The transformation of sugars of acidic hydrolyzate of deciduous wood into bioethanol by batch culture of a selected strain of the yeast Saccharomyces cerevisiae with a combination of various xylose-assimilating yeasts was studied. The ethanol yield from hexose`s part was 46% from fermented sugars, its concentration reached to 9,0±0,6 g l-1. The use of pentose sugars under microaerobic conditions (concentration of dissolved oxygen 0.5-3.0%) gave the efficiency of ethanol production up to 26.7 - 35.5% from fermented sugars. The ethanol concentration in terms of the pentose`s fraction was 3.9-4.5 g l-1 (the yeast Pachysolen tannophilus); 5.2 g l-1 (the yeast Candida tropicalis); 5.6 g l-1 (the yeast Candida shehatae). The total amount of ethanol obtained from both hexose and pentose parts after distillation was 4.2-4.6 g (5.2-5.7 ml) with alcohol by volume 96%.

The paper considers theoretical data on the mechanisms of the formation of reactive oxygen species (ROS) and the transduction of stress signals in plant cells. The negative effects of ROS with excessive generation are described. A method of protoplast isolation and a fluorescent microscopy were selected for the experiments. Also, in this work, a comparative analysis of the production of ROS during hypoxia and reaeration for agricultural plants that are differently resistant to the described stress is carried out. Based on the results of the experimental part of the work, conclusions were drawn and the practical application of this study was described.

The key catabolic enzymes of D-xylose, an important structural component of different agricultural wastes, were studied in cells of mutant strains of the xylose-assimilating yeast Pachysolen tannophilus. The evaluation of catalytic activity and cofactor specificity of xylose reductase (ЕС 1.1.1.307) and xylitol dehydrogenase (ЕС 1.1.1.9) confirmed the dependence of intracellular catabolic pathway for D-xy lose on the NAD×H/NADP×H ratio, formed under microaerobic conditions. The study of total activity of some NAD/NAP×H-dependent dehydrogenases revealed the metabolic characteristics of the yeast cells, which could ensure selective ethanol or xylitol production. Thus, the efficient involvement of D-xylose into the Embden–Meyerhof–Parnas pathway provided not only the high activities of xylose reductase and xylitol dehydrogenase, but also of 1-glycerophosphate dehydrogenase (EC 1.1.1.8) and lactate dehydrogenase (ЕС 1.1.1.27), respectively. The inhibition of activity of these enzymes led to selective production of xylitol from D-xylose. On the base of the experimental results, the principles of metabolic engineering of xylose-assimilating yeasts were formulated. The possibility of bioethanol and xylitol production from different agricultural wastes using xyloseassimilating yeasts are discussed.

In this paper, we consider the process of producing biogas with a high methane content when used as a co-substrate for fermentation of plant residues of microalgae. Microalgae Chlorella sorokiniana are a valuable source for obtaining valuable components such as lipids, pigments, proteins, chlorophyll and others. After the extraction of valuable components, residual biomass is formed, which requires further disposal. In this experiment, the digestion process is carried out using an inoculant — lyophilically dried activated sludge from sewage treatment plants in Hamburg in the amount of 450 ml and residual biomass of the microalga Chlorella sorokiniana in the amount of 2.1 g. The studies were carried out in the Anaerobes Test system AMPT-II system. Fermentation produces 205 ml of methane gas.

The xylose-assimilating capacity of yeast Pachysolen tannophilus to utilize sugars in spent sulphite liquor samples (pulp mill waste) with a different concentration of hexoses and pentoses was studied. The consumption of hexoses (D-glucose, D-mannose, D-galactose) and pentose (D-xylose) in such substrates reached 90.0-97.5% and 49.12-67.45%, respectively. The ethanol production from sugars in spent sulphite liquor by different strains of the yeast P. tannophilus was demonstrated. The maximum specific rate and ethanol yield reached 9.32-11.45 g l-1 and 0.28-0.37 g g sugars-1, respectively. Thus, the principle possibility of using xylose-assimilating P. tannophilus yeast to obtain bioethanol from sulfite liquor with a different ratio of hexoses and pentoses was proved. According to theoretical calculations, this method will provide up to 42.6 liters of ethanol from 100 kg of sulfite liquor containing 55.6% D-xylose, 24.7% D-glucose, 8.7% D-mannose, 7.6% D-galactose, 3.7% L-arabinose. A future-oriented perspective on bioethanol production from pulp and paper industry wastes by the yeast P. tannophilus is considered.

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.

This work presents economical and ecological advances of microbiological utilization of inedible sources of plant biomass, procedure which is associated with bioethanol obtaining. We study influence of forced aeration and initial concentration of biomass of xylose-assimilating yeast P. tannophilus Y-1532/B2 on ethanol output from various xylose-containing substrates during periodical fermentation. The highest ethanol output is observed for OTR values equal to 5.0-8.0 mMole/l×h and yeast seeding density equal to 0.25 g a.d.s./g of substrate sugars. We show the possibility for intensification of ethanol obtaining technology from xylose-containing substrates. This was made using traditional biotechnological approaches of fermentation productions by optimization parameters of forced aeration of the fermentation medium and density of P. tannophilus biomass seeding. The obtained results might be used as initial parameters for calculation of laboratory regulations of complex microbiological utilization of secondary inedible sources of plant biomass of various origin and content. Industrial implementation of this technology will allow one to increase the economical coefficient of ethanol production from secondary inedible sources of plant biomass for 59.7-96.8% due to fermentation of D-xylose.

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.

The copulation activity and hybrid formation efficiency have been studied in the xylose-assimilating yeast Pachysolen tannophilus. It was shown that the presence of 2% D-glucose, 0.5% yeast extract, and 2% agarose in the growth medium provided for the highest frequencies of hybrid formation. Atypical hybrid cultures similar in morphophysiological characteristics to native haploid strains of P. tannophilus were revealed in the course of hybridization. The genesis mechanism of such culture and the reasons for the restricted applicability of hybridological analysis to genetic studies of P. tannophilus are discussed.

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.