I. S. Mysyakina

Trehalose: Chemical structure, biological functions, and practical application

Up-to-date information concerning the chemical structure and properties of trehalose, its natural occurrence and biological functions in plants, fungi, and prokaryotes, as well as its practical application, mainly in medicine and biotechnology, are reviewed. A special section deals with the role of trehalose and other protective polyols in stress processes in fungi.

Lignin: Chemical structure, biodegradation, and practical application (a review)

The review describes the natural biopolymer lignin, which is second in plant biomass abundance. It is evident now that lignin is considerably undervalued and insufficiently studied in the applied area. The review focuses on the history of the lignin discovery, methods for its extraction from plant objects, its biodegradation by fungi, the enzymes degrading lignin, and the prospects of its application in current biotechnology.

Biodiesel fuel production from lipids of filamentous fungi

The main stages in the production of biodiesel fuel from lipids of filamentous fungi belonging to the order Mucorales are described. Fungi of the family Cunninghamellaceae have been screened; the lipogenic activity of the examined strains has been assessed; and a producer generating up to 50% of lipids, represented by triacylglycerols, has been found. The substitution effect of a source of carbon and nitrogen with less expensive components (in particular, various industrial wastes) has been studied, as well as their influence on the quantity and major characteristics of the final product. An ecologically friendly method for extracting lipids from fungal mycelia, utilizing supercritical technologies, has been used. A correlation between the lipid content in the spore inoculum and the maximal lipid content in biomass has been discovered; this correlation is proposed for optimizing the biotechnology and increasing the yield of final products.

Influence of lignin and oxygen on the growth and the lipid formation of the fungus Lentinus tigrinus

During cultivation of the filamentous fungus Lentinus tigrinus on a medium containing lignin, a high oxygen content stimulated the growth of the fungus and contributed to the yield of lipids. A high content of phosphatidic acid and a reduction in the level of phosphatidylethanolamine and phosphatidylserine were first detected in the composition of phospholipids. Changes in the composition of neutral lipids, such as variation in the ratio of esterified and free sterols, have occurred; thus, the amount of sterol esters reduced simultaneously with a decrease in the content of free fatty acids. Based on the obtained results, the possible role of phosphatidic acid as a second messenger in the process of the consumption of lignin by the fungus Lentinus tigrinus is discussed.

Germination of spores of mycelial fungi in relation to exogenous dormancy

Comparative analysis of germination of asexual sporulation spores (conidia and sporangiospores) and of specific features of dormancy release was carried out for ascomycete mycelial fungi Aspergillus tamarii VKM F-64 and A. sydowii VKM F-441, as well as for zygomycete fungi Cunninghamella echinulata VKM F-663 and Umbelopsis ramanniana VKM F-582. The spores of these strains were shown to be in a state of exogenous dormancy and differed in lag phase duration and germination rate, which depended on the presence of nutrients in the medium. Only the strain C. echinulata VKM F-663 exhibited 100% spore germination, with the germination rate and lag phase duration not depending on the composition of the medium. While in A. tamarii strain VKM F-64, the total number of spores germinating on rich and poor media was also almost the same, in the absence of nutrients lag phase duration increased and the germination rate decreased. For strains U. ramanniana VKM F-582 and A. sydowii VKM F-441, the degree of spore germination in the absence of nutrients in the medium was considerably lower than on the rich medium, while the lag phase was longer. These data indicate that the spores of C. echinulata VKM F-663 are in the state of exogenous dormancy, which does not require for release any compounds except water. The spores of U. ramanniana strain VKM F-582 and of the Aspergillus strains exhibited another variant of exogenous dormancy, which required for release, apart from water, also the sources of carbon and nitrogen. Thus, the character of dormancy release may differ even within a single genus (Aspergillus).

Lipid Composition in Cell Walls and in Mycelial and Spore Cells of Mycelial Fungi

Qualitative and quantitative differences were found between the lipids of cell walls (CW), of whole mycelial cells, and of dormant cells of mucoraceous and ascomycete fungi. Thus, whole mycelial cells (WC) contained more lipids than CW. Unlike sporangiospores and conidia (exogenous dormant spores), zygotes were found to have the highest content of triacylglycerol lipids (70%). Cell walls of mucoraceous fungi contained more triacylglycerols (TAG) and less polar lipids than ascomycete lipids. While all CW and WC studied were similar in fatty acid (FA) composition, their ratio was specific for each structure: linoleic acid predominated in mycelial CW and WC, while oleic acid was predominant in the spores; this difference was especially pronounced in conidial WC. Unlike WC, in CW massive lipids may be represented not by phosphatidylethanolamine (PEA) and phosphatidylcholine (PC), but by free fatty acids (FFA), free (FSt) and etherified sterols (ESt), phosphatidic acid (PA), fatty acid methyl esters (FAME), and glycolipids (GL), which is an indication of a special functional role of CW.

Effects of conditions for obtaining sporangiospores of the inoculum on the morphology and productivity of the fungus Mucor circinelloides var. lusitanicus 12 M, a producer of γ-linolenic acid

Effects of the lipid composition of sporangiospores of the fungus Mucor circinelloides var. lusitanicus 12 M, obtained within diverse time frames using distinct nutrient media, on the morphology of the fungus in submerged cultures, the yield of the biomass, and its content of g-linolenic acid have been studied. The levels of base phospholipids and individual fractions of neutral lipids in sporangiospores correlated with the character of their germination. The spores that were characterized by a high rate of germination and gave rise to a well-developed mycelium contained more phosphatidylcholine and phosphatidylserine, but the level of diacylglycerols was low. The increase in diacylglycerols, free fatty acids, and sterols in lipids of sporangiospores of the inoculate was associated with deterioration in mycelium development, dimorphism, and a decreasing yield of the biomass of the fungus.

Synthesis of Biologically Active Lipids by the Fungus Mucor lusitanicus 306D Grown on Media with Various Composition

Growth and lipogenesis of the fungusMucor lusitanicus306D, producing γ-linoleic acid, was studied under various conditions of nitrogen and carbon nutrition. Media containing food-industry wastes, such as maize extract, molasses, and protein hydrolysate, were used. The content of γ-linoleic acid was higher when carbohydrates (glucose and molasses) were used as carbon sources and urea was used as a nitrogen source. At a high glucose concentration (100 g/l), fed batch cultivation ensured high contents of γ-linoleic acid in lipids (1 g/l). After extraction of lipids, the fungus biomass was 42% protein, containing all essential amino acids. A defatted biomass was shown to be effectively assimilated by minks.

Lipid composition of the spores of zygomycetous and ascomycetous fungi during cessation of the exogenous dormancy state

The composition of lipids and fatty acids was studied in the spores of exogenously dormant (spores 0) and germinating (spores G) spores in distilled water for sporangiospores of zygomycetous fungi Cunninghamella echinulata VKM F-663 and Umbelopsis ramanniana VKM F-582 and for conidia of ascomycetous fungi Aspergillus tamarii VKM F-64 and A. sydowii VKM F-441. Compared to spores 0, the lipids of spores G contained higher shares of unsaturated fatty acids, lower levels of massive phospholipids (phosphatidylcholine and phosphatidylethanolamine), and elevated levels of phosphatidylglycerol and phosphatidic acid. The level of cardiolipin, the main phospholipid of the mitochondrial membranes, increased when the spores of both zygomycetes exited from the dormant state. While a certain increase in the content of free and esterified sterols in the neutral lipids of the slowly germinating U. ramanniana G spores was observed, germination of sporangiospores and conidia of the studied fungi generally did not result in significant changes in the composition of the neutral lipid classes, which may be due to the fact that they are not the major reserve mobilized at the stage of exit from the dormant state.

Lipid and elemental composition as indicators of the physiological state of sporangiospores in Mucor hiemalis cultures of different ages

The number of sporangiospores used as inocula may significantly affect the development of the morphogenetic programs in mucoraceous fungi, including manifestations of dimorphism. In order to assess the physiological state of sporangiospores differing in their viability and germination patterns, lipid composition of sporangiospores from 6-, 14-, and 20-day cultures of Mucor hiemalis F-1431 was determined and the element ratios in these spores (Ca/K and P/S) were measured using X-ray microanalysis. While the lipid composition of the “old” (20 days) and “young” (6 days) spores was generally similar, older spores contained no cerebrosides, had half the level of polar lipids and γ-linolenic acid, and also contained 6 times more monoacylglycerols and 2.5 times more phosphatidic acid. The ratio of esterified to free sterols (ES/FS) characterizing the sterol storage pool was lowest in the spores from 20-day cultures. X-ray microanalysis revealed the highest P/S ratio in 6-day spores and lowest ratio in 14-day ones. Mature 14-day spores had the highest Ca/K ratio, ten times exceeding that for the 20-day spores. Higher values of P/S and Ca/K ratios in young (ripening) spores than in old 20-day spores indicate their higher metabolic activity and correlate with their higher viability and mycelial type of germination. Together with the lipid characteristics, the Ca/K and P/S ratios are the parameters which may be used to develop the criteria for assessment of the physiological state of the cells, including viable fungal sporangiospores. This complex may be also used to assess the capacity of mucoraceous fungi for dimorphism, including the species (M. hiemalis) for which this capacity has not been demonstrated previously.