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Procedures for the production of endo-1,4-beta-xylanase have been developed. An active producer-Rhizopus var. microsporus BKMF-595-has been chosen, and the conditions of surface and submerged cultivation, as well as the composition of the culture medium for this strain, have been optimized to ensure maximum yield of the target enzyme. Activity of xylomicrosporin Px equaled 123 U/g, while the activity of xylomicrosporin Gx equaled 25 U/cm3. Homogeneous enzyme preparations, purified 59.44-fold and 72.6-fold, have been obtained. The dependence of endo-1,4-beta-xylanase catalytic activity on temperature and pH of the reaction medium has been studied. The enzyme has been shown to be most stable in the pH range 5.0-6.0 and to be thermostable. Amino acid composition and subunit structure of the enzyme were determined; the molecular masses of the subunits equaled 50 and 56 kDa. Carboxyl groups of glutamic and aspartic acid residues of the active center were experimentally shown to play an important role in catalysis. The potential of this enzyme for beer production has been demonstrated.

Species composition of micromycete complexes colonizing aspen, birch, and pine wood was studied. Calculation of the Sorens-Tchekanovsky similarity coefficients showed that these complexes shared a high degree of similarity. They were dominated by the representatives of the genera Penicillium, Paecilomyces, Trichoderma, and Rhizopus. Some antagonistic bacilli inhibited growth and development of wood-decay fungi in vitro and led to the formation of spheroplasts on growing hyphae. A study of possible involvement of bacillary mycolytic enzymes in the inhibition of wood-decay fungi demonstrated selectivity of their lytic effect, which was determined by the genus and species of micromycetes and did not correlate with their relative resistance to antagonists.

The capability of 26 collection micromycete strains to synthesize biotin and transform destiobiotin was investigated. Destiobiotin stimulated the biotin formation by the strains of the Aspergillus genus (except A. sclerotiorum synthesizing vitamin traces), the Fusarium genus, the Rhizopus genus (except Rh. nigricans), as well as Thighemella hyalospora and Sporotrichum sulfurescens. Among the strains tested Rhizopus delemar 1428 synthesized maximum quantities of biotin (over 300 micrograms/1). The biotin synthesis by this strain increased drastically when the fungal growth was terminated, about 90% of biotin being released into the medium. The rate of biotin synthesis and excretion grew significantly when the major portion of glucose was consumed and pH of the medium increased (to 8.0-8.2).

Biotin synthesis by the yeast Sporobolomyces pararoseus and the microscopic fungus Rhizopus delemar was studied in batch cultures at different substrate ratios in the medium. The overall (exocellular + endocellular) biotin content in the yeast was 4.5-6.0 micrograms per 1 g of biomass on different media and did not depend on the growth phase. The content of biotin in the fungus was 7.5-9.0 micrograms per 1 g of biomass and depended neither on the growth phase nor on the quantitative ratio between components of the growth medium. In contrast to the yeast, the content of exocellular biotin per 1 g of the mycelium increased with the fungal growth, and the yield of biotin was maximal (25-29 micrograms/g) at the stationary growth phase. The maximal rate of biotin synthesis by the both organisms coincided in time with their maximal growth rate.

The effect of organic and mineral nitrogen sources on the production of lipolytic enzymes and the accumulation of biomass was studied with Rhizopus microsporus UzLT-I. Addition of mineral nitrogen sources to the growth medium weakly stimulated synthesis of lipase by the fungus. The production of lipolytic enzymes was highest on media with organic nitrogen compounds, particularly yeast autolysate and fodder yeast cells (0.1: 0.25%). The lipolytic activity of the cultural broth on media with these nitrogen sources increased by 50% cf. the control.

The dynamics of growth and exolipase biosynthesis was studied in the fungus Rhizopus microsporus under laboratory and semi-industrial conditions at 28, 38 and 48 degrees C. As the temperature rises, the lag-phase as well as the exponential and stationary phases of growth are reduced while the specific growth rate increases. The accumulation of the biomass was found to correlate with the production of the enzyme which was most intensive at the end of exponential growth when the formation of spores was intensive. The greatest lipolytic activity of the cultural broth was recorded at the beginning of stationary growth of the culture. The lipolytic activity hardly changed at the stationary phase of growth and fell down abruptly when the cells died off. The temperature of 38 degrees C was optimal for the accumulation of biomass and lipase in the cultural broth. Good results were obtained at 28 degrees C, but the cultivation was prolonged by 5--7 hours. The yield of the biomass and the level of the lipolytic activity are much lower at 48 degrees C although the specific growth rate is high.

The object of this work was to study the transformation of desthiobiotin (DTB), a biotin precursor, to biotin by Rhizopus delemar which can accumulate rather large quantities of biotin in the medium. Both the growing and resting culture transform DTB at a high rate. Biotin excretion by the resting culture rises by 100% when 25 micrograms/ml of DTB are added to the medium. The content of biotin within the cells remains unchanged. L-Methionine, sodium sulfite and sodium sulfate are most effective sulfur donors for DTB transformation by the resting culture. Cystine, cysteine and elementary sulfur cannot serve as sulfur donors. The transforming activity of the mycelium is preserved for about seven days. Immobilization of the cells in agar gel and in porolon does not increase the time within which the mycelium remains in the active state.