Journal of Fermentation Technology最新文献

γ-Glutamylglycylglycine (γ-GluGlyGly) was formed through the γ-glutamyltranspeptidase (GGT) reaction catalyzed by glutaminase in a water extract of wheat bran koji obtained with Aspergillus oryzae MA-27-IM. The yield of γ-GluGlyGly was about 18% from l-glutamine in a reaction mixture containing 50 mM l-glutamine, 50 mM glycylglycine, and the extract (0.1 unit ml as GGT activity) in a 100 mM Tris-HCl buffer solution (pH 7.2), which was incubated for 7 h at 30°C. The γ-GluGlyGly formed was purified by ion exchange chromatographies, and the identified by chemical and enzymatic methods as well as by infrared and PMR spectroscopic analyses.

Temperature-sensitive mutants (TS-1 and TS-7) of a thermotolerant yeast, Hansemula polymorpha CK-1, were isolated. The mutants were unable to grow at 50°C, the maximum growth temperature of the wild type. Mutants TS-1 and TS-7 grown at 20°C showed 33 and 50% viabilities after 6 h of incubation of 50°C, respectively. Mutant TS-1 showed little variation of the degree of fatty acid unsaturation (1.26–1.28/mol) and mutant TS-7 had an almost constant sterol/phospholipid molar ratio (0.31–0.34) at 20, 30 and 40°C, although the wild type had a decrease of the degree of fatty acid unsaturation from 1.56 at 20°C to 1.30 at 40°C and an increase of the sterol/phospholipid molar ratio from 0.26 at 20°C to 0.54 at 40°C.

The chemical structures of cell wall mannans and β-glucans from two Saccharomyces cerevisiae mutants, N3 and N3-8, which have morphological alterations and fragile cell walls, were compared with a wild type strain. Acetolysis and methylation analysis of mutant mannans indicated that both N3 and N3-8 mutant mannans lacked α-1,2-mannosyl side chains which are normally present. Structures of alkali-soluble β-glucans from N3 and N3-8 mutant cells were also different from that of wild type cells in the ratio of 1,6-linkages to 1,3-linkages. The mutant glucans have much higher ratios of β-1,6-linkages (2 times for N3 mutant, 4 times for N3-8 mutant) than wild type glucan.

The fungus Fusarium oxysporum was cultivated on glucose and lactose medium in a 2 l bioreactor to evaluate its carbon conversion efficiency. The initial optimization of culture conditions indicated NH₄NO₃ or NH₄Cl as the best N source at a C/N ratio between 1:4.5 to 1:11.5 at 1% glucose concentration. The pattern of allocation of the substrate carbon and energy into the production of biomass, carbon dioxide, and heat during growth was identified by applying mass and energy balance equations. It is indicated that glucose-containing substrates are better for SCP production from the organism than substrates with lactose.

The effect of glucose feeding on bacitracin production was investigated by fed-batch culture of Bacillus licheniformis. In batch culture, bacitracin secretion was induced after the glucose initially contained in the medium was completely consumed. The concentration of bacitracin, however, increased to no more than 340 units·ml⁻¹ in the batch cultivations. Therefore, additional glucose was supplied after exhaustion of the initial glucose. The effect of glucose feeding on bacitracin biosynthesss was investigated in two ways, the pH-stat modal feeding method and the CO₂-dependent feeding method. A kinetic study of bacitracin production found that some glucose was necessary, even during the bacitracin production phase. Excessive feeding of glucose, however, caused a reduction in bacitracin biosynthetic activity. When 50 g·l⁻¹ of defatted soy bean meal (SBM) was used, the bacitracin concentration reached 670 units·ml⁻¹ with the pH-stat modal feeding method and 610 units·ml⁻¹ with the CO₂-dependent feeding method, respectively. The yield of bacitracin from consumed glucose was better for the pH-stat method. Using this control strategy, the highest concentration of bacitracin (940 units·ml⁻¹) was obtained with 150 g·l⁻¹ of SBM.

Denitrifying growth characteristics of Rhodobacter shaeroides S were examined in batch and continuous cultures under anaerobic-dark and -light conditions. Growth yield based on the electron equivalent, Y_eq., in anaerobic-dark conditions was 2–3 times lower than that in aerobic-dark conditions (aerobic-heterotropic growth). Under anaerobic-light conditions, denitrifying growth was observed with photosynthetic growth, but decreased with the increase of light intensity. The value of Y_eq. in anaerobic-light conditions increased with the increase of light intensity. This phenomenon could be explained as the change of the fraction of cell mass grown by denitrification and photosynthesis in the total cell mass from the energetic analysis.

The effects of seeding on the thermophilic composting of household organic waste were examined by measuring the changes in CO₂ evolution rate, temperature, conversion of volatile matter, pH, and microbial succession in the composting reaction. The courses of the above values differed substantially between the seeded and nonseeded experiments. The rises in temperature and pH, as well as the appearance of large peaks in the rate of CO₂ evolution occurred at earlier times in the seeded composting than in the nonseeded one. Furthermore, the final conversion of volatile matter was greater in the seeded composting than in the nonseeded one. The analysis of microbial succession indicated that the seeded composting was accelerated both in mesophilic and thermophilic stages.

For the simultaneous saccharification and alcohol fermentation (SSF) of corn, cassava and naked barley requiring no heat treatment, the use of freely syuspended glucoamylase-cell, cell immobilized and glucoamylase-cell coimmobilized systems in Ca-alginate was investigated.

In these systems, 0.2% glucoamylase was used for both the free glucoamylase-cell and cell immobilized systems, whereas 1.0% of the enzyme was used for the glucoamylase cell coimmobilized system.

The SSF of corn, cassava and naked barley was successfully carried out as follows; group A with heat treatment and group B without heat treatment using the glucoamylase-cell suspende system. The conversion yield (Y_p/s0) in the cell immobilized system was increased by the heat treatment of corn and cassava but not of naked barley. The conversion yield was remarkably increased using the coimmobilized system corn and cassava, whereas naked barley gave the same yield as in the free glucoamylase-cell suspended system.

Three thermophilic Clostridium strains were isolated from soil as cellulose-fermenting bacteria wich produced ethanol, lactic acid, and acetic acid from cellulose at 60°C. To increase ethanol productivity, strains no. 187 was mutated with N-methyl-N′-nitro-N-nitrosguanidine. The resultant mutant, no 187-102-27, was superior to the original strain in ethanol production, and produced less lactic and acetic acid. The activities of some enzymes involved in the biosynthesis of the lactic and acetic acid of mutant no. 187-102-27 were lower than those of the original strain. These results are highly consistent with the acid production of the mutant strain being low.

Aspergillus niger LCF no. 9 from a laboratory collection synthesized proteolytic enzymes active at semi-alkaline pH in high yield (90 PU casein/ml extract in 24 h). As these enzymes are inducible, the strain was grown on various protein-containing substrates, namely defatted soy, rapeseed, and sunflower cake, and ground lupin seeds. Soy cake proved best. Optimal fermentation conditions were defined and the process was extended to pilot scale. Since the proteases are highly unstable in the fermenting medium, rapid means of identifying the production optimum and of stopping breakdown of the enzymes were required: Detection of hydrolysis of benzoyl arginine paranitroanilide and injection of nitrogen provided a solution.