Journal of Fermentation and Bioengineering最新文献

Modulation of the enantioselectivity of two lipases exhibiting different specificities in the esterification of 2-octanol with lauric acid was investigated by utilizing surfactant-coating and molecular imprinting techniques. The enantioselectivity of the surfactant-coated lipase from Pseudomonas cepacia (PS) was enhanced in the presence of (R)-2-octanol as a print molecule, whereas the enantioselectivity of the lipase from Candida cylindracea (AY) was hardly changed by the imprinting technique. In the case of lipase AY, however, the selectivity of the native enzyme toward the (R)-isomer was changed to a preference for the (S)-isomer as a result of being coating with surfactant molecules. The molecular imprinting effect was prominent in the case of lipase PS, its enantioselectivity in the formation of 2-octanoate in isooctane being enhanced around two-fold compared with that of the native enzyme.

This paper studies the temperature effect on the specific growth rate of the microorganisms (μ_c) as particular aspect of the mathematical relationships between μ_c of Thiobacillus ferrooxidans and the concentrations of substrate (ferrous iron) and product (ferric iron). Until now, there have been few studies of this relationship; also, there has been little work studying the influence of temperature on growth kinetics of this bacteria. In this paper, an extensive experimental phase has been developed, with the aim of determining with precision the influence of temperature on the maximum specific growth rate (μ_max). The influence on the growth rate of T. ferrooxidans exerted by the initial pH of the medium and by agitation rate has also been studied.

Oleyl alcohol and oleic acid were esterified using lipase-surfactant complex (LSC) in a solvent-free reaction system. LSC showed a higher reaction rate than the crude enzyme in the reaction system. Optimum LSC activity was obtained at 180 mg/g-solution water addition. A preliminary study of the membrane reactor system using a microfiltration membrane and a solvent-free reaction was performed, and the feasibility of the reactor system was confirmed.

Strawberry (Fragaria ananassa cv. Shikinari) cell suspension cultures carried out in shake flasks for 18 d were closely examined for cell growth, anthocyanin synthesis and the development of pigmented cells in relation to the uptake of carbohydrate, extracellular PO₄, NO₃, NH₄, and calcium. Cell viability, extracellular anthocyanin content, pH and electrical conductivity of the broth were also monitored. The specific growth rate of strawberry cells at exponential phase was 0.27 and 0.28 d⁻¹ based on fresh and dry weight, respectively. Anthocyanin synthesis was observed to increase continuously to a maximum value of 0.86 mg/g fresh cell weight (FCW) at day 6, and was partially growth-associated. Anthocyanin synthesis was linearly related to the increase in pigmented cell ratio, which increased with time and reached a maximum value of ca. 70% at day 6 due to reduction in cell viability and depletion of substrate. Total carbohydrate uptake was closely associated with increase in cell growth, and glucose was utilized in preference to fructose. Nitrate and ammonia were consumed until 9 d of culture, but phosphate was completely absorbed within 4 d. Calcium was assimilated throughout the growth cycle. After 9 d, cell lysis was observed which resulted in the leakage of intracellular substances and a concomitant pH rise. Anthocyanin was never detected in the broth although the broth became darkly pigmented during the lysis period. This suggests that anthocyanin was synthesized only by viable pigmented cells, and degraded rapidly upon cell death and lysis. Based on the results of kinetic analysis, a model was developed by incorporating governing equations for the ratio of pigmented cells into a Bailey and Nicholson's model. This was verified by comparison with the experimental data. The results suggest that the model satisfactorily describes the strawberry cell culture process, and may thus be used for process optimization.

Riboflavin-requiring mutants were isolated from Corynebacterium ammoniagenes. One of the mutants, RK122, accumulated 6,7-dimethyl-8-ribityllumazine (DMRL), a direct precursor of riboflavin, in the culture medium. Chromosomal DNA fragments that complement the riboflavin requirement of RK122 were cloned and sequenced. Sequence analysis revealed that the structure of the riboflavin biosynthetic genes of C. ammoniagenes showed significant similarity to those of Bacillus subtilis.

Biosynthetically blocked mutants isolated from the β-rhodomycin-producing Streptomyces violaceus A262 strain SC-7 and daunomycin-producing Streptomyces sp. D788 strain G1-1 were found to accumulate maggiemycin in their culture broths. Bioconversion tests using mutants that did not produce these antibiotics also proved that maggiemycin is a common precursor in the biosynthesis of β-rhodomycin and daunomycin.

The addition of 5.6 mM crotonic acid to Streptomyces hygroscopicus var. ascomyceticus fermentations producing immunomycin reduced the level (as a percentage of immunomycin) of the major analog impurity L-683,795 from 6.7% for the control to 2.5%. Crotonic acid supplementation did not increase the titer of immunomycin and appeared to suppress production at higher concentrations. The addition of butyrate or valine, which can be catabolized to butyrate, at the concentrations used for crotonic acid were not as effective in reducing the percentage of L-683,795. Importantly, 5.6 mM crotonic acid supplementation reduced the L-683,795 level from 7.0% to 4.5% at the 23-l fermentor scale indicating that the effect of crotonic acid supplementation is scaleable to at least the laboratory bioreactor scale. Moreover, crotonyl-coenzyme A reductase (crotonyl-CoA reductase) activity could be detected in cell extracts. This work suggests that crotonic acid can be converted to butyrate through the activity of crotonyl-CoA reductase and can serve as a source of exogenously added C-4 precursor for macrolide biosynthesis.

Alkaline pulping liquors are problematic for anaerobic treatment due to their toxicity to methanogens and their relatively large fraction of inert lignin. In previous research, toxicity due to wood extractives was shown to be highly eliminated during aerobic wastewater treatment, but not during anaerobic treatment. These observations have led to the proposal of a detoxification strategy denominated upfront dilution, based on the sequenced anaerobic-aerobic treatment of the pulping liquor, recirculating the aerobic effluent to dilute the incoming influent to sub-toxic concentrations. In this study, the treatment of highly toxic hemp stem wood black liquor (HSWBL) in lab-scale UASB reactors with upfront dilution was compared with direct anaerobic treatment and with direct aerobic treatment. Direct anaerobic treatment of 12 g COD/l HSWBL led to almost complete inhibition of the methanogenic activity within 14 d. However, recirculation of 75% of the aerobic post-treatment effluent for upfront dilution of the toxic HSWBL, enabled anaerobic treatment at loading rates up to 21.5 g COD/l_UASB·d without significant inhibition of the methanogenic activity. Extensive detoxification was confirmed during anaerobic-aerobic treatment of 20 g COD/l HSWBL recirculating 86% of the aerobic effluent. COD and BOD removal was 72% and 97%, respectively, after anaerobic-aerobic treatment at an overall loading rate of 3.6 g COD/l·d, while 30–35% of the incoming COD was recovered as methane. Batch-assays demonstrated significant detoxification after anaerobic-aerobic treatment of HSWBL. Treatment efficiencies and detoxification during anaerobic-aerobic and aerobic treatment were similar. However, the anaerobic-aerobic treatment system provided 50% lower surplus sludge production, production of 0.16 m³ methane/kg COD_removed as an energy source, less nutrient dosage and substantial reductions in aeration costs. During anaerobic-aerobic treatment as well as aerobic treatment significant lignin removal was obtained, ranging from 28–58%. Lignin removal could be attributed to biodegradation of low molecular weight lignin (MW < 2.2 kD). The lignin which survived biological treatment was extensively polymerized to MW of > 34 kD.