Monascus kaoliang CBS 302.78 immobilized in polyurethane foam using iso-propanol as co-substrate: Optimized immobilization conditions of a fungus as biocatalyst for the reduction of ketones

A Brief Introduction to the Polyurethanes According to the Principles of Green Chemistry

Polyurethanes are most often called “green” when they contain natural, renewable additives in their network or chemical structure, such as mono- and polysaccharides, oils (mainly vegetable oils), polyphenols (e.g., lignins, tannins), or various compounds derived from agro-waste white biotechnology (Principle 7). This usually results in these polyurethanes obtained from less hazardous substrates (Principle 4). Appropriate modification of polyurethanes makes them susceptible to degradation, and the use of appropriate processes allows for their recycling (Principle 10). However, this fulfilment of other principles also predisposes them to be green. As in the production of other polymer materials, the synthesis of polyurethanes is carried out with the use of catalysts (such as biocatalysts) (Principle 9) with full control of the course of the reaction (Principle 11), which allows maximization of the atomic economy (Principle 2) and an increase in energy efficiency (Principle 6) while minimizing the risk of production waste (Principle 1). Moreover, traditional substrates in the synthesis of polyurethanes can be replaced with less toxic ones (e.g., in non-isocyanate polyurethanes), which, at the same time, leads to a non-toxic product (Principle 3, Principle 5). In general, there is no need for blocking compounds to provide intermediates in the synthesis of polyurethanes (Principle 8). Reasonable storage of substrates, their transport, and the synthesis of polyurethanes guarantee the safety and the prevention of uncontrolled reactions (Principle 12). This publication is a summary of the achievements of scientists and technologists who are constantly working to create ideal polyurethanes that do not pollute the environment, and their synthesis and use are consistent with the principles of sustainable economy.

Enhanced whole-cell biotransformation of 3-chloropropiophenone into 1-phenyl-1-propanone by hydrogel entrapped Chlorella emersonii (211.8b)

OBJECTIVES

This study focuses on dehalogenation of halogenated organic substrate (3-Chloropropiophenone) using both free and hydrogel entrapped microalgae Chlorella emersonii (211.8b) as biocatalyst. We aimed at successful immobilization of C. emersonii (211.8b) cells and to assess their biotransformation efficiency.

RESULTS

Aquasorb (entrapping material in this study) was found to be highly biocompatible with the cellular growth and viability of C. emersonii. A promising number of entrapped cells was achieved in terms of colony-forming units (CFUs = 2.1 × 10⁴) per hydrogel bead with a comparable growth pattern to that of free cells. It was determined that there is no activity of hydrogenase that could transform 1-phenyl-2-propenone into 1-phenyl-1-propanone because after 12 h the ratio between two products (0.36 ± 0.02) remained constant throughout. Furthermore, it was found that the entrapped cells have higher biotransformation of 3-chloropropiophenone to 1-phenyl-1-propanone as compared to free cells at every interval of time. 1-phenyl-2-propenone was excluded from the whole-cell biotransformation as it was also found in the control group (due to spontaneous generation).

CONCLUSION

Hence, enhanced synthesis of 1-phenyl-1-propanone by entrapped Chlorella (211.8b) can be ascribed to either an enzymatic activity (dehalogenase) or thanks to the antioxidants from 211-8b, especially when they are in immobilized form. The aquasorb based immobilization of microalgae is highly recommended as an effective tool for exploiting microalgal potentials of biocatalysis specifically when free cells activities are seized due to stress.

Highly enantioselective synthesis of (R)-1,3-butanediol via deracemization of the corresponding racemate by a whole-cell stereoinverting cascade system

Background

Deracemization, the transformation of the racemate into a single stereoisomeric product in 100% theoretical yield, is an appealing but challenging option for the asymmetric synthesis of optically pure chiral compounds as important pharmaceutical intermediates. To enhance the synthesis of (R)-1,3-butanediol from the corresponding low-cost racemate with minimal substrate waste, we designed a stereoinverting cascade deracemization route and constructed the cascade reaction for the total conversion of racemic 1,3-butanediol into its (R)-enantiomer. This cascade reaction consisted of the absolutely enantioselective oxidation of (S)-1,3-butanediol by Candida parapsilosis QC-76 and the subsequent asymmetric reduction of the intermediate 4-hydroxy-2-butanone to (R)-1,3-butanediol by Pichia kudriavzevii QC-1.

Results

The key reaction conditions including choice of cosubstrate, pH, temperature, and rotation speed were optimized systematically and determined as follows: adding acetone as the cosubstrate at pH 8.0, a temperature of 30 °C, and rotation speed of 250 rpm for the first oxidation process; in the next reduction process, the optimal conditions were: adding glucose as the cosubstrate at pH 8.0, a temperature of 35 °C, and rotation speed of 200 rpm. By investigating the feasibility of the step-by-step method with one-pot experiment as a natural extension for performing the oxidation–reduction cascade, the step-by-step approach exhibited high efficiency for this cascade process from racemate to (R)-1,3-butanediol. Under optimal conditions, 20 g/L of the racemate transformed into 16.67 g/L of (R)-1,3-butanediol with 99.5% enantiomeric excess by the oxidation–reduction cascade system in a 200-mL bioreactor.

Conclusions

The step-by-step cascade reaction efficiently produced (R)-1,3-butanediol from the racemate by biosynthesis and shows promising application prospects.

Combination of multi-enzyme expression fine-tuning and co-substrates addition improves phenyllactic acid production with an Escherichia coli whole-cell biocatalyst

The aim of this study was to develop an environmentally safe and efficient method for phenyllactic acid (PLA) production using whole-cell cascade catalysis with l-amino acid deaminase (l-AAD), lactate dehydrogenase (LDH), and formate dehydrogenase (FDH). The PPA titer was low due to relatively low expression of LDH, intermediate accumulation, and lack of cofactors. To address this issue, ribosome binding site regulation, gene duplication, and induction optimization were performed to increased the PLA titer to 43.8 g/L. Then co-substrates (glucose, yeast extract, and glycerol) were used to increase NADH concentration and cell stability, resulting that the PLA titer was increased to 54.0 g/L, which is the highest reported production by biocatalyst. Finally, glucose was replaced with wheat straw hydrolysate as co-substrate to decrease the cost. Notably, the strategies reported herein may be generally applicable to other whole-cell cascade biocatalysts.

Progress in biocatalysis with immobilized viable whole cells: systems development, reaction engineering and applications

Viable microbial cells are important biocatalysts in the production of fine chemicals and biofuels, in environmental applications and also in emerging applications such as biosensors or medicine. Their increasing significance is driven mainly by the intensive development of high performance recombinant strains supplying multienzyme cascade reaction pathways, and by advances in preservation of the native state and stability of whole-cell biocatalysts throughout their application. In many cases, the stability and performance of whole-cell biocatalysts can be highly improved by controlled immobilization techniques. This review summarizes the current progress in the development of immobilized whole-cell biocatalysts, the immobilization methods as well as in the bioreaction engineering aspects and economical aspects of their biocatalytic applications.

Non-Conventional Yeasts Whole Cells as Efficient Biocatalysts for the Production of Flavors and Fragrances

The rising consumer requests for natural flavors and fragrances have generated great interest in the aroma industry to seek new methods to obtain fragrance and flavor compounds naturally. An alternative and attractive route for these compounds is based on bio-transformations. In this review, the application of biocatalysis by Non Conventional Yeasts (NCYs) whole cells for the production of flavor and fragrances is illustrated by a discussion of the production of different class of compounds, namely Aldehydes, Ketones and related compounds, Alcohols, Lactones, Terpenes and Terpenoids, Alkenes, and Phenols.

Biocatalytic anti-Prelog reduction of prochiral ketones with whole cells of Acetobacter pasteurianus GIM1.158

Background

Enantiomerically pure alcohols are important building blocks for production of chiral pharmaceuticals, flavors, agrochemicals and functional materials and appropriate whole-cell biocatalysts offer a highly enantioselective, minimally polluting route to these valuable compounds. At present, most of these biocatalysts follow Prelog’s rule, and thus the (S)-alcohols are usually obtained when the smaller substituent of the ketone has the lower CIP priority. Only a few anti-Prelog (R)-specific whole cell biocatalysts have been reported. In this paper, the biocatalytic anti-Prelog reduction of 2-octanone to (R)-2-octanol was successfully conducted with high enantioselectivity using whole cells of Acetobacter pasteurianus GIM1.158.

Results

Compared with other microorganisms investigated, Acetobacter pasteurianus GIM1.158 was shown to be more effective for the reduction reaction, affording much higher yield, product enantiomeric excess (e.e.) and initial reaction rate. The optimal temperature, buffer pH, co-substrate and its concentration, substrate concentration, cell concentration and shaking rate were 35°C, 5.0, 500 mmol/L isopropanol, 40 mmol/L, 25 mg/mL and 120 r/min, respectively. Under the optimized conditions, the maximum yield and the product e.e. were 89.5% and >99.9%, respectively, in 70 minutes. Compared with the best available data in aqueous system (yield of 55%), the yield of (R)-2-octanol was greatly increased. Additionally, the efficient whole-cell biocatalytic process was feasible on a 200-mL preparative scale and the chemical yield increased to 95.0% with the product e.e. being >99.9%. Moreover, Acetobacter pasteurianus GIM1.158 cells were proved to be capable of catalyzing the anti-Prelog bioreduction of other prochiral carbonyl compounds with high efficiency.

Conclusions

Via an effective increase in the maximum yield and the product e.e. with Acetobacter pasteurianus GIM1.158 cells, these results open the way to use of whole cells of this microorganism for challenging enantioselective reduction reactions on laboratory and commercial scales.

Efficient biocatalytic synthesis of (R)-[3,5-bis(trifluoromethyl)phenyl] ethanol by a newly isolated Trichoderma asperellum ZJPH0810 using dual cosubstrate: ethanol and glycerol

(R)-[3,5-bis(trifluoromethyl)phenyl] ethanol is a crucial intermediate for the synthesis of Aprepitant. An efficient biocatalytic process for (R)-[3,5-bis(trifluoromethyl)phenyl] ethanol was developed via the asymmetric reduction of 3,5-bis(trifluoromethyl) acetophenone, catalyzed by whole cells of newly isolated Trichoderma asperellum ZJPH0810 using ethanol and glycerol as dual cosubstrate for cofactor recycling. A fungal strain ZJPH0810, showing asymmetric biocatalytic activity of 3,5-bis(trifluoromethyl) acetophenone to its corresponding (R)-[3,5-bis(trifluoromethyl)phenyl] ethanol, was isolated from a soil sample. Based on its morphological and physiological characteristics and internal transcribed spacer sequence, this isolate was identified as T. asperellum ZJPH0810, which afforded an NADH-dependent (R)-stereospecific carbonyl reductase and was a promising biocatalyst for the synthesis of (R)-[3,5-bis(trifluoromethyl)phenyl] ethanol. Some key reaction parameters involved in the bioreduction catalyzed by T. asperellum ZJPH0810 were subsequently optimized. The effectiveness of (R)-[3,5-bis(trifluoromethyl)phenyl] ethanol production was significantly enhanced by employing a novel dual cosubstrate-coupled system for cofactor recycling. The established efficient bioreduction system contained 50 mM of 3,5-bis(trifluoromethyl) acetophenone and 60 g l(-1) of resting cells, employing ethanol (6.0 %, v/v) and glycerol (0.5 %, v/v) as dual cosubstrate. The bioreduction was performed in distilled water medium, at 30 °C and 200 rpm. Under the above conditions, a best yield of 93.4 % was obtained, which is nearly a 3.5-fold increase in contrast to no addition of cosubstrate. The ee value of the product reached above 98 %. This biocatalytic process shows great potential in the production of (R)-[3,5-bis(trifluoromethyl)phenyl] ethanol, a valuable chiral building block in the pharmaceutical industry.

Response surface methodology as optimization strategy for asymmetric bioreduction of (4S)-(+)-carvone by Cryptococcus gastricus

Response surface methodology was applied in optimizing the asymmetric bioreduction of (4S)-(+)-carvone to dihydrocarvone (with low incidence of unsought side reactions) by using whole-cells of Cryptococcus gastricus. A factorial design (2(5)) including five independent variables was performed: X(1)=incubation time; X(2)=pH; X(3)=amount of whole-cells; X(4)=concentration of (4S)-(+)-carvone; X(5)=concentration of cofactor-recycling system. The utilization of glucose and glycerol as cofactor-recycling systems was checked. On the basis of the results of factorial design, three independent variables (X(1), X(3) and X(4)) out of five were further selected for performing a central composite design (CCD). First and second order polynomial equations obtained by CCD were used to select the optimal values of independent variables in order to maximize the bioreduction yield of (4S)-(+)-carvone and, at the same time, to minimize the occurrence of side reactions (i.e. further reduction of dihydrocarvone to dihydrocarveol).

Immobilization of Acetobacter sp. CCTCC M209061 for efficient asymmetric reduction of ketones and biocatalyst recycling

Background

The bacterium Acetobacter sp. CCTCC M209061 is a promising whole-cell biocatalyst with exclusive anti-Prelog stereoselectivity for the reduction of prochiral ketones that can be used to make valuable chiral alcohols such as (R)-4-(trimethylsilyl)-3-butyn-2-ol. Although it has promising catalytic properties, its stability and reusability are relatively poor compared to other biocatalysts. Hence, we explored various materials for immobilizing the active cells, in order to improve the operational stability of biocatalyst.

Results

It was found that Ca-alginate give the best immobilized biocatalyst, which was then coated with chitosan to further improve its mechanical strength and swelling-resistance properties. Conditions were optimized for formation of reusable immobilized beads which can be used for repeated batch asymmetric reduction of 4′-chloroacetophenone. The optimized immobilized biocatalyst was very promising, with a specific activity of 85% that of the free-cell biocatalyst (34.66 μmol/min/g dw of cells for immobilized catalyst vs 40.54 μmol/min/g for free cells in the asymmetric reduction of 4′-chloroacetophenone). The immobilized cells showed better thermal stability, pH stability, solvent tolerance and storability compared with free cells. After 25 cycles reaction, the immobilized beads still retained >50% catalytic activity, which was 3.5 times higher than degree of retention of activity by free cells reused in a similar way. The cells could be recultured in the beads to regain full activity and perform a further 25 cycles of the reduction reaction. The external mass transfer resistances were negligible as deduced from Damkohler modulus Da < <1, and internal mass transfer restriction affected the reduction action but was not the principal rate-controlling step according to effectiveness factors η < 1 and Thiele modulus 0.3<∅ <1.

Conclusions

Ca-alginate coated with chitosan is a highly effective material for immobilization of Acetobacter sp. CCTCC M209061 cells for repeated use in the asymmetric reduction of ketones. Only a small cost in terms of the slightly lower catalytic activity compared to free cells could give highly practicable immobilized biocatalyst.

Xylitol production from corncob hydrolysate using polyurethane foam with immobilized Candida tropicalis

Polyurethane foam (PUF) was used as a carrier for Candida tropicalis (C. tropicalis) in the multi-batches fermentation of xylitol from xylose-containing corncob hemicellulose hydrolysate. After washing and sterilization, PUF (density of 320 kgm(-3), specific surface area of 1.5-2.0 × 10(5) m(2) m(-3), average porosity of 95%, pore diameter of 0.03 mm and cubic length of 5mm) was mixed with the culture medium at appropriate proportion followed by the inoculation. The fermentation parameters such as initial cell concentration, PUF dosage, pH value and temperature were controlled to study the effects on xylitol fermentation. In the 21-day durability tests, the optimal xylitol yield and volumetric productivity reached to 71.2% and 2.10 gL(-1)h(-1) respectively. Moreover, the average xylitol yield and volumetric productivity were 66.3% and 1.90 gL(-1)h(-1) for ten batchwise operations. The current research demonstrated that the PUF immobilization could serve as an efficient method for improving the cells vitality and enzyme reactivity in the continuous operation of fermentation.

Diplogelasinospora grovesii IMI 171018 immobilized in polyurethane foam. An efficient biocatalyst for stereoselective reduction of ketones

Diplogelasinospora grovesii has been reported as a very active biocatalyst in the reduction of ketones. Along the text, the properties of this filamentous fungus as an immobilized catalyst are described. For this purpose, several immobilization supports as agar and polyurethane foam were tested. Experimental assays were also performed to test different co-substrates for the regeneration of the required enzyme cofactor. The fungus immobilized in polyurethane foam lead to the most stable and active catalyst. This derivative, using i-PrOH as co-substrate, could be reused at least 18 times without appreciable activity loss (>90% activity remains). Kinetic runs experiments shown that the reduction of cyclohexanone, selected as model substrate, followed a pseudo-first kinetic order and that the rate controlling step was the mass transfer through the cell wall. The deactivation kinetic constants were also determined. The reduction of different chiral ketones showed that the ketone reductase activity followed the Prelog's rule.

Pentachlorophenol sorption in nylon fiber and removal by immobilized Rhizopus oryzae ENHE

This study describes pentachlophenol (PCP) sorption in nylon fiber in which Rhizopus oryzae ENHE was immobilized to remove the chemical compound. The experimental sorption data were analyzed using the Langmuir, Freundlich, and Redlich-Peterson isotherm models using non-linear error functions to fit the experimental data to the three models. Results showed that the isotherm obtained from the data fitted the three models used. However, the g parameter from Redlich-Peterson model showed that the isotherm obtained approaches the Freundlich model. This support reached the sorption equilibrium concentration at 3mg PCPg(-1)nylon. To study PCP removal capability by R. oryzae ENHE and to eliminate the error caused by PCP sorbed by the nylon fiber during its quantification, nylon fiber at PCP equilibrium sorption concentration was used to immobilize R. oryzae ENHE. It was found that this fungus grew within nylon fiber cubes in presence or not of PCP, even when PCP caused growth inhibition. Maximum biomass accumulated into nylon cubes without PCP was of 32 mg biomass g(-1)nylon and into nylon cubes at PCP equilibrium concentration was of 18 mg g(-1)nylon. The results showed that R. oryzae ENHE immobilized into nylon fiber removed 88.6% and 92% of PCP in cultures with 12.5 and 25 mg PCPL(-1), as initial concentration, respectively. This is the first work to report that a zygomycete, such as R. oryzae ENHE, immobilized into nylon fiber kept its potential to remove PCP.

Bioreduction of α,β-unsaturated ketones and aldehydes by non-conventional yeast (NCY) whole-cells

The bioreduction of α,β-unsaturated ketones (ketoisophorone, 2-methyl- and 3-methyl-cyclopentenone) and aldehydes [(S)-(-)-perillaldehyde and α-methyl-cinnamaldehyde] by 23 "non-conventional" yeasts (NCYs) belonging to 21 species of the genera Candida, Cryptococcus, Debaryomyces, Hanseniaspora, Kazachstania, Kluyveromyces, Lindnera, Nakaseomyces, Vanderwaltozyma, and Wickerhamomyces was reported. The results highlight the potential of NCYs as whole-cell biocatalysts for selective biotransformation of electron-poor alkenes. A few NCYs exhibited extremely high (>90%) or even total ketoisophorone and 2-methyl-cyclopentenone bioconversion yields via asymmetric reduction of the conjugated CC bond catalyzed by enoate reductases. Catalytic efficiency declined after switching from ketones to aldehydes. High chemoselectivity due to low competing carbonyl reductases was also sometimes observed.

Highly enantioselective reduction of 2-hydroxy-1-phenylethanone to enantiopure (R)-phenyl-1,2-ethanediol using Saccharomyces cerevisiae of remarkable reaction stability

Saccharomyces cerevisiae JUC15 was successfully obtained by target reaction-oriented screening, which reduced 2-hydroxy-1-phenylethanone (HPE) to (R)-phenyl-1,2-ethanediol ((R)-PED) of excellent enantiomeric excess (e.e. >99.9%). There was no significant decrease in the yield and optical purity of (R)-PED when the free cells were reused for 40 repeated cycles at 2gL(-1) substrate concentration. The strain used cheap sucrose for cofactor regeneration and worked over a considerably wider range of pH (4-9). The optimum substrate concentration was 8gL(-1), which was higher than any other biocatalysts reported so far. Interesting, when HPE concentration reached 20gL(-1) in reaction system, where 43.2% of the substrate was present in suspended solid form, the reaction still gave enantiopure (R)-PED in 71% yield. Last but not least, the product e.e. kept above 99.9% in all examined conditions. These results suggest the potential of this strain for the industrial production of optically active (R)-PED.

Exploring threshold operation criteria of biostimulation for azo dye decolorization using immobilized cell systems

This follow-up study provided an evaluation on threshold operation criteria of biostimulation in immobilized cell systems (ICSs) with Aeromonas hydrophila onto packing materials Porites corals. Essential nutrients in appropriate flow rate for biostimulation were inevitably required to maintain maximum attached cell population for cost-effective biodecolorization. With the method of "graphical reconstruction", the most economically feasible strategy of medium stimulation for color removal was quantitatively revealed. Our findings pointed out no matter what operation mode of reactor was (e.g., suspended batch cultures or ICS) color removal efficiency for A. hydrophila still strongly depended upon intrinsic kinetics and chemical reactivities of azo dyes. Mass transport effects in ICS might not play most significant roles to limit dye biodecolorization of A. hydrophila (except Reactive red 198, Reactive green 19), as relative rankings of color removal rates of various dyes were almost in parallel with those in suspended batch cultures.

Cost-effective biostimulation strategy for wastewater decolorization using immobilized-cell systems

This study tended to evaluate threshold operation criteria of biostimulation for optimal biodecolorization in immobilized-cell systems (ICSs) using Porites corals as packing matrices. Indigenous Aeromonas hydrophila with high efficiency for decolorization isolated from Northeast Taiwan was used for study. As maximal treatment performance of ICS could only be achieved with maximal absorbed biomass with highest color removal capability. Maintaining optimal attached cells for cost-effective color removal efficiency inevitably required essential nutrients provided from rich media for biostimulation. With consideration of efficient cell attachment and maximal dye biodecolorization, our proposed method of "graphical reconstruction" quantitatively revealed the most economically-feasible strategy of medium stimulation for color removal. Our findings pointed out the maximal allowable inlet concentration and treatment capacity using our prediction of constant-slope isoclines of ICSs at cultures fed with different concentrations of nutrient sources. The method of isoclines upon transient dynamics of ICSs also provided a technically viable assessment for on-site professionals to quantitatively determine maximal biotreatment thresholds in biostimulation.