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Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.128, #2)

Immobilized catalase on CoFoam hydrophilic polyurethane composite by Palligarnai T. Vasudevan; Karin Como (pp. 97-107).

Catalase from bovine liver was covalently immobilized on hydrophilic polyurethane composite (CoFoam). The activity of the enzyme was assayed in the decomposition of H₂O₂ at pH 7.0 and 25°C. The effects of water-to-prepolymer ration the addition of a crosslinking agent, and the utilization of a spacer on enzyme, activity were examined. The results of immobilization of the enzyme in a large-scale unit are reported. The advantage of the CoFoam composite lies in the low drop in pressure in a packed-bed reactor at fairly large flow rates. For example, at flow rates of 10–12 L/min, the drop in pressure is typically 3 kPa. Enzymes immobilized on CoFoam represent a novel use as catalysts in packed-bed reactors owing to the low drop in pressure.

Keywords: CoFoam; catalase; hydrophilic polyurethane

Production of biodiesel by immobilized Candida sp. lipase at high water content by Tianwei Tan; Kaili Nie; Fang Wang (pp. 109-116).

A new process for enzymatic synthesis of biodiesel at high water content (10–20%) with 96% conversion by lipase from Candida sp. 99–125 was studied. The lipase, a no-position-specific lipase, was immobilized by a cheap cotton membrane and the membrane-immobilized lipase could be used at least six times with high conversion. The immobilized lipase could be used for different oil conversion and preferred unsaturated fatty acids such as oleic acid to staturated fatty acids such as palmitic acid. The changes in concentration of fatty acids, diglycerides, and methyl esters in the reaction were studied and a mechanism of synthesis of biodiesel was suggested: the triglycerides are first enzymatically hydrolyzed into fatty acids, and then these fatty acids are further converted into methyl esters.

Keywords: Biodiesel; lipase; Candida sp. lipase; membrane immobilization

Surface modification of neural probes with conducting polymer poly(hydroxymethylated-3,4-ethylenedioxythiophene) and its biocompatibility by Yinghong Xiao; David C. Martin; Xinyan Cui; Mahesh Shenai (pp. 117-129).

A novel conducting polymer, poly(hydroxymethylated-3,4-ethylenedioxy-thiophene) (PEDOT-MeOH), was electrochemically deposited onto the electrodes of micromachined neural probes. Uniformly distributed film was obtained from aqueous solution when doped with polystyrenesulfonate. The surface morphology was rough and had good cellular adhesion. Impedance spectroscopy showed that the magnitude of coated electrode was lower than that of the bare gold over a range of frequencies from 10⁰ to 10⁵ Hz. Since the biocompatibility of the interface between the neural probes and brain tissue plays an important role when the probes are implanted in the central nervous system for long-term application, biomolecules were incorporated into the coating. Nonapeptide CDPGYIGSR was codeposited as the counterion in the conducting films. The surface morphology of the coating was fuzzy, providing many bioactive sites for interaction with neural cells. The magnitude of impedance was as low as 53 kω at the biologically relevant frequency of 1 kHz. An in vitro experiment demonstrated that the neuroblastoma cells grew preferentially on the PEDOT-MeOH/CDPGYIGSR-coated electrode sites and spread beyond the electrode area.

Keywords: Conducting polymer; surface modification; micromachined neural probe; biocompatibility

Optimization of glucoamylase production by Aspergillus niger in solid-state fermentation by Silvana T. Silveira; Melissa S. Oliveira; Jorge A. V. Costa; Susana J. Kalil (pp. 131-139).

Glucoamylase production by Aspergillus niger in solid-state fermentation was optimized using factorial design and response surface techniques. The variables evaluated were pH and bed thickness in tray, having as response enzyme production and productivity. The bed thickness in tray was the most significant variable for both responses. The highest values for glucoamylase production occurred using pH 4.5 and bed thickness in the inferior limits at 2.0–4.2 cm. For productivity, the optimal conditions were at pH 4.5 as well and bed thickness from 4.4 to 7.5 cm. The optimal conditions for glucoamylase production while obtaining high activity without loss of productivity were pH 4.5 and bed thickness in tray from 4.0 to 4.5 cm, which resulted in an enzyme production of 695 U/g and productivity of 5791 U/h.

Keywords: Aspergillus niger, factorial design; glucoamylase; optimization; solid-state fermentation

Biodegradation of biomass gasification wastewater by two species of Pseudomonas using immobilized cell reactor by Shen Tian; Cheng Qian; Xiushan Yang (pp. 141-147).

An immobilized cell bioreactor with granular activated carbon as the inert material inoculated two species, Pseudomonas sp1 and Pseudomonas sp2, to degrade chemical oxygen demand (COD) and benzene, naphthalene, phenanthrene, pyridine, quinoline, and isoquinoline in the wastewater discharging from a biomass gasification power-generation plant. The results indicated that these toxic compounds were removed efficiently. The course of the 66-d experiment was divided into three phases mainly in accordance with different influent COD concentrations: microbial adaptation and proliferation phase (from 1 to 23 d), stable metabolic phase (from 24 to 57 d), and high efficient reaction phase (from 58 to 66 d). The high removal rates of COD and some toxic compounds with a 24-h hydraulic retention time were accomplished.

Keywords: Biomass gasification wastewater; Pseudomonas species; granular activated carbon; immobilized cells; chemical oxygen demand; toxic compound removal

A soluble form of phosphatase in Saccharomyces cerevisiae capable of converting farnesyl diphosphate into E,E-farnesol by Linsheng Song (pp. 149-157).

After anion-exchange chromatography, the soluble fraction of a cell-free extract of Saccharomyces cerevisiae showed two phosphatase activity peaks when p-nitrophenyl phosphate (pNPP) was used as the substrate. However, only the second pNPP active peak demonstrated the ability to convert farnesyl diphosphate (FPP) into E,E-farnesol. N-terminal sequence analysis of the purified pNPP/FPP phosphatase revealed that it was a truncated form of alkaline phosphatase Pho8 lacking 62 amino acids from the N-terminus and was designated Pho8Δ62. Although other isoprenyl diphosphates such as geranyl diphosphate (GPP) and geranylgeranyl diphosphate (GGPP) could also be hydrolyzed by Pho8Δ62 to the corresponding alcohols, selectivity was observed among these substrates. The optimum pH was 7.0 for all three isoprenyl diphosphate substrates. Although lower hydrolytic activity was observed for FPP and GGPP at pH 6.0 and 8.5, hydrolysis of GPP was observed only at pH 7.0. Mg²⁺ and Mn²⁺ inhibited hydrolysis of FPP and GGPP, and GGPP was more sensitive to Mg²⁺ inhibition than FPP. The rate of FPP hydrolysis increased in the presence of Triton X-100.

Keywords: Phosphatase; farnesyl diphosphate; isoprenoid; farnesol

Biobleaching of nonwoody pulps using xylanase of Bacillus brevis BISR-062 by B. Choudhury; Preetika Aggarwal; R. K. Gothwal; Rahul Mantri; M. K. Mohan; P. Ghosh (pp. 159-169).

The efficiency of xylanase of Bacillus brevis BISR-062 as a prebleaching agent was evaluated on three nonwoody pulps at two different pH values (7.0 and 8.5). Crude xylanase was found to have an optimum temperature and pH of 65–70°C and 7.0, respectively. The stability of the enzyme was determined at two pH values (7.0 and 8.0), and it lost approx 50% of its activity at both values within 2 h at 50°C. However, the enzyme was found to be effective as a prebleaching agent only with rice straw pulp. A maximum brightness gain of 6 points was obtained with this pulp at pH 7.0. The strength properties of the rice straw pulp at pH 7.0 also improved as the result of enzyme treatment.

Keywords: Biobleaching; Bacillus brevis ; xylanase; nonwoody pulps

Lactic acid fermentation in cell-recycle membrane bioreactor by B. Choudhury; T. Swaminathan (pp. 171-183).

Traditional lactic acid fermentation suffers from low productivity and low product purity. Cell-recycle fermentation has become one of the methods to obtain high cell density, which results in higher productivity. Lactic acid fermentation was investigated in a cell-recycle membrane bioreactor at higher substrate concentrations of 100 and 120 g/dm³. A maximum cell density of 145 g/dm³ and a maximum productivity of 34 g/(dm³…h) were achieved in cell-recycle fermentation. In spite of complete consumption of substrate, there was a continuous increase in cell density in cell-recycle fermentation. Control of cell density in cell-recycle fermentation was attempted by cell bleeding and reduction in yeast extract concentration.

Keywords: Lactic acid fermentation; cell-recycle reactor; membrane bioreactor; cell bleeding; continuous fermentation; high cell density

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Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.128, #2)

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Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.128, #2)