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Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.82, #2)
Exopolysaccharide production by a marine cyanobacterium Cyanothece sp. by Vishal Shah; Nikki Garg; Datta Madamwar (pp. 81-90).
Cyanobacterium Cyanothece sp. ATCC 51142 has been shown to produce an exopolysaccharide (EPS) at a high level. EPS production was found to be influenced by the concentration of salt, pH, and type of nitrogen source. Maximum polysaccharide production was found to occur at a 4.5% (w/v) NaCl salt concentration, pH 7.0, and in the presence of NaNO3 as the nitrogen source. The gelation of EPS in alkaline conditions was employed to remove the dyes from the effluents. The effect of organic molecules and metal ions on the efficiency of dye removal capacity was investigated. A laboratory-scale reactor was prepared to treat artificial textile effluent.
Keywords: Cyanothece ; cyanobacterium; dyes; exopolysaccharide; gelation; wastewater treatment
Influence of redox potential on product distribution in Clostridium thermosuccinogenes by Jayanth Sridhar; Mark A. Eiteman (pp. 91-101).
Clostridium thermosuccinogenes are the only known anaerobic thermophilic bacteria that ferment inulin to succinate and acetate as major products and formate, lactate, and ethanol as minor products. In this study, organic acid production in 2-L fermentations having an initially low (−300 to −330 mV) or high (−220 to −250 mV) redox potential was compared for two strains of C. thermosuccinogenes (DSM 5808 and DSM 5809). Although DSM 5809 consistently provided higher succinate yield, high variability in results was attributed to the absence of redox control during the fermentations, and, therefore, fermentations at three controlled redox potentials (−240, −275, and −310 mV) were conducted. At an intermediate redox potential (−275 mV), the succinate yield was the greatest (0.36 g of succinate/g of hexose unit), whereas ethanol yield was the least (0.02 g/g). Redox potential did not significantly affect acetate or lactate formation. At controlled redox potential of −275 mV, the growth of DSM 5809 on three substrates was also compared: inulin, fructose, and glucose. DSM 5809 had similar growth rates when inulin (0.20/h) or glucose (0.21/h) was the carbon source but grew more slowly when fructose (0.16/h) was the carbon source. Also, the specific rate of utilization of fructose by DSM 5809 was higher (0.89 g of fructose/[g of biomass·h]) compared to glucose (0.53 g/[g·h]) or inulin (0.55 g/[g·h]). Succinate was the major product formed by DSM 5809 fermenting inulin (0.50 g/[g·h]) or glucose (0.36 g/[g·h]), and ethanol was the principal product when DSM 5809 fermented fructose (0.54 g/[g·h]).
Keywords: Clostridium thermosuccinogenes ; inulin; succinic acid; anaerobic fermentation; thermophile
Inulinase synthesis from a mesophilic culture in submerged cultivation by Ashok Pandey; Simon Joseph; L. Ashakumary; P. Selvakumar; Carlos R. Soccol (pp. 103-114).
A newly isolated mesophilic bacterial strain from dahlia rhizosphere, identified as Staphylococcus sp. and designated as RRL-M-5, was evaluated for inulinase synthesis in submerged cultivation using different carbon sources individually or in combination with inulin as substrate. Inulin appeared as the most favorable substrate at a 0.5–1.0% concentration. Media pH influenced the enzyme synthesis by the bacterial strain, which showed an optimum pH at 7.0–7.5. Supplementation of fermentation medium with external nitrogen (organic and inorganic) showed a mixed impact on bacterial activity of enzyme synthesis. The addition of soybean meal and corn steep solid resulted in about an 11% increase in enzyme titers. Among inorganic nitrogen sources, ammonium sulfate was found to be the most suitable. Maximum enzyme activities (446 U/L) were obtained when fermentation was carried out at 30°C for 24 h with a medium containing 0.5% inulin as a sole carbon source and 0.5% soybean meal as the nitrogen source. Bacterial inulinase could be a good source for the hydrolysis of inulin for the production of d-fructose.
Keywords: Inulinase; mesophilic bacteria; inulin; submerged fermentation; carbon and nitrogen sources
Influence of some amino acids on the dynamic swelling behavior of radiation-induced acrylamide hydrogel by Dursun Saraydin; H. Nursevin Öztop; Erdener Karadag; Yasemin Çaldiran; Olgun Güven (pp. 115-125).
The influence of some amino acids—alanine, glycine, valine, glutamine, histidine, phenylalanine, and tryptophan—on the swelling behavior of acrylamide (AAm) hydrogel prepared by γ-radiation was investigated. Swelling experiments of AAm hydrogel were made in the universal buffer solutions and the amino acid solutions at certain pHs at 37°C. These selected pH values were pK1, pK2 and isoelectric point (pI) values such as ionization of α-carboxyl groups, ionization of α-amino groups, and the pIs of the amino acids, respectively. The swelling of AAm hydrogel increased when pH values of solutions were increased. The value of equilibrium swelling of AAm hydrogel in the solution of universal buffer was 880% at pH 10.0, whereas it was 670% at pH 2.0. The values of equilibrium swelling of AAm hydrogel in amino acid solutions were between 830 and 965% at pH 10.0, whereas they were between 635 and 775% at pH 2.0. The rate constant of swelling, initial swelling rate, theoretical maximum swelling, diffusional exponent, network parameter, and diffusion coefficient were calculated by swelling kinetics. Diffusions of the amino acid solutions into the hydrogel were generally found as non-Fickian in character. The diffusion coefficients of the hydrogel were between 0.91 × 10−6 and 2.41 × 10−6 cm2/s.
Keywords: Amino acid; hydrogel; acrylamide; swelling; diffusion
The influence of inert solids on ethanol production by Saccharomyces cerevisiae by R. S. Prakasham; Boney Kuriakose; S. V. Ramakrishna (pp. 127-134).
The catalytic role of various inert solid supports on acceleration of alcohol fermentation by Saccharomyces cerevisiae was investigated. The enhanced rate of alcohol production was dependent on the nature of the support as well as on the amount used. Among all the tested supports, chitosan flakes showed the maximum yield of alcohol (93% of theoretical yield). This higher rate of alcohol production was associated with the twofold increase in the activity of alcohol dehydrogenase over control. Our results suggest that the addition of a small fraction of solids in submerged fermentations to facilitate cell anchorage for enhanced metabolic activity is easier and more economical compared to cell immobilization processes.
Keywords: Alcoholdehydrogenase; ethanol; chitin; chitosan; river sand; sawdust; wheat bran; Saccharomyces cerevisiae
Purification of carbohydrate-containing substrates from plant biomass hydrolysates by Yuri I. Kholkin; Vladimir V. Viglazov; Vladimir B. Kind; Howard D. Mettee (pp. 135-140).
Carbohydrate-containing substrates are produced in Russia by means of dilute acid hydrolysis of wood and vegetable residues. Hydrolysates contain 3 to 4% monosaccharides and nearly 1% impurities. The common schemes used to prepare the hydrolysate for fermentation include cooling by self-evaporation; inversion of oligosaccharides; neutralization of sulfuric (and organic) acids; addition of mineral food substances containing nutrient N, P, and K salts; aeration to coagulate colloidal substances; and sedimentation of residues. Our work led to the suggestion that a flocculation step using cationic polyelectrolytes be added to purify more completely the substrates from lignin-huminic substances (LHS). This method permits the transfer of a part of the dissolved and colloidal LHS into a suspended state and the removal of more than 90% of the suspended materials, thereby increasing the yield and quality of ethanol and fodder yeast. Three industrial plants have reported successful results using this method in the past few years. Flocculation has also proven itself capable of clearing waste culture liquids of their dispersed phases by extents of 30–60%, as measured by chemical oxygen demand, color depth, or lignin content parameters, prior to consideration of such wastewater for recycling.
Keywords: Flocculation; vegetable hydrolysates; cationic polymers; purification
Xylitol production from hardwood hemicellulose hydrolysates by Pachysolen tannophilus, Debaryomyces hansenii, and Candida guilliermondii by Attilio Converti; Patrizia Perego; José Manuel Domínguez (pp. 141-151).
Three different yeasts, Pachysolen tannophilus, Debaryomyces hansenii, and Candida guilliermondii, were evaluated to ferment xylose solutions prepared from hardwood hemicellulose hydrolysates, among which P. tannophilus proved to be the most promising microorganism. However, the presence of both lignin-derived compounds (LDC) and acetic acid rendered a poor fermentation. To enhance the fermentation kinetics, different treatments to purify the hydrolysates were studied, including overliming, charcoal adsorption for LDC removal, and evaporation for acetic acid and furfural stripping. Under the best operating conditions assayed, 39.5g/L of xylitol were achieved after 96 h of fermentation, which corresponds to a volumetric productivity of 0.41 g/L·h and a yield of product on consumed substrate of 0.63 g p /gS.
Keywords: Xylitol; hemicellulose hydrolysate; Debaryomyces hansenii ; Candida guilliermondii ; Pachysolen tannophilus
Enzymes produced by soil fungi following microaerobic growth on lignocellulosic materials by Erika C. Pavarina; Lara D. Sette; Tania A. Anazawa; Lucia R. Durrant (pp. 153-163).
Four fungal strains able to grow under low oxygenation conditions were selected and used in studies to determine the production of enzymes (endoglucanases, exoglucases, β-glucosidase, and peroxidases) that promote the degradation of lignocellulosic materials. The capacity of the fungi to ferment lignocellulosic materials was also investigated. Avicel, xylan, Whatman no. 1 filter paper, or agroindustrial residues were used as carbon sources in a medium containing mineral salts, vitamins, and cysteine as a reducing agent, under either microaerophilic or combined conditions (aerobic followed by microaerophilic conditions). The results obtained with strains Q10, H2, and LH5 suggest that they prefer a low oxygen concentration for growth and enzyme production. However, strain F20 seems to need higher levels of oxygenation. Lignocellulolytic activities were detected in all strains but varied with the carbon source used for growth. In general, the highest levels of these activities were produced by strain H2 under microaerophilic conditions. Ethanol and other nongaseous fermentation products were detected following high-performance liquid chromatography analysis using a Supelcogel C-610H column, demonstrating the fermentative capability of these strains.
Keywords: Cellulolytic fungi; lignocellulases; lignocellulose degradation; xylanases