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Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.134, #3)

Biosorption of radioactive thorium by Sargassum filipendula by Marta Cristina Picardo; Ana Cristina de Melo Ferreira; Antonio Carlos Augusto da Costa (pp. 193-206).

In the present work, the biosorption of radioactive thorium was investigated using a dry biomass of Sargassum filipendula as the biosorbent material. Radioactive solutions containing between 2.0 and 500.0μg thorium were tested by biosorption with S. filipendula, yielding uptake capacities from 20 to 100%, depending on the concentration of the solution. Kinetic studies indicated that equilibrium between the thorium solution and the solid fraction was achieved after three hours of contact and that a second-order model could express the equilibrium kinetics. In order to investigate the maximum biosorption capacity of the biomass an isotherm was done, based on the experimental data, which revealed the maximum uptake capacity to be 2.59 μmol thorium/g biomass. The experimental data fitted well to a Langmuir model, which provided a good correlation between the experimental and predicted thorium uptake values.

Keywords: Sargassum filipendula ; thorium; wastewater; biosorption; kinetic models

A new method for microcapsule characterization by Hongmei Chen; Wei Ouyang; Bisi Lawuyi; Trisna Lim; Satya Prakash (pp. 207-221).

Numerous microcapsule systems have been developed for a wide range of applications, including the sustained release of drugs, cell transplantation for therapy, cell immobilization, and other biotechnological applications. Despite the fact that microcapsule membrane is a dominant factor governing overall microcapsule performance, its characterization is challenging. We report a new method for characterizing microcapsule membranes, using the most common alginate-poly-l-lysine-alginate (APA) microcapsule as an example. Our data demonstrate that genipin, a naturally derived reagent extracted from gardenia fruits, interacts with poly-l-lysine (PLL) and generates fluorescence. This fluorescence allows clear visualization and easy analysis of the PLL membrane in the APA microcapsules using confocal laser scanning microscopy. The results also show that PLL binding correlates to the reaction variables during PLL coating such as PLL concentration and coating time. In addition, five other different microcapsule formulations consisting of PLL and/or chitosan membranes were examined, and the results imply that this method can be extended to characterize a variety of microcapsule membranes. These findings suggest that genipin can serve as a fluorogenic marker for rapid characterization of microcapsule membranes, a superior method that would have important implications for microcapsule research and potential in many other applications.

Keywords: Microcapsule; poly-l-lysine; alginate-poly-l-lysine-alginate; genipin; chitosan; fluorescence; confocal laser scanning microscopy

Lactic acid bacteria production from whey by María Elena Mondragón-Parada; Minerva Nájera-Martínez; Cleotilde Juárez-Ramírez; Juvencio Galíndez-Mayer; Nora Ruiz-Ordaz; Eliseo Cristiani-Urbina (pp. 223-232).

The main purpose of this work was to isolate and characterize lactic acid bacteria (LAB) strains to be used for biomass production using a whey-based medium supplemented with an ammonium salt and with very low levels of yeast extract (0.25 g/L). Five strains of LAB were isolated from naturally soured milk after enrichment in whey-based medium. One bacterial isolate, designated MNM2, exhibited a remarkable capability to utilize whey lactose and give a high biomass yield on lactose. This strain was identified as Lactobacillus casei by its 16S rDNA sequence. A kinetic study of cell growth, lactose consumption, and titratable acidity production of this bacterial strain was performed in a bioreactor. The biomass yield on lactose, the percentage of lactose consumption, and the maximum increase in cell mass obtained in the bioreactor were 0.165 g of biomass/g of lactose, 100%, and 2.0 g/L, respectively, which were 1.44,1.11, and 2.35 times higher than those found in flask cultures. The results suggest that it is possible to produce LAB biomass from a whey-based medium supplemented with minimal amounts of yeast extract.

Keywords: Ammonium salts; biomass; lactic acid bacteria; whey; yeast extract

Optimization and modeling of laccase production by Trametes versicolor in a bioreactor using statistical experimental design by A. P. M. Tavares; M. A. Z. Coelho; M. S. M. Agapito; J. A. P. Coutinho; A. M. R. B. Xavier (pp. 233-248).

Experimental design and response surface methodologies were applied to optimize laccase production by Trametes versicolor in a bioreactor. The effects of three factors, initial glucose concentration (0 and 9 g/L), agitation (100 and 180 rpm), and pH (3.0 and 5.0), were evaluated to identify the significant effects and its interactions in the laccase production. The pH of the medium was found to be the most important factor, followed by initial glucose concentration and the interaction of both factors. Agitation did not seem to play an important role in laccase production, nor did the interaction agitation x medium pH and agitation x initial glucose concentration. Response surface analysis showed that an initial glucose concentration of 11 g/L and pH controlled at 5.2 were the optimal conditions for laccase production by T. versicolor. Under these conditions, the predicted value for laccase activity was >10,000 U/L, which is in good agreement with the laccase activity obtained experimentally (11,403 U/L). In addition, a mathematical model for the bioprocess was developed. It is shown that it provides a good description of the experimental profile observed, and that it is capable of predicting biomass growth based on secondary process variables.

Keywords: Bioreactor; enzyme production; kinetic parameters; modeling; optimization; Trametes versicolor

Culture pH affects exopolysaccharide production in submerged mycelial culture of Ganoderma lucidum by Hyun Mi Kim; Moon Ki Park; Jong Won Yun (pp. 249-262).

In submerged culture of Ganoderma lucidum, the pH optimum for cell growth has been shown to be lower than that for exopolysaccharides (EPS) formation. Therefore, in the present study, a two-stage pH-control strategy was employed to maximize the productions of mycelial biomass and EPS. When compared, a batch culture without pH control had a maximum concentration of EPS and endopolysaccharides, which was much lower than those with pH control. Maximum mycelial growth (12.5 g/L) and EPS production (4.7 g/L) were achieved by shifting the controlled pH from 3.0 to 6.0 after day 4. The contrast between the controlled-pH process and uncontrolled pH was marked. By using various two-stage culture processes, it was also observed that culture pH has a significant affect on the yield of product, mycelial morphology, chemical composition, and molecular weight of EPS. A detailed observation of mycelial morphology revealed that the productive morphological form for EPS production was a dispersed pellet (controlled pH shifting from 3.0 to 6.0) rather than a compact pellet with a dense core area (controlled pH 4.5) or a feather-like pellet (controlled pH shifting from 6.0 to 3.0). Three different polysaccharides were obtained from each pH conditions, and their molecular weights and chemical compositions were significantly different.

Keywords: Culture pH; exopolysaccharides; Ganoderma lucidum ; mushrooms; submerged culture

Simultaneous saccharification and fermentation of cassava bagasse for l-(+)-lactic acid production using Lactobacilli by Rojan P. John; K. Madhavan Nampoothiri; Ashok Pandey (pp. 263-272).

Saccharification and fermentation of cassava (Manihot esculenta) bagasse was carried out in a single step for the production of L-(+)-lactic acid by Lactobacillus casei and Lactobacillus delbrueckii. Using 15.5% w/v of cassava bagasse as the raw material, a maximum starch to lactic acid conversion of 96% was obtained with L. casei with a productivity rate of 1.40mg/mL·h and maximum yield of 83.8 mg/mL. It was 94% with L. delbrueckii with a productivity rate of 1.36 mg/mL·h. and maximum yeild of 81.9 mg/mL. Supplementation of bagasse with 0.01% w/v MnCl₂ showed positive influence on the lactic acid production by L. casei.

Keywords: Cassavabagasse; L-(+)-lacticacid; lactobacilli ; simultaneous saccharification; fermentation

Ethanol production from dilute-acid softwood hydrolysate by co-culture by Mingyu Qian; Shen Tian; Xuefeng Li; Jing Zhang; Yaping Pan; Xiushan Yang (pp. 273-283).

Dilute-acid softwood hydrolysate, with glucose and xylose as the dominant sugars was fermented to ethanol by co-cultures. The strains used include Saccharomyces cerevisiae 2.535 (1#), Pachysolen tannophilis ATCC 2.1662 (2#), and recombinant Escherichia coli (3#) constructed in our laboratory carrying both pdc and adhB genes derived from Zymomonas mobilis. Before fermentation, the co-cultures were adapted for five batches. Observation under light microscope showed aggregation of adapted strains, which could possibly improve their ability to degrade inhibitors. In addition, we tried to detoxify the dilute-acid softwood hydrolysate with a combined method before fermentation. Our study showed that fermentation of detoxified hydrolysate by adapted co-culture (1# + 2@) generated an exceptionally high ethanol yield on total sugar of 0.49 g/g, corresponding to 96.1% of the maximal theoretical value after 48h; fermentation of detoxified hydrolysate by adapted co-culture (1# + 3#) is faster (24h) and could reach a high ethanol yield (0.45 g/g total sugar). These experiments suggest that both adaptation and detoxification significantly improve hydrolysate fermentation and ethanol production.

Keywords: Dilute-acid softwood hydrolysate; co-cultures; strain adaptation; batch fermentation; ethanol fermentation

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Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.134, #3)

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Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.134, #3)