Lignin peroxidase from Streptomyces viridosporus T7A: enzyme concentration using ultrafiltration.

It is well known that lignin degradation is a key step in the natural process of biomass decay whereby oxidative enzymes such as laccases and high redox potential ligninolytic peroxidases and oxidases play a central role. More recently, the importance of these enzymes has increased because of their prospective industrial use for the degradation of the biomass lignin to increase the accessibility of the cellulose and hemicellulose moieties to be used as renewable material for the production of fuels and chemicals. These biocatalysts also present potential application on environmental biocatalysis for the degradation of xenobiotics and recalcitrant pollutants. However, the cost for these enzymes production, separation, and concentration must be low to permit its industrial use. This work studied the concentration of lignin peroxidase (LiP), produced by Streptomyces viridosporus T7A, by ultrafiltration, in a laboratory-stirred cell, loaded with polysulfone (PS) or cellulose acetate (CA) membranes with molecular weight cutoffs (MWCO) of 10, 20, and 50 KDa. Experiments were carried out at 25 degrees C and pH 7.0 in accordance to the enzyme stability profile. The best process conditions and enzyme yield were obtained using a PS membrane with 10 KDa MWCO, whereby it was observed a tenfold LiP activity increase, reaching 1,000 U/L and 90% enzyme activity upholding.

Optimizing the operational conditions of a membrane bioreactor used for domestic wastewater treatment

Biorreatores com membrana para retenção de sólidos consistem em processos biológicos acoplados a módulos de membranas de microfiltração ou ultrafiltração. O presente estudo avaliou o desempenho de um módulo de membranas, combinado a um sistema de aeração, para o tratamento de esgoto doméstico. Com o objetivo de investigar o comportamento das membranas e minimizar os efeitos do "fouling", foram realizados testes em unidades em escala de laboratório, nos quais foram estabelecidos valores ótimos para alguns parâmetros operacionais, como velocidade tangencial no módulo, pressão transmembrana e vazão de ar inserida na linha de alimentação do módulo. Com a inserção de ar foi possível controlar melhor o comportamento do fluxo permeado ao longo do tempo. Após seis horas de operação, o fluxo se manteve em torno de 35 L/m2.h para uma pressão total de 0,40 bar (pressão gerada pelo esgoto de 0,05bar e pelo ar de 0,35 bar) e Reynolds de 4.600. Todas as análises das amostras do permeado indicaram ausência de coliformes termotolerantes e Escherichia coli.

Effect of aeration on lignin peroxidase production by Streptomyces viridosporus T7A.

The effect of aeration on lignin peroxidase production by Streptomyces viridosporus T7A was studied in a bench-scale bioreactor using a previously optimized growth medium (0.65% yeast extract and 0.1% corn oil, pH 7.0) at 37 degrees C and natural pH. Airflow rates of 0.3, 1.0, and 1.5 vvm and a fixed agitation of 200 rpm were initially studied followed by 1.0 vvm and 200, 300, 400, and 500 rpm. The use of 1.0 vvm and 400 rpm increased enzyme concentration 1.8-fold (100-180 U/L) and process productivity 4.8-fold (1.4-6.7 U/[L h]) in comparison with the use of 200 rpm and 0.3 vvm. The inexpensive corn oil, used as carbon source, besides its antifoam properties, proved to be nonrepressive for enzyme production.

Influence of oxygen availability on cell growth and xylitol production by Candida guilliermondii.

Oxygen availability is the most important environmental parameter in the production of xylitol by yeasts, directly affecting yields and volumetric productivity. This work evaluated the cell behavior in fermentations carried out with different dissolved oxygen concentrations (0.5-30.0% of saturation), as well as a limited oxygen restriction (0% of saturation), at several oxygen volumetric transfer coefficients (12 < or = kLa < or = 70 h(-1)). These experiments allowed us to establish the specific oxygen uptake rate limits to ensure high yields and volumetric productivity. When oxygen availability was limited, the specific oxygen uptake rate values were between 12 and 26 mg of O2/of g cell x h, resulting in a yield of 0.71 g of xylitol/xylose consumed, and 0.85 g/[L x h] for the volumetric productivity. According to the results, the effective control of the specific oxygen uptake rate makes it possible to establish complete control over this fermentative process, for both cell growth and xylitol production.

Modeling of the production of xylitol from d-xylose in a batch and continuous membrane bioreactor

This work presents a mathematical model that describes of the behavior of the main variable involved in the continuous bioconversion of xylose to xylitol by Candida guilliermondii in a stirred-tank bioreactor with total cell recycle, a promising process to obtain this polyol because it increases productivity in function of the high cellular density. The fermentation system was modeled considering cellular mass, xylose, xylitol and dissolved oxygen concentrations, as well as xylose reductase enzymatic activit as dependent variables. The model is based on the assumption of the intra/extracellular xylitol transport and it is able to represent inhibition by xylose on the main intracellular reaction (conversion of xylose to xylitol by xylose reductase) as well as the influence of the oxygen limitation in all steps of the bioconversion. The results of the mathamatical model simulation were compared to experimental data. The model represents quite well the yeast performance in the production of xylitol.