Navegando por Autor "Silveira, W. B."
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Item The activity of β-galactosidase and lactose metabolism in Kluyveromyces lactis cultured in cheese whey as a function of growth rate(Journal of Applied Microbiology, 2007-11-27) Ornelas, A. P.; Silveira, W. B.; Sampaio, F. C.; Passos, F. M. LKluyveromyces lactis was cultured in cheese whey permeate on both batch and continuous mode to investigate the effect of time course and growth rate on β-galactosidase activity, lactose consumption, ethanol production and protein profiles of the cells. Cheese whey was the substrate to grow K. lactis as a batch or continuous culture. In order to precise the specific growth rate for maximum β‐galactosidase activity a continuous culture was performed at five dilution (growth) rates ranging from 0·06, 0·09, 0·12, 0·18 to 0·24 h−1. The kinetics of lactose consumption and ethanol production were also evaluated. On both batch and continuous culture a respirofermentative metabolism was detected. The growth stage for maximum β‐gal activity was found to be at the transition between late exponential and entrance of stationary growth phase of batch cultures. Fractionating that transition stage in several growth rates at continuous culture a maximum β‐galactosidase activity at 0·24 h−1 was observed. Following that stage β‐gal activity undergoes a decline which does not correlate to the density of its corresponding protein band on the gel prepared from the same samples.The maximum β‐galactosidase activity per unit of cell mass was found to be 341·18 mmol ONP min−1 g−1 at a dilution rate of 0·24 h−1.The physiology of K. lactis growing in cheese whey permeate can proven useful to optimize the conversion of that substrate in biomass rich in β‐gal or in ethanol fuel. In addition to increasing the native enzyme the conditions established here can be set to increase yields of recombinant protein production based on the LAC4 promoter in K. lactis host.Item Ethanol production from cheese whey permeate by Kluyveromyces marxianus UFV-3: a flux analysis of oxido-reductive metabolism as a function of lactose concentration and oxygen levels(Enzyme and Microbial Technology, 2005-05-16) Silveira, W. B.; Passos, F. J. V.; Mantovani, H. C.; Passos, F. M. L.In order to investigate the effect of lactose concentration and oxygen level on the growth and metabolism of Kluyveromyces marxianus UFV-3 in cheese whey permeate, batch cultures were conducted under aerobic, hypoxic, and anoxic conditions, with lactose at initial concentration ranging from 1 to 240 g L^−1. The increase in lactose concentration increased ethanol yield and ethanol volumetric productivity, and has reduced cell yield. When lactose concentration was equal or above 50 g L^−1 and the oxygen levels were low, the ethanol yield was close to its theoretical value. Maximum ethanol concentrations attained in this study were 76 and 80 g L^−1 in hipoxia and anoxia, respectively. The lactose consumption rate in anoxia was greater than in aerobiosis and hipoxia. However, under anoxia, the lactose consumption rate of K. marxianus followed a saturation kinetics, which was not observed in hypoxia and aerobiosis. All oxygen levels investigated, showed a tendency for saturation of the ethanol production rate above 65 g L^−1 lactose. Ethanol production rate was also higher on anoxia.Item Kinetics and regulation of lactose transport and metabolism in Kluyveromyces lactis JA6(World Journal of Microbiology and Biotechnology, 2014-02-07) Santos, A. M.; Silveira, W. B.; Fietto, L. G.; Brandão, R. L.; Castro, I. M.Kluyveromyces lactis strains are able to assimilate lactose. They have been used industrially to eliminate this sugar from cheese whey and in other industrial products. In this study, we investigated specific features and the kinetic parameters of the lactose transport system in K. lactis JA6. In lactose grown cells, lactose was transported by a system transport with a half-saturation constant (K s) of 1.49 ± 0.38 mM and a maximum velocity (V max) of 0.96 ± 0.12 mmol. (g dry weight^)−1 h^−1 for lactose. The transport system was constitutive and energy-dependent. Results obtained by different approaches showed that the lactose transport system was regulated by glucose at the transcriptional level and by glucose and other sugars at a post-translational level. In K. lactis JA6, galactose metabolization was under glucose control. These findings indicated that the regulation of lactose-galactose regulon in K. lactis was similar to the regulation of galactose regulon in Saccharomyces cerevisiae.