Microbiologia

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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. L
Kluyveromyces 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.
Computational analysis of the interaction between transcription factors and the predicted secreted proteome of the yeast Kluyveromyces lactis
(BMC Bioinformatics, 2009-06-25) Brustolini, Otávio JB; Fietto, Luciano G; Cruz, Cosme D; Passos, Flávia ML
Protein secretion is a cell translocation process of major biological and technological significance. The secretion and downstream processing of proteins by recombinant cells is of great commercial interest. The yeast Kluyveromyces lactis is considered a promising host for heterologous protein production. Because yeasts naturally do not secrete as many proteins as filamentous fungi, they can produce secreted recombinant proteins with few contaminants in the medium. An ideal system to address the secretion of a desired protein could be exploited among the native proteins in certain physiological conditions. By applying algorithms to the completed K. lactis genome sequence, such a system could be selected. To this end, we predicted protein subcellular locations and correlated the resulting extracellular secretome with the transcription factors that modulate the cellular response to a particular environmental stimulus. To explore the potential Kluyveromyces lactis extracellular secretome, four computational prediction algorithms were applied to 5076 predicted K. lactis proteins from the genome database. SignalP v3 identified 418 proteins with N-terminal signal peptides. From these 418 proteins, the Phobius algorithm predicted that 176 proteins have no transmembrane domains, and the big-PI Predictor identified 150 proteins as having no glycosylphosphatidylinositol (GPI) modification sites. WoLF PSORT predicted that the K. lactis secretome consists of 109 putative proteins, excluding subcellular targeting. The transcription regulators of the putative extracellular proteins were investigated by searching for DNA binding sites in their putative promoters. The conditions to favor expression were obtained by searching Gene Ontology terms and using graph theory. A public database of K. lactis secreted proteins and their transcription factors are presented. It consists of 109 ORFs and 23 transcription factors. A graph created from this database shows 134 nodes and 884 edges, suggesting a vast number of relationships to be validated experimentally. Most of the transcription factors are related to responses to stress such as drug, acid and heat resistance, as well as nitrogen limitation, and may be useful for inducing maximal expression of potential extracellular proteins.
The activity of b-galactosidase and lactose metabolism in Kluyveromyces lactis cultured in cheese whey as a function of growth rate
(Journal of Applied Microbiology, 2007-09-13) Ornelas, A.P.; Silveira, W.B.; Sampaio, F.C.; Passos, F.M.L.
Kluyveromyces lactis was cultured in cheese whey permeate on both batch and continuous mode to investigate the effect of time course and growth rate on beta-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 beta-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 beta-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 beta-galactosidase activity at 0.24 h(-1) was observed. Following that stage beta-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 beta-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 beta-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.

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