title: The activity of beta-galactosidase and lactose metabolism in Kluyveromyces lactis cultured in cheese whey as a function of growth rate.
abstract: OBJECTIVE
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Departamento de Microbiologia, Instituto de Biotecnologia Aplicada à Agropecuária-BIOAGRO, Universidade Federal de Viçosa, Viçosa MG, Brazil.
authors.forename: A P
authors.initials: AP
authors.lastname: Ornelas
authors.forename: W B
authors.initials: WB
authors.lastname: Silveira
authors.forename: F C
authors.initials: FC
authors.lastname: Sampaio
authors.forename: F M L
authors.initials: FM
authors.lastname: Passos
mesh_terms: D019149:Bioreactors; D002611:Cheese; D004591:Electrophoresis, Polyacrylamide Gel; D000431:Ethanol / Q000378:metabolism; D005516:Food Microbiology; D007716:Kluyveromyces / Q000201:enzymology / Q000254:growth & development / Q000502:physiology*; D007785:Lactose / Q000032:analysis / Q000378:metabolism*; D008894:Milk Proteins / Q000378:metabolism; D009172:Mycology / Q000379:methods; D013995:Time; D001616:beta-Galactosidase / Q000032:analysis / Q000378:metabolism*
chemical_list: D008894:Milk Proteins; D000431:Ethanol; D001616:beta-Galactosidase; D007785:Lactose