title: Characterization of lactose utilization and β-galactosidase in Lactobacillus brevis KB290, the hetero-fermentative lactic acid bacterium.
abstract: Unlike dairy lactic acid bacteria, Lactobacillus brevis cannot ferment milk. We characterized the lactose utilization by L. brevis KB290. In a carbohydrate fermentation assay using API 50 CHL, we showed during 7 days L. brevis did not ferment lactose. L. brevis grew to the stationary phase in 2 weeks in MRS broth containing lactose as the carbon source. L. brevis slowly consumed the lactose in the medium. L. brevis hydrolyzed lactose and a lactose analog, o-nitrophenyl-β-D-galactopyranoside (ONPGal). This β-galactosidase activity for ONPGal was not repressed by glucose, galactose, fructose, xylose, or maltose showing the microorganism may not have carbon catabolite repression. We purified the L. brevis β-galactosidase using ammonium sulfate precipitation and several chromatographies. The enzyme's molecular weight is estimated at 72 and 37 kDa using SDS-PAGE analysis. The N-terminal amino acid sequence of the larger protein was 90 % similar to the sequence of the putative β-galactosidase (YP_796339) and the smaller protein was identical to the sequence of the putative β-galactosidase (YP_796338) in L. brevis ATCC367. This suggests the enzyme is a heterodimeric β-galactosidase. The specific activity of the purified enzyme for lactose is 55 U/mg. We speculate inhibition of lactose transport delays the lactose utilization in L. brevis KB290.
authors.affiliation: Research Institute, Kagome Co., Ltd., 17 Nishitomiyama, Nasushiobara 329-2762, Japan. hiroyuki_honda@kagome.co.jp
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Honda
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Yajima
authors.forename: Tadao
authors.initials: T
authors.lastname: Saito
mesh_terms: D003470:Culture Media; D005285:Fermentation; D005947:Glucose / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism; D052196:Levilactobacillus brevis / Q000201:enzymology* / Q000254:growth & development / Q000378:metabolism; D007785:Lactose / Q000378:metabolism*; D009598:Nitrophenylgalactosides; D013379:Substrate Specificity; D001616:beta-Galactosidase / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D003470:Culture Media; C055012:2-nitrophenylgalactoside; D009598:Nitrophenylgalactosides; D019344:Lactic Acid; D001616:beta-Galactosidase; D005947:Glucose; D007785:Lactose