title: Effect of culturing conditions on the expression of key enzymes in the proteolytic system of Lactobacillus bulgaricus.
abstract: The proteolytic system of Lactobacillus bulgaricus breaks down milk proteins into peptides and amino acids, which are essential for the growth of the bacteria. The aim of this study was to determine the expressions of seven key genes in the proteolytic system under different culturing conditions (different phases, initial pH values, temperatures, and nitrogen sources) using real-time polymerase chain reaction (RT-PCR). The transcriptions of the seven genes were reduced by 30-fold on average in the stationary phase compared with the exponential growth phase. The transcriptions of the seven genes were reduced by 62.5-, 15.0-, and 59.0-fold in the strains KLDS 08006, KLDS 08007, and KLDS 08012, respectively, indicating that the expressions of the seven genes were significantly different among strains. In addition, the expressions of the seven genes were repressed in the MRS medium containing casein peptone. The effect of peptone supply on PepX transcription was the weakest compared with the other six genes, and the impact on OppD transcription was the strongest. Moreover, the expressions of the seven genes were significantly different among different strains (P<0.05). All these results indicated that the culturing conditions affected the expression of the proteolytic system genes in Lactobacillus bulgaricus at the transcription level.
authors.affiliation: Key Laboratory of Dairy Science, Ministry of Education, Northeast Agricultural University, Harbin 150030, China; College of Food Science, Northeast Agricultural University, Harbin 150030, China; College of Animal Sciences, Zhejiang University, Hangzhou 310058, China.
authors.forename: Jun-cai
authors.initials: JC
authors.lastname: Hou
authors.forename: Fei
authors.initials: F
authors.lastname: Liu
authors.forename: Da-xi
authors.initials: DX
authors.lastname: Ren
authors.forename: Wei-wei
authors.initials: WW
authors.lastname: Han
authors.forename: Yue-ou
authors.initials: YO
authors.lastname: Du
mesh_terms: D019149:Bioreactors / Q000382:microbiology; D018929:Cell Culture Techniques / Q000379:methods*; D003470:Culture Media / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D007778:Lactobacillus / Q000166:cytology* / Q000201:enzymology*; D010447:Peptide Hydrolases / Q000096:biosynthesis* / Q000737:chemistry; D059748:Proteolysis
chemical_list: D003470:Culture Media; D010447:Peptide Hydrolases
keywords: Gene expression; Lactobacillus bulgaricus; Proteinase; Proteolytic system
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