title: Transcriptional responses in Lactococcus lactis subsp. cremoris to the changes in oxygen and redox potential during milk acidification.
abstract: Milk acidification and metabolic activity of the starter cultures are affected by oxygen; however, molecular factors related to the redox changes are poorly defined. The objective of the study was to investigate transcriptional responses in Lactococcus lactis subsp. cremoris CHCCO2 grown in milk to the shifts of oxygen and redox potential (Eh7 ). Transcriptomic studies were performed with the use of Illumina HiSeq 2000 mRNA sequencing and validated by the real-time quantitative PCR. In total 105 differentially expressed genes were assigned functional gene names. Most of the differentially expressed genes were detected during aerobic reduction phase. Upregulated genes were implicated in lactose utilization, glycogen biosynthesis, amino sugar metabolism, oxidation-reduction, pyrimidine biosynthesis and DNA integration processes. Genes of purine nucleotide biosynthesis and genes encoding amino acid, multidrug resistance and ion ABC transporters were mostly downregulated, while oligopeptide transporter genes were reduced during oxygen depletion and induced at minimum Eh7 .
  
  
  CONCLUSIONS
  Understanding of gene responses in starter cultures to the changes of oxidation-reduction state is important for the better control and reproducibility of dairy fermentations. We applied mRNA sequencing by Illumina HiSeq 2000 to investigate gene expression profile in a dairy strain of Lactococcus lactis subsp. cremoris during milk acidification. Novelty of this study lies in linking transcriptional responses to oxygen depletion and the changes of redox potential with the fermentation kinetics and clarification of molecular factors specifically expressed in milk which might be essential for bacterial performance and the final quality of cheeses.
authors.affiliation: Department of Food Science, Food Microbiology, University of Copenhagen, Frederiksberg C, Denmark.
authors.forename: N
authors.initials: N
authors.lastname: Larsen
authors.affiliation: Department of Food Science, Food Microbiology, University of Copenhagen, Frederiksberg C, Denmark.
authors.forename: B
authors.initials: B
authors.lastname: Brøsted Werner
authors.affiliation: Department of Food Science, Food Microbiology, University of Copenhagen, Frederiksberg C, Denmark.
authors.forename: L
authors.initials: L
authors.lastname: Jespersen
mesh_terms: D000818:Animals; D001483:Base Sequence; D002611:Cheese / Q000382:microbiology; D005285:Fermentation / Q000235:genetics*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D019344:Lactic Acid / Q000378:metabolism; D013294:Lactococcus lactis / Q000235:genetics* / Q000378:metabolism*; D007785:Lactose / Q000378:metabolism; D008892:Milk / Q000378:metabolism* / Q000382:microbiology; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D015203:Reproducibility of Results; D017423:Sequence Analysis, RNA; D059467:Transcriptome
chemical_list: D019344:Lactic Acid; D007785:Lactose; D010100:Oxygen
keywords: Lactococcus; acidification; gene expression; milk; redox potential