title: Early adaptation to oxygen is key to the industrially important traits of Lactococcus lactis ssp. cremoris during milk fermentation.
abstract: BACKGROUND
  Lactococcus lactis is the most used species in the dairy industry. Its ability to adapt to technological stresses, such as oxidative stress encountered during stirring in the first stages of the cheese-making process, is a key factor to measure its technological performance. This study aimed to understand the response to oxidative stress of Lactococcus lactis subsp. cremoris MG1363 at the transcriptional and metabolic levels in relation to acidification kinetics and growth conditions, especially at an early stage of growth. For those purposes, conditions of hyper-oxygenation were initially fixed for the fermentation.
  
  
  RESULTS
  Kinetics of growth and acidification were not affected by the presence of oxygen, indicating a high resistance to oxygen of the L. lactis MG1363 strain. Its resistance was explained by an efficient consumption of oxygen within the first 4 hours of culture, leading to a drop of the redox potential. The efficient consumption of oxygen by the L. lactis MG1363 strain was supported by a coherent and early adaptation to oxygen after 1 hour of culture at both gene expression and metabolic levels. In oxygen metabolism, the over-expression of all the genes of the nrd (ribonucleotide reductases) operon or fhu (ferrichrome ABC transports) genes was particularly significant. In carbon metabolism, the presence of oxygen led to an early shift at the gene level in the pyruvate pathway towards the acetate/2,3-butanediol pathway confirmed by the kinetics of metabolite production. Finally, the MG1363 strain was no longer able to consume oxygen in the stationary growth phase, leading to a drastic loss of culturability as a consequence of cumulative stresses and the absence of gene adaptation at this stage.
  
  
  CONCLUSIONS
  Combining metabolic and transcriptomic profiling, together with oxygen consumption kinetics, yielded new insights into the whole genome adaptation of L. lactis to initial oxidative stress. An early and transitional adaptation to oxidative stress was revealed for L. lactis subsp. cremoris MG1363 in the presence of initially high levels of oxygen. This enables the cells to maintain key traits that are of great importance for industry, such as rapid acidification and reduction of the redox potential of the growth media.
authors.forename: Marina
authors.initials: M
authors.lastname: Cretenet
authors.forename: Gwenaëlle
authors.initials: G
authors.lastname: Le Gall
authors.forename: Udo
authors.initials: U
authors.lastname: Wegmann
authors.forename: Sergine
authors.initials: S
authors.lastname: Even
authors.forename: Claire
authors.initials: C
authors.lastname: Shearman
authors.forename: Régis
authors.initials: R
authors.lastname: Stentz
authors.affiliation: Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK. sophie.jeanson@rennes.inra.fr.
authors.forename: Sophie
authors.initials: S
authors.lastname: Jeanson
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics*; D000818:Animals; D002417:Cattle; D005285:Fermentation / Q000235:genetics; D005516:Food Microbiology; D013294:Lactococcus lactis / Q000235:genetics* / Q000254:growth & development; D055432:Metabolomics; D008892:Milk / Q000378:metabolism / Q000382:microbiology; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000235:genetics*; D010100:Oxygen / Q000378:metabolism; D010641:Phenotype; D059467:Transcriptome / Q000235:genetics*
chemical_list: D010100:Oxygen