Scientific Publications
Early adaptation to oxygen is key to the industrially important traits of Lactococcus lactis ssp. cremoris during milk fermentation
BMC Genomics, 15, December 2014
Background: Lactococcus lactis is the most used species in the dairy industry. It is thus important to understand its adaptation to technological stresses, such as oxidative stress encountered during stirring in the first steps of the cheese-making process. L. lactis is known to tolerate oxygen. This study aimed to understand the response to oxidative stress of Lactococcus lactis subsp. cremoris MG1363, 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 sharp decrease of the oxydo-reduction potential. The efficient consumption of oxygen by the L. lactis MG1363 strain was supported by a coherent and early adaptation at both gene expression and metabolic levels. For the first time, these results highlight an early and transitional adaptation to oxygen after 1 hour of culture. 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 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. As a consequence, key technological abilities such as acidification and redox potential decrease of the medium were conserved despite the presence of initially high levels of oxygen.
BMC Genomics, 15, December 2014
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