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Early adaptation to oxygen is key to the industrially important traits of Lactococcus lactis ssp. cremoris during milk fermentation.

Cretenet M, Le Gall G, Wegmann U, Even S, Shearman C, Stentz R, Jeanson S - BMC Genomics (2014)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK. sophie.jeanson@rennes.inra.fr.

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.

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Quantitative analysis by1H NMR of lactose and metabolites produced byLactococcus lactisMG1363 in LM17 under O2 condition (■) and under N2 condition () over 24 hours of culture at 30°C. Points are means of concentrations in mM (n = 3) and bars are standard deviations.
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Fig4: Quantitative analysis by1H NMR of lactose and metabolites produced byLactococcus lactisMG1363 in LM17 under O2 condition (■) and under N2 condition () over 24 hours of culture at 30°C. Points are means of concentrations in mM (n = 3) and bars are standard deviations.

Mentions: As a consequence of this early adaptation at the gene level, the metabolism was different under the two conditions 3 h into growth for most of the minor products derived from lactose. The metabolomics analysis performed using NMR analysis allowed to identify 27 metabolites (3 were only identified at the compound family level). Among them, 5 metabolites of major importance in the carbon metabolism of Lactococcus lactis had different kinetics of consumption or production under the two conditions. Figure 4 shows their kinetics (with the addition of lactose and lactate) at 7 time points over the 24 h-period. Lactose was not totally consumed at the end of the culture and its kinetics of consumption was not significantly different between the two conditions. Lactate was the main fermentation product in both conditions, with yields reaching 1.62 and 1.45 mol lactate per C6−mol of sugar consumed under conditions O2 and N2, respectively. On the contrary, minor products such as acetate, formate, ethanol and 2,3-butanediol displayed significantly different production kinetics under conditions O2 and N2 (Figure 4). While formate and ethanol were produced more under condition N2, acetate, 2,3-butanediol and acetoin were produced more under condition O2 (Figures 3 and4). The differences in these kinetics were observable, at the 3 or 5 h time point, and increased steadily over the whole 24 h-period, except for acetoin, which was increasingly transformed into 2,3-butanediol from 5 h onwards.Figure 4


Early adaptation to oxygen is key to the industrially important traits of Lactococcus lactis ssp. cremoris during milk fermentation.

Cretenet M, Le Gall G, Wegmann U, Even S, Shearman C, Stentz R, Jeanson S - BMC Genomics (2014)

Quantitative analysis by1H NMR of lactose and metabolites produced byLactococcus lactisMG1363 in LM17 under O2 condition (■) and under N2 condition () over 24 hours of culture at 30°C. Points are means of concentrations in mM (n = 3) and bars are standard deviations.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4289295&req=5

Fig4: Quantitative analysis by1H NMR of lactose and metabolites produced byLactococcus lactisMG1363 in LM17 under O2 condition (■) and under N2 condition () over 24 hours of culture at 30°C. Points are means of concentrations in mM (n = 3) and bars are standard deviations.
Mentions: As a consequence of this early adaptation at the gene level, the metabolism was different under the two conditions 3 h into growth for most of the minor products derived from lactose. The metabolomics analysis performed using NMR analysis allowed to identify 27 metabolites (3 were only identified at the compound family level). Among them, 5 metabolites of major importance in the carbon metabolism of Lactococcus lactis had different kinetics of consumption or production under the two conditions. Figure 4 shows their kinetics (with the addition of lactose and lactate) at 7 time points over the 24 h-period. Lactose was not totally consumed at the end of the culture and its kinetics of consumption was not significantly different between the two conditions. Lactate was the main fermentation product in both conditions, with yields reaching 1.62 and 1.45 mol lactate per C6−mol of sugar consumed under conditions O2 and N2, respectively. On the contrary, minor products such as acetate, formate, ethanol and 2,3-butanediol displayed significantly different production kinetics under conditions O2 and N2 (Figure 4). While formate and ethanol were produced more under condition N2, acetate, 2,3-butanediol and acetoin were produced more under condition O2 (Figures 3 and4). The differences in these kinetics were observable, at the 3 or 5 h time point, and increased steadily over the whole 24 h-period, except for acetoin, which was increasingly transformed into 2,3-butanediol from 5 h onwards.Figure 4

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK. sophie.jeanson@rennes.inra.fr.

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.

Show MeSH
Related in: MedlinePlus