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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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The pyruvate metabolism ofLactococcus lactis.ldh: gene coding for the lactate dehydrogenase; pdhA-D: genes coding for the pyruvate dehydrogenase complex; pfl: gene coding for pyruvate formate-lyase; adhE: gene coding for the acetaldehyde dehydrogenase; adhA: gene coding for the alcohol dehydrogenase; pta: gene coding for the phosphotransacetylase; ackA: gene coding for the acetate kinase, als: gene coding for catabolic and anabolic 2-acetolactate synthase; aldB-C: gene coding for the acetolactate decarboxylase; butA: gene coding for the diacetyl reductase; butB: gene coding for the acetoin reductase; noxE: gene coding for the NADH oxidase (NOX). Adapted from Oliveira et al.[29]. The blue area represents pathways up-regulated in O2 condition, and the yellow area represents pathways up-regulated in N2 condition.
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Fig3: The pyruvate metabolism ofLactococcus lactis.ldh: gene coding for the lactate dehydrogenase; pdhA-D: genes coding for the pyruvate dehydrogenase complex; pfl: gene coding for pyruvate formate-lyase; adhE: gene coding for the acetaldehyde dehydrogenase; adhA: gene coding for the alcohol dehydrogenase; pta: gene coding for the phosphotransacetylase; ackA: gene coding for the acetate kinase, als: gene coding for catabolic and anabolic 2-acetolactate synthase; aldB-C: gene coding for the acetolactate decarboxylase; butA: gene coding for the diacetyl reductase; butB: gene coding for the acetoin reductase; noxE: gene coding for the NADH oxidase (NOX). Adapted from Oliveira et al.[29]. The blue area represents pathways up-regulated in O2 condition, and the yellow area represents pathways up-regulated in N2 condition.

Mentions: As a type of homolactic bacteria, L. lactis produces mainly lactic acid from pyruvate, using glucose or lactose as carbon sources. However, other metabolites are simultaneously produced to a lesser extent from pyruvate using metabolic pathways dependent on culture conditions such as the oxygen level (Figure 3). Lactococcus lactis MG1363 displayed no differences in lactate dehydrogenase expression, under the two conditions O2 and N2. Besides this main pathway, the other pathways were affected under the condition O2. Genes pdhA-D, als and aldC, respectively encoding pyruvate dehydrogenase, acetolactate synthase, and alpha-acetolactate decarboxylase, were found to be over-expressed in condition O2 at 1 h (Table 1). Using RT-qPCR, genes pdhA and aldC were also found to be over-expressed at 5 h and 8 h (Table 2). It should be noted that the gene lplL, coding for a lipoate-protein ligase, which is adjacent to the pdh genes, also displayed an over-expression. On the contrary, under condition O2, genes adhE and fdhC (Table 1), respectively encoding alcohol acetaldehyde-dehydrogenase (AdhE) and formate dehydrogenase (FdhC), were under-expressed at 1 h. The gene pfl, encoding pyruvate formate lyase (PFL), responsible for the carbon flux from pyruvate to the formate/ethanol pathway (Figure 3), was over-expressed at 5 h (Table 1) indicating a switch from the aerobic to the anaerobic metabolism (Figure 3) during stage B. Finally, the gene frdC, coding for a flavoprotein involved in the reduction of fumarate to succinate, was under-expressed at 1 h.Figure 3


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)

The pyruvate metabolism ofLactococcus lactis.ldh: gene coding for the lactate dehydrogenase; pdhA-D: genes coding for the pyruvate dehydrogenase complex; pfl: gene coding for pyruvate formate-lyase; adhE: gene coding for the acetaldehyde dehydrogenase; adhA: gene coding for the alcohol dehydrogenase; pta: gene coding for the phosphotransacetylase; ackA: gene coding for the acetate kinase, als: gene coding for catabolic and anabolic 2-acetolactate synthase; aldB-C: gene coding for the acetolactate decarboxylase; butA: gene coding for the diacetyl reductase; butB: gene coding for the acetoin reductase; noxE: gene coding for the NADH oxidase (NOX). Adapted from Oliveira et al.[29]. The blue area represents pathways up-regulated in O2 condition, and the yellow area represents pathways up-regulated in N2 condition.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig3: The pyruvate metabolism ofLactococcus lactis.ldh: gene coding for the lactate dehydrogenase; pdhA-D: genes coding for the pyruvate dehydrogenase complex; pfl: gene coding for pyruvate formate-lyase; adhE: gene coding for the acetaldehyde dehydrogenase; adhA: gene coding for the alcohol dehydrogenase; pta: gene coding for the phosphotransacetylase; ackA: gene coding for the acetate kinase, als: gene coding for catabolic and anabolic 2-acetolactate synthase; aldB-C: gene coding for the acetolactate decarboxylase; butA: gene coding for the diacetyl reductase; butB: gene coding for the acetoin reductase; noxE: gene coding for the NADH oxidase (NOX). Adapted from Oliveira et al.[29]. The blue area represents pathways up-regulated in O2 condition, and the yellow area represents pathways up-regulated in N2 condition.
Mentions: As a type of homolactic bacteria, L. lactis produces mainly lactic acid from pyruvate, using glucose or lactose as carbon sources. However, other metabolites are simultaneously produced to a lesser extent from pyruvate using metabolic pathways dependent on culture conditions such as the oxygen level (Figure 3). Lactococcus lactis MG1363 displayed no differences in lactate dehydrogenase expression, under the two conditions O2 and N2. Besides this main pathway, the other pathways were affected under the condition O2. Genes pdhA-D, als and aldC, respectively encoding pyruvate dehydrogenase, acetolactate synthase, and alpha-acetolactate decarboxylase, were found to be over-expressed in condition O2 at 1 h (Table 1). Using RT-qPCR, genes pdhA and aldC were also found to be over-expressed at 5 h and 8 h (Table 2). It should be noted that the gene lplL, coding for a lipoate-protein ligase, which is adjacent to the pdh genes, also displayed an over-expression. On the contrary, under condition O2, genes adhE and fdhC (Table 1), respectively encoding alcohol acetaldehyde-dehydrogenase (AdhE) and formate dehydrogenase (FdhC), were under-expressed at 1 h. The gene pfl, encoding pyruvate formate lyase (PFL), responsible for the carbon flux from pyruvate to the formate/ethanol pathway (Figure 3), was over-expressed at 5 h (Table 1) indicating a switch from the aerobic to the anaerobic metabolism (Figure 3) during stage B. Finally, the gene frdC, coding for a flavoprotein involved in the reduction of fumarate to succinate, was under-expressed at 1 h.Figure 3

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