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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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Gene expression of strain MG1363: differentially expressed genes (over- and under-expressed), in O2 condition in comparison to N2 condition grouped by COG categories (letters) at 1 h, 5 h, 8 h of culture in LM17 at 30°C. COG categories: Information storage and processing = > J “Translation, ribosomal structure and biogenesis”, K “Transcription”, L “DNA replication, recombination and repair”; Cellular processes = > D “Cell division and chromosome partitioning”, O “Posttranslational modification, protein turnover, chaperones”, M “Cell envelope biogenesis, outer membrane”, P “Inorganic ion transport and metabolism”, T “Signal transduction mechanisms”, U “Intracellular trafficking and secretion”; Metabolism = > C “Energy production and conversion”, G “Carbohydrate transport and metabolism”, E “Amino acid transport and metabolism”, F “Nucleotide transport and metabolism”, H “Coenzyme metabolism”, I “Lipid metabolism”, Q “Secondary metabolites biosynthesis, transport and catabolism”; Poorly characterized = > R “General function prediction only”, S “Function unknown”.
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Fig2: Gene expression of strain MG1363: differentially expressed genes (over- and under-expressed), in O2 condition in comparison to N2 condition grouped by COG categories (letters) at 1 h, 5 h, 8 h of culture in LM17 at 30°C. COG categories: Information storage and processing = > J “Translation, ribosomal structure and biogenesis”, K “Transcription”, L “DNA replication, recombination and repair”; Cellular processes = > D “Cell division and chromosome partitioning”, O “Posttranslational modification, protein turnover, chaperones”, M “Cell envelope biogenesis, outer membrane”, P “Inorganic ion transport and metabolism”, T “Signal transduction mechanisms”, U “Intracellular trafficking and secretion”; Metabolism = > C “Energy production and conversion”, G “Carbohydrate transport and metabolism”, E “Amino acid transport and metabolism”, F “Nucleotide transport and metabolism”, H “Coenzyme metabolism”, I “Lipid metabolism”, Q “Secondary metabolites biosynthesis, transport and catabolism”; Poorly characterized = > R “General function prediction only”, S “Function unknown”.

Mentions: Transcriptomic analysis was performed on the whole genome of strain MG1363. Differentially expressed (DE) genes in condition O2 in comparison to condition N2 were determined at different time points corresponding to stage A (1 h), stage B (5 h), stage C (8 h) and stage D (24 h). All DE genes are described in the supplementary data (Additional file1: Table S1) and DE genes discussed in the text are gathered in Table 1. Figure 2 represents the number of DE genes per known COG category, for each time point except 24 h (only one DE gene). The adaptation to oxygen strikingly occurred at 1 h (Figure 2.1) of culture (53 genes over-expressed and 37 genes under-expressed). All the COG categories were represented, indicating a global adaptation to oxidative stress. Moreover, COG categories C (energy production and conversion), E (amino acid transport and metabolism), F (nucleotide transport and metabolism) and O (post-transcriptional modification, protein turnover and chaperone) were specifically over-expressed in condition O2, clearly indicating that the cellular and energetic mechanisms were particularly affected at this early stage of growth. Only a small number of DE genes were observed at 5 h (Figure 2.2), most of which (11 out of 13) were under-expressed, probably because during stage B the absence of oxygen led to similar oxygen environment in both conditions O2 and N2, between 4 and 6 h of culture. In stage C (Figure 2.3), while dissolved oxygen increased again in the condition O2, only 23 genes were DE, of which 21 were under-expressed, indicating that the gene adaptation to oxygen observed in stage A did not occur despite the presence of oxygen.Table 1


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)

Gene expression of strain MG1363: differentially expressed genes (over- and under-expressed), in O2 condition in comparison to N2 condition grouped by COG categories (letters) at 1 h, 5 h, 8 h of culture in LM17 at 30°C. COG categories: Information storage and processing = > J “Translation, ribosomal structure and biogenesis”, K “Transcription”, L “DNA replication, recombination and repair”; Cellular processes = > D “Cell division and chromosome partitioning”, O “Posttranslational modification, protein turnover, chaperones”, M “Cell envelope biogenesis, outer membrane”, P “Inorganic ion transport and metabolism”, T “Signal transduction mechanisms”, U “Intracellular trafficking and secretion”; Metabolism = > C “Energy production and conversion”, G “Carbohydrate transport and metabolism”, E “Amino acid transport and metabolism”, F “Nucleotide transport and metabolism”, H “Coenzyme metabolism”, I “Lipid metabolism”, Q “Secondary metabolites biosynthesis, transport and catabolism”; Poorly characterized = > R “General function prediction only”, S “Function unknown”.
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Related In: Results  -  Collection

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Fig2: Gene expression of strain MG1363: differentially expressed genes (over- and under-expressed), in O2 condition in comparison to N2 condition grouped by COG categories (letters) at 1 h, 5 h, 8 h of culture in LM17 at 30°C. COG categories: Information storage and processing = > J “Translation, ribosomal structure and biogenesis”, K “Transcription”, L “DNA replication, recombination and repair”; Cellular processes = > D “Cell division and chromosome partitioning”, O “Posttranslational modification, protein turnover, chaperones”, M “Cell envelope biogenesis, outer membrane”, P “Inorganic ion transport and metabolism”, T “Signal transduction mechanisms”, U “Intracellular trafficking and secretion”; Metabolism = > C “Energy production and conversion”, G “Carbohydrate transport and metabolism”, E “Amino acid transport and metabolism”, F “Nucleotide transport and metabolism”, H “Coenzyme metabolism”, I “Lipid metabolism”, Q “Secondary metabolites biosynthesis, transport and catabolism”; Poorly characterized = > R “General function prediction only”, S “Function unknown”.
Mentions: Transcriptomic analysis was performed on the whole genome of strain MG1363. Differentially expressed (DE) genes in condition O2 in comparison to condition N2 were determined at different time points corresponding to stage A (1 h), stage B (5 h), stage C (8 h) and stage D (24 h). All DE genes are described in the supplementary data (Additional file1: Table S1) and DE genes discussed in the text are gathered in Table 1. Figure 2 represents the number of DE genes per known COG category, for each time point except 24 h (only one DE gene). The adaptation to oxygen strikingly occurred at 1 h (Figure 2.1) of culture (53 genes over-expressed and 37 genes under-expressed). All the COG categories were represented, indicating a global adaptation to oxidative stress. Moreover, COG categories C (energy production and conversion), E (amino acid transport and metabolism), F (nucleotide transport and metabolism) and O (post-transcriptional modification, protein turnover and chaperone) were specifically over-expressed in condition O2, clearly indicating that the cellular and energetic mechanisms were particularly affected at this early stage of growth. Only a small number of DE genes were observed at 5 h (Figure 2.2), most of which (11 out of 13) were under-expressed, probably because during stage B the absence of oxygen led to similar oxygen environment in both conditions O2 and N2, between 4 and 6 h of culture. In stage C (Figure 2.3), while dissolved oxygen increased again in the condition O2, only 23 genes were DE, of which 21 were under-expressed, indicating that the gene adaptation to oxygen observed in stage A did not occur despite the presence of oxygen.Table 1

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