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Rerouting citrate metabolism in Lactococcus lactis to citrate-driven transamination
Agata M Pudlik1, Juke S Lolkema
1Top Institute Food and Nutrition, Wageningen, The Netherlands.
Applied and Environmental Microbiology
|July 17, 2012
Summary
Lactococcus lactis uses amino acid transamination to manage toxic oxaloacetate buildup, converting it into valuable cheese aroma compounds. This metabolic flexibility enhances cell survival and flavor production.
Area of Science:
- Microbiology
- Biochemistry
- Metabolic Engineering
Background:
- Oxaloacetate accumulates in Lactococcus lactis due to blocked citrate fermentation.
- High oxaloacetate levels create toxic stress within the cytoplasm.
- The citrate transporter CitP excretes excess oxaloacetate for external citrate.
Purpose of the Study:
- Investigate transamination as an alternative pathway for oxaloacetate detoxification.
- Determine if L. lactis transaminases can utilize oxaloacetate as a keto donor.
- Identify potential flavor compounds derived from citrate-driven transamination.
Main Methods:
- Culturing L. lactis with citrate and various amino acids (Ile, Leu, Val, Phe, Trp, Tyr, Met).
- Measuring cytoplasmic transaminase activity under different growth conditions.
- Analyzing metabolic products using biochemical assays and chromatography.
Main Results:
- Transamination of amino acids with oxaloacetate produced aspartate and corresponding α-keto acids.
- Cells grown with citrate exhibited 3.5-7 times higher transaminase activity.
- Methionine and phenylalanine transamination yielded precursors to cheese aroma compounds (2-hydroxy-4-methylthiobutyrate, methyl-3-methylthiopropionate, phenyllactate).
Conclusions:
- L. lactis transaminases effectively use oxaloacetate as a keto donor, alleviating toxic stress.
- Citrate metabolism can be redirected to amino acid transamination pathways.
- This metabolic route generates key cheese aroma compounds, linking cell physiology to flavor development.
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