Citrate Fermentation by Lactococcus and Leuconostoc spp

Area of Science:

• Microbiology
• Biochemistry
• Food Science

Background:

• Lactic acid bacteria (LAB) like Lactococcus lactis and Leuconostoc spp. are crucial in fermented foods.
• Understanding their metabolic regulation is key to optimizing fermentation processes.
• Pyruvate serves as a central intermediate in carbohydrate metabolism for these bacteria.

Purpose of the Study:

• To investigate the metabolic regulation of citrate and lactose fermentation in Lactococcus lactis and Leuconostoc spp.
• To elucidate the role of pyruvate as a key intermediate in these fermentation pathways.
• To determine the influence of environmental conditions (pH, aeration, substrate availability) on fermentation products.

Main Methods:

• Continuous and batch cultures of Lactococcus lactis subsp. lactis biovar diacetylactis and Leuconostoc spp. were employed.
• Metabolic pathways were analyzed under varying conditions of pH, lactose concentration, and aeration.
• Fermentation products and growth rates were quantified to assess metabolic activity and energy conservation.

Main Results:

• Lactococcus lactis exhibited flexible fermentation, producing lactate, ethanol, acetate, or acetoin/butanediol based on environmental cues.
• Leuconostoc spp. demonstrated limited flexibility, primarily producing d-lactate from pyruvate.
• Citrate utilization was optimal between pH 5.5-6.0 and significantly enhanced growth yields and energy conservation for both bacterial groups.

Conclusions:

• Metabolic regulation of citrate and lactose fermentation is linked, with pyruvate as the common intermediate.
• Environmental factors critically influence the fermentation pathways and end products in Lactococcus lactis.
• Citrate metabolism provides a significant energetic advantage, increasing growth yields in both Lactococcus lactis and Leuconostoc spp.