Harnessing Adaptive Evolution to Achieve Superior Mannitol Production by Lactococcus lactis Using Its Native...

Area of Science:

• Microbiology
• Biotechnology
• Metabolic Engineering

Background:

• Mannitol is a sugar alcohol typically produced by heterolactic bacteria from fructose.
• Lactococcus lactis, a homolactic bacterium, usually does not produce mannitol but can be modified to do so.

Purpose of the Study:

• To investigate the inherent capacity of Lactococcus lactis to produce mannitol from glucose.
• To enhance mannitol production in L. lactis through adaptive evolution and metabolic pathway manipulation.

Main Methods:

• Adaptive evolution of L. lactis strains, particularly those with blocked NAD+ regenerating pathways.
• Culturing adapted strains in glucose-containing media to assess mannitol conversion rates.
• Inactivation of the mannitol uptake system to further improve yields.
• Two-stage culturing (aerated followed by static conditions) for biomass accumulation and mannitol production.

Main Results:

• Adapted L. lactis strains converted 4-58% of metabolized glucose into mannitol, significantly higher than non-adapted strains.
• A strain lacking major NAD+ regenerating pathways showed the highest conversion efficiency.
• Inactivating the mannitol uptake system increased glucose conversion to 60%.
• A two-stage cultivation yielded 6.1 g/L of mannitol, representing the highest reported yield for L. lactis.

Conclusions:

• Lactococcus lactis possesses an intrinsic ability to convert glucose to mannitol, which can be significantly enhanced through adaptive evolution.
• Metabolic engineering strategies, including pathway blocking and uptake system inactivation, are effective in maximizing mannitol production.
• Optimized fermentation conditions in L. lactis offer a promising route for efficient mannitol biosynthesis.