Development of cellulose-degrading lactic acid bacterium Lactococcus cremoris by genetic engineering.

Area of Science:

• Biotechnology
• Microbial Engineering
• Synthetic Biology

Background:

• Cellulose is an abundant, sustainable carbon source for biochemical production.
• Lactic acid bacteria (LAB), valuable metabolite producers, typically cannot metabolize cellulose.

Purpose of the Study:

• To engineer Lactococcus cremoris for growth on cellulosic substrates.
• To enable LAB to utilize cellulose for sustainable bioproduction.

Main Methods:

• Introduced heterologous cellulase genes (Cel5I, Cel9A, Cel5H) into L. cremoris.
• Evaluated constitutive expression using four promoters and two display methods (secretion/surface display).
• Assessed cellulolytic activity and growth on cellulose using various analytical techniques.

Main Results:

• Engineered L. cremoris secreted milligram quantities of active cellulases per liter.
• Secreted Cel5H and Cel5I showed high activity on amorphous and microcrystalline cellulose, respectively.
• Secreted cellulase strains demonstrated superior growth on phosphoric-acid swollen cellulose (PASC) compared to surface-displayed strains.

Conclusions:

• Demonstrated, for the first time, LAB growth on PASC as a primary carbon source using heterologous cellulases.
• This engineering advance is a key step towards consolidated bioprocesses utilizing LAB.
• Highlights the potential of engineered LAB for sustainable production of biochemicals from cellulosic biomass.