Mutation-Screening in l-(+)-Lactic Acid Producing Strains by Ion Implantation

Area of Science:

• Microbiology
• Biotechnology
• Industrial Fermentation

Background:

• Lactic acid is a valuable chemical with diverse industrial applications.
• Improving lactic acid yield from microbial fermentation is crucial for economic viability.
• Lactobacillus casei is a known producer of lactic acid, but strain optimization is needed.

Purpose of the Study:

• To enhance the yield of l-(+)-lactic acid from Lactobacillus casei.
• To identify optimal conditions for nitrogen ion implantation mutagenesis.
• To develop a more efficient screening method for high-yield mutants.

Main Methods:

• Mutagenesis of wild-type Lactobacillus casei CICC6028 using nitrogen ion implantation.
• Optimization of nitrogen ion implantation parameters (output power and dose).
• Development and application of a novel screening method to identify high-yield mutants, replacing the transparent halos method.

Main Results:

• Optimal mutation conditions were identified as 10 keV output power and a dose of 50 × 2.6 × 10^13 ions/cm^2.
• A superior mutant strain, designated N-2, was isolated.
• Mutant N-2 exhibited an increased optimal fermentation temperature (40°C) and achieved an l-(+)-lactic acid yield of 136 g/l, compared to 98 g/l for the wild-type strain at 34°C.

Conclusions:

• Nitrogen ion implantation is an effective method for generating high-yield lactic acid producing strains of Lactobacillus casei.
• The developed screening strategy successfully identified a significantly improved mutant.
• The mutant strain N-2 demonstrates considerable potential for industrial-scale l-(+)-lactic acid production.