Selection of Streptococcus lactis Mutants Defective in Malolactic Fermentation

Area of Science:

• Microbiology
• Biochemistry

Background:

• Lactic acid bacteria play crucial roles in food fermentation and possess metabolic pathways like malolactic fermentation.
• Detecting variants in malolactic fermentation is essential for strain characterization and metabolic engineering.

Purpose of the Study:

• To develop and validate novel media for the detection of malolactic variants in lactic acid bacteria.
• To investigate the kinetics of malic acid conversion to lactic acid under various conditions.
• To characterize malolactic-negative mutants of Streptococcus lactis.

Main Methods:

• Development of an enrichment medium and a sensitive detection medium.
• Optimization of media components including glucose, l-malate concentration, pH, and indicator dyes.
• Induction of malolactic-negative mutants using UV, nitrosoguanidine, and transposonal mutagenesis.
• Characterization of mutant strains to identify genetic defects.

Main Results:

• The developed media enabled rapid and facile screening of malolactic variants.
• Kinetics of malic acid conversion were influenced by glucose and l-malate concentrations, pH, and indicator dye choice.
• Characterization revealed mutants with defects in the malolactic enzyme structural gene, a putative permease, or regulatory sequences.

Conclusions:

• The novel media are effective tools for identifying malolactic-negative mutants in lactic acid bacteria.
• Mutagenesis studies identified key genetic elements involved in malolactic fermentation in Streptococcus lactis.
• These findings contribute to a better understanding of malolactic pathway regulation and provide methods for strain improvement.