Positive Interactions between Lactic Acid Bacteria Promoted by Nitrogen-Based Nutritional Dependencies.

Area of Science:

• Microbiology
• Food Science
• Biotechnology

Background:

• Nutritional dependencies, particularly nitrogen sources, drive microbial interactions.
• Lactic acid bacteria (LAB) are crucial for fermented foods, but their positive interactions in artificial cocultures are underexplored.
• Previous studies focused on yogurt bacteria or antagonistic LAB interactions.

Purpose of the Study:

• To engineer positive interactions between LAB strains with different origins using nitrogen dependencies.
• To investigate how these engineered interactions impact functional outcomes like acidification, carbohydrate consumption, and volatile compound production.
• To leverage proteolytic activities and amino acid auxotrophies for coculture development.

Main Methods:

• Developed a chemically defined medium for six LAB strains (three proteolytic, three nonproteolytic).
• Created cocultures of proteolytic and nonproteolytic LAB strains.
• Monitored bacterial growth using compartmented chambers and evaluated acidification, carbohydrate consumption, and volatile compounds in direct cocultures.

Main Results:

• Proteolytic LAB strains induced varying interactions: strongly positive, weakly positive, or none.
• Strong interactions correlated with increased levels of specific amino acids (tryptophan, valine, phenylalanine, leucine, isoleucine) and peptides.
• Enhanced interactions led to faster acidification, lower pH, increased raffinose utilization, and higher production of five volatile compounds.

Conclusions:

• Proteolytic LAB strains differentially stimulate nonproteolytic LAB.
• The strength of LAB interactions directly influences functional outputs.
• This research provides a framework for creating novel LAB associations with guaranteed positive interactions for food applications.