D- and L-lactate consumers are taxonomically, biochemically, and energetically different

Area of Science:

• Microbiology
• Metabolic Engineering
• Gut Microbiome Research

Background:

• D- and L-lactate are common microbial fermentation products.
• The microbial breakdown pathways for these lactate stereoisomers are not well understood.
• D-lactate is a digestion byproduct and a neurotoxin, making its microbial turnover relevant to host health.

Purpose of the Study:

• To investigate the microbial turnover of D- and L-lactate.
• To characterize microbial communities that consume lactate stereoisomers.
• To explore the ecological and clinical implications of lactate metabolism by gut microbes.

Main Methods:

• Enrichment of lactate-consuming microbial consortia using chemostat bioreactors.
• Cultivation in bioreactors with D- or L-lactate as the sole carbon source.
• Metagenomic and metaproteomic analyses to identify microbial players and metabolic pathways.

Main Results:

• Distinct microbial communities enriched on D-lactate (dominated by *Anaerotignum*) versus L-lactate (dominated by *Acidipropionibacterium* and *Propionibacterium*).
• Similar fermentation product spectra (acetate, propionate, CO2) regardless of lactate stereoisomer.
• Significantly lower biomass yield when feeding D-lactate compared to L-lactate, indicating different metabolic efficiencies.

Conclusions:

• Microbial metabolism of D- and L-lactate diverges significantly at phylogenetic and pathway levels, despite similar end products.
• Stereoisomer identity influences microbial niche specialization and ecological roles.
• Findings highlight the importance of lactate stereoisomerism in gut microbial ecology and its connection to host health.