CrossFeeding

Cross-feeding refers to metabolic interactions in which one organism releases compounds that are consumed by another, enabling growth and survival. It is common in microbial communities across soils, oceans, and the gut, and can stabilize diversity by linking metabolic pathways.

Mechanisms and metabolites: byproducts such as lactate, formate, acetate, succinate, ethanol, vitamins, and amino acids can serve as substrates. Interactions may be obligate (required for growth) or facultative. Spatial proximity and community structure influence the strength and outcome of cross-feeding.

Examples: In the anaerobic digestion ecosystem, fermentative bacteria produce hydrogen and acetate that methanogens consume, a process known as syntrophy. In the human gut, Bacteroides species release acetate and propionate used by other microbes, contributing to complex carbon flow. In aquatic systems, phototrophs excrete fixed carbon that heterotrophs utilize.

Significance and applications: Cross-feeding contributes to nutrient cycling, resilience, and community productivity. It is exploited in biotechnology to design synthetic microbial consortia for bioproduction and wastewater treatment. Researchers study cross-feeding using co-culture experiments, metagenomics, metabolomics, and stable isotope probing.

Challenges: Cross-feeding is highly context-dependent, varying with environmental conditions, resource supply, and community composition. Interactions can shift toward competition under stress. Understanding requires integrated ecological and metabolic models.