Koaggregation

Koaggregation, often written coaggregation in English, is a phenomenon in microbiology in which cells of two or more different microbial species adhere to each other, forming mixed-species aggregates. This interspecies cell-to-cell adhesion plays a fundamental role in the organization of early biofilms and dental plaque. Coaggregation is driven by specific molecular interactions between surface structures on the participating organisms, such as adhesins, lectins, fimbriae, and receptors. The compatibility between species is often represented by coaggregation groups in dental microbiology, where certain Streptococcus and Actinomyces species exhibit mutually specific binding.

Experimentally, coaggregation is studied by mixing suspensions of two organisms and monitoring the rate or extent of aggregation, often by turbidity reduction, spectrophotometric assays, or microscopic observation. The strength and specificity of interactions can depend on environmental conditions like pH, ionic strength, temperature, and growth phase.

Ecologically, coaggregation contributes to the spatial organization of biofilms, enabling cross-feeding, signaling, and protection from environmental stress. In the oral cavity, coaggregation can influence the succession of early colonizers and the stability of the plaque ecosystem, with implications for dental caries and periodontal disease. Some species can act as bridges, enabling less compatible microbes to join the community.

Distinctions: coaggregation refers to interactions between cells of different species, whereas coadhesion typically describes attachment to a surface, and self-aggregation describes clumping within a single species.

See also: biofilms, microbial adhesion, dental plaque, receptor-ligand interactions.