Role of Fusobacterium nucleatum and coaggregation in anaerobe survival in planktonic and biofilm oral microbial communities during aeration

Coaggregation is a well-characterized phenomenon by which specific pairs of oral bacteria interact physically. The aim of this study was to examine the patterns of coaggregation between obligately anaerobic and oxygen- tolerant species that coexist in a model oral microbial community. Obligate anaerobes other than Fusobacterium nucleatum coaggregated only poorly with oxygen-tolerant species. In contrast, F. nucleatum was able to coaggregate not only with both oxygen-tolerant and other obligately anaerobic species but also with otherwise-noncoaggregating obligate anaerobe-oxygen-tolerant species pairs. The effects of the presence or absence of F. nucleatum on anaerobe survival in both the biofilm and planktonic phases of a complex community of oral bacteria grown in an aerated (gas phase, 200 ml of 5% CO₂ in air· min^-1) chemostat system were then investigated. In the presence of F. nucleatum, anaerobes persisted in high numbers (>10⁷· ml^-1 in the planktonic phase and >10⁷ · cm^-2 in 4-day biofilms). In an equivalent culture in the absence of F. nucleatum, the numbers of black-pigmented anaerobes (Porphyromonas gingivalis and Prevotella nigrescens) were significantly reduced (P ≤ 0.001) in both the planktonic phase and in 4-day biofilms, while the numbers of facultatively anaerobic bacteria increased in these communities. Coaggregation-mediated interactions between F. nucleatum and other species facilitated the survival of obligate anaerobes in aerated environments.