Characterization of the autoaggregation response of Fusobacterium nucleatum

Fusobacterium nucleatum is a Gram negative oral bacterial species associated with periodontal disease progression. This species is perhaps best known for its ability to adhere to a vast array of other bacteria and eukaryotic cells. Numerous studies of F. nucleatum have examined various coaggregation partners and inhibitors, but it is largely unknown whether these interactions induce a particular genetic response. We tested coaggregation between F. nucleatum ATCC strain 25586 and various species of Streptococcus in the presence of a semi-defined growth medium containing saliva. We found that this condition could support efficient coaggregation, but surprisingly also stimulated a similar degree of autoaggregation. We further characterized the autoaggregation response, since few reports have examined this in F. nucleatum. After screening several common coaggregation inhibitors, we identified L-lysine as a competitive inhibitor of autoaggregation. We performed a microarray analysis of the planktonic vs. autoaggregated cells and found nearly 100 genes that were affected after only about 60 min. of aggregation. We tested a subset of these genes via real-time RT-PCR and confirmed the validity of the microarray results. Some of these genes were also found to be inducible in cell pellets created by centrifugation. Based upon these data, it appears that autoaggregation activates a genetic program that may be utilized for growth in a high cell density environment, such as the oral biofilm. The study aims to determine the effect of autoaggregation upon the transcriptome. The study contains 2 separate experiments that both measure dispersed (i.e. non-aggregated) vs. aggregated cells and each experiment was performed in duplicate. Samples with no added components other than medium were dispersed, samples containing 25% saliva were aggregated, and samples containing 25% saliva + 50mM L-lysine remained dispersed.