Influence of dual-species coaggregation on transcriptional changes of Streptococcus gordonii and Fusobacterium nucleatum subsp. polymorphum

Interspecies coaggregation promotes transcriptional changes of oral bacteria, contributing to the development of structurally balanced biofilms as well as oral diseases such as periodontitis. Streptococcus gordonii (S. gordonii) is an early colonizer of the oral cavity, and Fusobacterium nucleatum (F. nucleatum) may act as a bridge adhering to both early and late oral colonizers. These two species were commonly detected in healthy and periodontitis-diseased oral sites and could interact with immune cells such as macrophages. However, little research explored how intergeneric coaggregation affected transcriptional changes in S. gordonii and F. nucleatum subsp. polymorphum and how these gene changes might affect both species’ pathogenicity. The present study investigated transcriptional changes of both species in response to dual-species physical association using dual RNA-seq. Results indicated that after 30-min dual-species coaggregation, 148 genes were significantly up-regulated, and 124 genes were significantly down-regulated in S. gordonii. A total of 154 genes were significantly down-regulated, and 10 genes were significantly up-regulated in F. nucleatum subsp. polymorphum. A majority of up-regulated S. gordonii genes were involved in the biosynthesis and export of cell-wall proteins and the pathway of carbohydrate metabolism, and a group of down-regulated S. gordonii genes were associated with fatty acid biosynthesis and peptidoglycan biosynthesis. The transcriptome profiles indicated that the interspecies coaggregation led to a reduced level of DNA repair and lipopolysaccharides virulence in F. nucleatum subsp. polymorphum. The present study revealed that dual-species coaggregation induced a wide array of gene changes in S. gordonii and F. nucleatum subsp. polymorphum, enhancing S. gordonii’s adherence ability and attenuating F. nucleatum subsp. polymorphum's ability to produce LPS. Comparisons between transcriptional profiles of coaggregated S. gordonii (Group CAB) and mono-culture S. gordonii (Group Sg) were made to explore coaggregation-induced DEGs in S. gordonii DL1. Comparisons were also made between coaggregated F. nucleatum subsp. polymorphum (Group CAB) and mono-culture F. nucleatum subsp. polymorphum (Group Fnp) to investigate coaggregation-induced DEGs in F. nucleatum subsp. polymorphum. Note: Streptococcus gordonii DL1 and Streptococcus gordonii str. Challis substr. CH1 represent the same organism.