The Wu lab is focused on understanding the mechanism of gum disease-associated dental biofilm formation and dispersal.
Fusobacterium nucleatum is an oral pathobiont not only associated with periodontitis, but also with extra-oral disease such as preterm birth and colorectal cancer. Our current study is focused on understanding the regulations that control F. nucleatum-mediated coaggregation. Coaggregation, defined as formation of aggregates caused by cell-to-cell recognition of genetically distinct bacteria via the interactions between adhesins and their cognate complementary receptors, is an important driving force for multispecies biofilm formation in nature. F. nucleatum is a prominent colonizer in dental plaque and has an outstanding coaggregation ability. F. nucleatum exhibits coaggregation with nearly all tested oral bacteria. Because of this, F. nucleatum has been proposed as a bridge microorganism in dental plaque by virtue of its coaggregation with early and late colonizers. In the past decades, intensive works have been done to find what bacteria can aggregate with F. nucleatum and what adhesins in F. nucleatum are responsible for their coaggregation. Studies of coaggregation have so far yielded four fusobacterial adhesins, RadD, CmpA, FomA and Fap2. Of these, FomA and Fap2 bind Porphyromonas gingivalis, CmpA binds a specific Streptococcus strain, and RadD, a versatile adhesin, mediates fusobacterial aggregation with many early and late colonizers, including Aggregatibacter actinomycetemcomitans. Vital for plaque development, this RadD-mediated coaggregation process is an excellent experimental model to study various cell-cell interactions within dental plaque. Theoretically, expression of adhesins in F. nucleatum should be tightly regulated since increasing surface adhesins promotes oral biofilm formation, and reducing their levels results in bacterial dispersal, which change the diversity and composition of dynamic dental plaque and probably shift a health-associated plaque to a pathogenic one. However, little known about the regulatory mechanisms underlying the multispecies interactions involving F. nucleatum. We use a multidisciplinary approach including genetic, biochemical methods, mass spectrometry, fluorescence confocal microscopy, electron microscopy to pursue the following questions related to RadD-mediated coaggregation
- How is RadD amount regulated?
We screened a fusobacterial transposon mutant library and identified a two-component system named coaggregation regulator CarS/CarR that regulates radD expression. We are interested in how CarSR influences radD level and then modules multispecies biofilm formation. We are also interested in the question what signal(s) are sensed by CarRS. RadD is a type V autotransporter. Fusobacterial surface displays several type V autotransporters, which are important virulence. We want to use RadD as a model to study the biogenesis of type V autotransporter in Gram-negative bacteria.
- How is RadD activity regulated?
Coaggregation not only tightly associates with RadD level, but also its activity. We discovered that free lysine in the environment modulates fusobacterial coaggregation “in situ” as lysine binds to RadD, thereby blocking RadD binding to its partners, and hence, co-aggregation. And we also found a nine-gene-operon that encodes a lysine-degrading pathway (LDP) controls environmental lysine level. LDP requires lysine catabolism to butyrate and ATP. A changing level of lysine present at gingival crevicular fluid (GCF), which provides nutrition for the microbial members within the subgingival plaque. We are interested in what is lysine source in GCF, how fusobacterial cells sense lysine and trigger LDP expression and what role of lysine and LDP in fusobacterium-mediated polymicrobial biofilm formation. Moreover, we are interested in whether host proteins also influence fusobacterium-mediated coaggregation and its pathogenesis.
- How coaggregation influences gene regulation in the partner organisms?
Cell-cell physical interactions alter metabolic and functional pathways in the partner organisms that may be essential for fusobacterial adaptation and survival in polymicrobial dental biofilm. These coaggregation-specific genes may be useful as biomarkers for dental plaque-associated oral disease. We are interested in what genes are coaggregation-depended and how those possible gene regulations occur in F. nucleatum.
Positions in the Wu Lab
The Wu lab has two NIH-funded postdoctoral positions available in the areas of oral bacteriology with gum disease focused on interactions between Fusobacterium nucleatum and oral microbiota/host. Candidate should have a Ph.D. degree in Bacteriology, Biochemistry or equivalent field. Experiments in RNA analysis, protein purification and bacterial genetics are needed. Interested candidates should send a detailed CV and the contact information of at least one referee to Dr. Chenggang Wu (Chenggang.email@example.com).