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Open Access Publications from the University of California

Scholarly Works (2 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2013)

Periodontal disease is a highly common disorder believed to be triggered by colonization of bacteria on the surface of teeth. Although the relationship between many oral bacterial species has been shown to rely on physical adherence, the intracellular consequences that arise as a result of these intimate associations are currently unknown. Fusobacterium nucleatum (F.n), a Gram-negative periodontal pathogen that has the unique capability to adhere to Gram-positive primary colonizing and Gram-negative secondary colonizing oral bacteria was chosen to assess differential gene regulation that may occur in response to a primary colonizer, Streptococcus sanguinis (S.s.). A mutant strain of F.n that lacks RadD, an outer-membrane adhesin required for adherence and recognition of Gram-positive oral streptococci, was also used to determine if RadD-dependent gene regulation in response to S.s was present. RNA was extracted from wildtype F.n. and the ΔRadD mutant alone, as well as after co-incubation with S.s., and the expression profile of twenty-four F.n. genes selected from a previous microarray study for validation was determined via Real-Time Polymerase Chain Analysis (RT-PCR). We found that of the twenty-four genes tested, seventeen showed differential regulation in wildtype F.n. in the presence of S.s., twenty were regulated in the ΔRadD mutant in response to S.s., while five exhibited transcriptional differences due to lack of RadD independent of S.s. when the expression profile of the ΔRadD mutant was compared to wildtype. Compared to wildtype F.n., six genes showed opposite regulation in the ΔRadD mutant in response S.s., indicating that there is contact-dependent gene regulation mediated by the RadD adhesin. Aside from providing an intracellular understanding of contact-dependent adherence between two prominent oral bacteria, to the best of our knowledge, this is the first discovery of expression of genes that rely on the presence of an interspecies recognition based outer membrane adhesin in a bacterial species.

    Cover page: Determination of RadD-Dependent Gene Regulation in Fusobacterium nucleatum in Response to Streptococcus sanguinis
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2014)
    The classic organization by Socransky and coworkers categorized the oral bacteria of the subgingival plaque into different complexes. Treponema denticola, Porphyromonas gingivalis and Tannerella forsythia are grouped into the red complex that is highly correlated with periodontal disease. Socransky's work closely associates red with orange complex species such as Fusobacterium nucleatum and Prevotella intermedia but not with members of the other complexes. While the relationship between species contained by these complexes is in part supported by their ability to physically attach to each other, the physiological consequences of these interactions and associations are less clear. In this study, we employed T. denticola as a model organism to analyze contact-dependent responses to interactions with species belonging to the same complex (P. gingivalis and T. forsythia), the closely associated orange complex (using F. nucleatum and P. intermedia as representatives) and the unconnected yellow complex (using Streptococcus sanguinis and S. gordonii as representatives). RNA was extracted from T. denticola alone as well as after pairwise co-incubation for 5 hrs with representatives of the different complexes, and the respective gene expression profiles were determined using microarrays. Numerous genes related to motility, metabolism, transport, outer membrane and hypothetical proteins were differentially regulated in T. denticola in the presence of the tested partner species. Further analysis revealed a significant overlap in the affected genes and we identified a general response to the presence of other species, those specific to two of the three complexes as well as individual complexes. Most interestingly, many predicted major antigens (e.g. flagella, Msp, CTLP) were suppressed in responses that included red complex species indicating that the presence of the most closely associated species induces immune-evasive strategies. In summary, the data presented here provide an in-depth understanding of the transcriptional responses triggered by contact-dependent interactions between microorganisms inhabiting the periodontal pocket.
      Cover page: Transcriptional Responses of Treponema denticola to Other Oral Bacterial Species
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