Date of Award


Degree Type


Degree Name

Doctor of Philosophy in Biological and Environmental Sciences


Cell and Molecular Biology


Cell & Molecular Biology

First Advisor

Matthew M. Ramsey


Human supragingival plaque (SUPP) is a polymicrobial biofilm on the tooth surface above the gumline, comprised of ordered structures with spatial associations between specific bacterial taxa. Recent microscopy and microbiome data have suggested that some plaque structures are scaffolded by the abundant filamentous bacterium Corynebacterium matruchotii decorated with Streptococcus species. These taxa are able to make a reproducible structure known as the ‘Hedgehog’ model in vivo where Streptococcus species tend to form 'corncob' like structures around the terminal ends of C. matruchotii. As these species colocalize in vivo, we hypothesize that they also interact biochemically with one another. SUPP community composition has been well studied but not much is known about the mechanisms of bacterial-bacterial interactions between commensal organisms which allow these species to coexist in the plaque community.

In Chapter 2, we introduce new genetic tools that have been developed for the deliberate use in C. matruchotii. We describe the construction and use of a markerless clean deletion vector and promoter-reporter fusion vectors with mCherry and Renilla luciferase expression. Our last genetic tool is a conditional replicating mariner transposon vector created to increase transposition efficiency in C. matruchotii.

In Chapter 3, we investigate the biochemical interactions between C. matruchotii and the abundant oral streptococci, S. mitis. These SUPP commensals have been shown via microscopy data to interact in vivo and form corncob structures. S. mitis growth yield is increased in coculture with C. matruchotii aerobically while this growth benefit is lost anaerobically. C. matruchotii upregulates L-lactate catabolism genes when in coculture with S. mitis and a poor lactate catabolism strain of C. matruchotii (ΔlutABC) is less fit in coculture on limiting glucose. When oxygen is available, S. mitis produces H2O2 which C. matruchotii aids in detoxifying by its catalase function and protects itself by sequestering free iron with its ferritin.

In chapter 4, we investigate the interactions between C. matruchotii and abundant oral streptococci, S. cristatus, S. gordonii, and S. sanguinis through RNAseq analysis comparing mono- and coculture. All streptococci had a significant growth increase in coculture with C. matruchotii compared to monoculture. C. matruchotii increases expression of lactate catabolism genes and vitamin synthesis pathways when in coculture with S. cristatus and S. sanguinis. C. matruchotii also upregulates oxidative stress response genes, such as catalase and ferritin, when in coculture with S. sanguinis. When grown in saliva, C. matruchotii surprisingly upregulates many genes found upregulated with streptococci, but only fts genes were found to be downregulated in saliva media which may reveal why C. matruchotii is extremely filamentous in in vivo microscopy data. These findings further our understanding on the role of C. matruchotii within SUPP.



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