The effect of environmental variables in the human oral cavity on the balance between epiparasite TM7x and its host bacterium Actinomyces odontolyticus strain XH001.

TM7x is a recently cultivated bacterium of the phylum Candidatus Saccharibacteria (formerly TM7). TM7x is an ultrasmall bacterium and an obligate parasite that attaches to the surface of its bacterial host, Actinomyces odontolyticus strain XH001 (XH001). This episymbiotic pair are native to human subgingival plaque and display dynamic interaction during in vitro cultivation. Furthermore, an inverted relationship in abundance between Saccharibacteria and Actinomyces has been documented in healthy and periodontal conditions, implicating their association with periodontal status. In this thesis, I examine the impact of variable physiological factors associated with periodontitis, and other potential changes in the human oral cavity on the population dynamics of in vitro grown TM7x /XH001 episymbiont. Hydrogen peroxide as well as high concentration of sodium chloride and potassium chloride were found to reduce the amount of TM7x and result in increased relative abundance of TM7x-free XH001 in the XH001 / TM7x co-culture. In addition, fetal bovine serum increased the amount of TM7x attachment on XH001 cells to the point where XH001 growth was severely inhibited. Furthermore, XH001 monocultures are more resistant to alteration of their preferred microaerobic environment, while heat shock (at 42�C) did not shift the population balance between XH001 and TM7x. These data may lead us toward further understanding the environmental and host factors which modulate the balance between this parasite and its bacterial host