The Role of TssG, a Highly Conserved Component of the Type VI Secretion System, in Immune Modulation by Bordetella bronchiseptica

Open Access
Augustino, Melissa Gail
Area of Honors:
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Eric Thomas Harvill, Thesis Supervisor
  • Sarah Ellen Ades, Honors Advisor
  • Scott Brian Selleck, Faculty Reader
  • microbiology
  • bordetella
  • type VI secretion system
  • tssG
In recent years, a type VI secretion system (T6SS) has been discovered and characterized in many pathogens. However, many of the components of the secretion system have not been properly characterized. One of these subunits is the tssG gene (BB0800). Previous research has not determined a function or role for the highly conserved gene. We have studied the type VI secretion system in Bordetella bronchiseptica strain RB50, focusing specifically on tssG. We created recombinant TssG and introduced it to cultured macrophages. We then analyzed the media for cytotoxicity and the RNA present in the macrophages at varying time points to study the effect of TssG on the immune system. We determined cytotoxicity of TssG relative to RB50 based on the levels of LDH in the media following exposure to TssG. We concluded that TssG was not enough to cause cytotoxicity in cultured macrophages. We next analyzed RNA from the exposed cultured macrophages using RT-qPCR and compared the levels of IL-1β, IFN-γ, IL-4, IL-17, and IL-10. qPCR indicated that TssG downregulates the levels of IL-1β and IL-4 and upregulates the levels of IL-10. This change in cytokine production indicates that TssG acts on the immune system to limit inflammation as well as prevent the involvement of the adaptive immune response. Together, our data indicates that TssG is able to elicit an immune response from cultured macrophages and may play a role in the virulence of the type VI secretion system. However, further research and experiments must be conducted to confirm this role.