Killer worms and germs: How within-host competition affects virulence

Infection of a host by more than one parasite genotype alters the selective environment faced by the parasite and may affect the virulent effects of the parasite on the host. The nature of these effects depends greatly on the mechanism of within-host competition. While exploitative competition is predicted to favor faster growing, more virulent parasites, interference competition is predicted to lead to the production of traits that may result in slower host exploitation. Here, I present work examining these two mechanisms of competition in natural community of entomopathogenic nematodes (Steinernema spp.) and their associated bacteria (Xenorhabuds spp.). We found that bacteria associated with these nematodes (Xenorhabdus spp.) produce bacteriocins, antimicrobial toxins, which were effective at killing other Xenorhabdus in the community. Moreover, we found that the production of these toxins increased the fitness of the producer if in competition with a sensitive competitor and that that bacteriocin activity within an insect host reduced the insect s probability of dying. Nevertheless, we also found that in the absence of bacteriocin activity, more virulent isolates were competitively dominant. Thus, our study supports the importance of understanding both exploitative and interference competition mechanisms for predicting the outcome of within-host selection.

Contact

  Megan A Greischar
  mag450@psu.edu