Sleepers and Creepers, Colony Polymorphisms in Metarhizium robertsii

Abstract

In this thesis I attempt to identify, describe, and explain the vast colony polymorphism differences observed in Metarhizium robertsii from a physical and genetic standpoint. These descriptions provide a framework to explain the colony polymorphisms seen in M. robertsii. This work is based on the observation of three distinct phenotypes: a highly conidiating phenotype (Sleeper), a primarily hyphal phenotype (Creeper) and an intermediary (Mixed) phenotype that represents the middle range between the Sleeper and Creeper phenotypes. Based on our findings, Sleepers typically have a higher fungal mass recovered from plant rhizospheres compared to Creepers and Mixed phenotypes. Creepers and Mixed strategy phenotypes are almost undifferentiable when grown on minimal nutrient medium whereas the Mixed and Sleepers tend to look very similar when grown on nutrient rich media. I concluded that the three phenotypes cannot be differentiated using artificial media. However, it was possible to differentiate between the Sleeper, Creeper and Mixed by infecting Great Wax Moth larvae (Galleria mellonella) with conidial suspension of M. robertsii. Key genes in the conidiation pathway, such as the methyltransferase MrDIM-2, may be relevant for differentiation between the Sleeper and Creeper/Mixed phenotypes. Expression levels of the Sleeper phenotype were found to be significantly lower than the Mixed or Creeper phenotypes.. The results have shown that MrDIM-2 expression influences either a Sleeper phenotype or a Mixed/Creeper phenotype presentation.