Kylie J. Boyce, Yina Wang, Chengjun Cao, Surbhi Verma, Viplendra P. S. Shakya, Chaoyang Xue and Alexander Idnurm
The relative success of a species is determined by their ability to adapt rapidly to changes in environmental conditions. This adaptation occurs by the process of microevolution, in which a small proportion of the microbial population possessing phenotypes which facilitate growth are selected for and these cells become predominant in the population in a short time frame. Passaging of microbes in vitro can also lead to the selection of microevolved derivatives with differing properties to their original parent strains. The phenotypic traits are generated by mutations in the microbe’s DNA sequence arising from unrepaired errors occurring during DNA replication or from environmental damage to DNA. Mutations can be pre-existing in the microbe’s genome, or can be rapidly acquired in response to the host environment in a process termed adaptive evolution. Adaptive evolution is greatly enhanced by an increased mutation rate, which provides higher genetic diversity within a population on which selection can act. Strains which exhibit an elevated mutation rate, often 100-200-fold that of wildtype, are termed mutators. A mutator phenotype is advantageous in rapidly changing environmental or stressful conditions. The objective of this study was to ascertain if mutators existed within environmental, laboratory and clinical populations of Cryptococcus neoformans and to investigate the role mutation rate plays in microevolution and the emergence of resistance to antifungal drugs. The findings provide support for the hypothesis that this pathogenic fungus can take advantage of a mutator phenotype in order to cause disease, but only in specific pathways that lead to such a trait without a significant trade off in fitness.