A search for contingency genes in Candida albicans : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand

Abstract

Many microbial pathogens have been known to use repeats in their cell wall pro- teins to generate diversity, and this has been found to contribute to their virulence. In bacteria, these genes are called contingency genes, and function to facilitate adap- tation of bacteria to the host environments as they invade di erent host parts and to evade the host's constantly evolving immune system. In the diploid Candida albicans, few genes have been classi ed as contingency genes due to the variation in the length of their repeat regions in di erent clinical isolates. This study attempts to answer a question of whether YWP1, HWP1, and EAP1 of C. albicans are contingency genes. These three genes encode cell wall proteins and contain repeats. For this purposes, allelic distributions of the genes in the general purpose genotype (GPG) and non-GPG strains (two groups with di erent genetic backgrounds), in commensal and infection strains, and in strains isolated from di erent sites of the humans body were examined. Based on the allelic distributions of the genes in GPG and non-GPG strains, it can be inferred that YWP1 and HWP1 can be categorized as contingency genes, while EAP1 cannot be categorized as a contingency gene. The allelic distributions of the genes in commensal and infection strains indicate that YWP1, HWP1, and EAP1 do not act as contingency genes when C. albicans state changes from commensal to pathogenic. Although the allelic distributions of the genes cannot distinguish com- mensal from infection strains, the non-random association between alleles of YWP1, HWP1, and EAP1 does distinguish these two groups, i.e. the YWP1 -HWP1 -EAP1 association is stronger in commensal strains that it is in infection strains. Based on the allelic distribution of the genes in strains isolated from di erent sites of the human body, it can be inferred that YWP1 and EAP1 do not act as contingency genes, but HWP1 may act as a contingency gene, when C. albicans moves to particular sites of the human body.