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Ploidy and Allelic Variation Affects Fungal Pathogen Virulence in a Nematode Host

Feistel, Dorian Jay (2017)
Master's Thesis (31 pages)
Committee Chair / Thesis Advisers: Hickman, Meleah A; Morran, Levi T
Committee Members: Waller, Lance
Research Fields: Microbiology; Parasitology; Biology
Keywords: ploidy; allelic variation; virulence; Candida albicans; host-pathogen interaction
Program: Laney Graduate School, Biological and Biomedical Sciences (Population Biology, Ecology & Evolution)
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Genotype-by-genotype interactions between hosts and pathogens can play a significant role in determining pathogen virulence. In addition to allelic variation, ploidy is an important component of an individual genotype. Thus, the relative contributions of pathogen ploidy and allelic composition to pathogen virulence merit further investigation. Here, we investigated the effects of ploidy and allelic background on virulence in the fungal pathogen Candida albicans using the nematode Caenorhabditis elegans as a host. Using a near isogenic strain of C. elegans as the host permitted us to specifically characterize the pathogen side of this genotype-by-genotype interaction. We measured fecundity and survivability in C. elegans exposed to different C. albicans isolates that vary in their ploidy and allelic composition and found that both ploidy and allelic composition alter C. albicans virulence. We found that C. albicans negatively impacts both C. elegans survivability and fecundity. However, the degree to which C. elegans fitness was reduced varies, depending on the genetic background of C. albicans. The diploid laboratory reference strain SC5314 and its relative tetraploid displayed the highest degree of virulence on C. elegans fecundity, while the clinical FH tetraploid strain had decreased virulence relative to its diploid. This result suggests that ploidy and allelic contribution interact together to alter C. albicans virulence. Nematode survivability was significantly reduced when exposed to SC5314 diploids, but was not effected when exposed to its relative tetraploid. However, both SC5314 diploid and tetraploid delayed the reproductive timing in C. elegans, which consequently reduced the population growth. Taken together, our results suggest that the level of virulence expressed by C. albicans depends on a strain's ploidy and specific allelic combinations. Future studies that include a variety of host genotypes, such as immunocompromised or a heterozygous population of C. elegans, would increase the variance we observed in C. albicans virulence and potentially lead to a better understanding of genotype-by-genotype interactions between host and pathogen.

Table of Contents

Introduction 1

Methods 4

Strains and media 4

Seeding NGM plates for survival, fecundity,

and population growth assays 4

Egg preparation and synchronization for survival,

fecundity, and population growth assays 5

Survival assay 6

Fecundity assay 6

Population growth assay 6

Statistical analysis 7

Results 8

Exposure to C. albicans reduced C. elegans fitness 8

Genetic background affects C. albicans virulence 9

C. albicans ploidy and allelic background impacts virulence properties 10

C. albicans reduced population size of C. elegans 12

Discussion 13

Table 1 17

Figure 1 18

Figure 2 19

Figure 3 20

Figure 4 21

References 23


application/pdf Master's Thesis 31 pages (1.6 MB) [Access copy of Master's Thesis]
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