Characterization of Human Commensal Candida Albicans Hyphal Morphology

Abstract

A balanced and healthy microbiome is essential for the human host’s health. During periods of dysbiosis in a host, C. albicans acts as an opportunistic pathogen; when there is disruption to the environment that the fungus occupies C. albicans switches from a budding to a hyphal morphology. This morphological switch can lead to disseminated candidiasis which can further develop into infertility, pre-term birth, and other infectious diseases. The fungal cell wall plays a large role in pathogenicity and is essential to the survival and virulence of fungi such as Candida albicans. Hyphal growth and its causes have been studied, however specific cell wall features that contribute to this morphology have yet to be investigated thoroughly. In C. albicans hyphal growth can be induced by a range of factors, one of which has been identified to be peptidoglycan (PG) fragments from serum. This key finding suggests that interactions between bacteria and fungi contribute to an enhanced disease state during immune incompetence. Although it is known that the cAMP/PKA pathway is involved in PG induced hyphal formation, it remains unclear how these bacterial fragments enter the yeast cell and signal for hyphal growth. In this dissertation, I demonstrate how C. albicans uses both GlcNAc and MurNAc containing moieties from PG of bacterial cell walls to induce and sustain their pathogenic morphology. Initial growth screens of C. albicans and transcriptional analysis using qRT-PCR was carried out to identify if well-known hyphae specific genes (HSGs) are upregulated during PG induced hyphal morphogenesis. Further, we developed an enzymatic screening assay and a bio-orthogonal labeling method utilizing GlcNAc azide and alkyne probes to fluorescently label C. albicans via the chitin scavenging pathway. The methods developed here allow for continuous growth of chitin after incubation with the probes unlike current labeling methods. Moreover, high resolution fluorescent images of chitin in the filamentous hyphae morphology were obtained and indicate the probes utilization to study this pathogenic switch in more complex systems. Together, these results suggest that pathogenic fungi sense fragments from bacteria to induce and sustain the pathogenic hyphal morphology, indicating that inhibition of exogenous GlcNAc uptake for chitin biosynthesis serves as an excellent target for antifungals.