Program Book - 27th Fungal Genetics Conference

CONCURRENT SESSION ABSTRACTSThursday, March 14 3:00 PM–6:00 PMKilnInteractions between Fungi and AnimalsCo-chairs: Neil Gow and Clarissa NobileElicitation of host damage occurs in a temporally programmed manner during Aspergillus fumigatus infections. Elaine M. Bignell. Microbiology Section,Imperial College London, London, United Kingdom.Background: In tissue-invasive lung infections caused by the mould Aspergillus fumigatus the molecular basis of host damage remains unclear. It has longbeen hypothesised that the secretion of proteolytic enzymes by invading A. fumigatus hyphae provides a mechanism by which epithelial damage ismediated. However, in whole animal studies of disease it has not been possible to substantiate an important role of fungal proteases since A. fumigatusmutants lacking individual or multiple enzyme functions retain the ability to cause fatal infections. One of the first cellular lines of defence against A.fumigatus infection is the monolayer of epithelial cells which line the mammalian airway. Epithelial cells provide a physical barrier against endothelialinvasion and initiate an inflammatory immune response upon contact with A. fumigatus spores. Here we show that the A. fumigatus pH-responsivetranscription factor, PacC, which governs expression of secreted proteases and secondary metabolism genes, is required for invasion of the murinepulmonary epithelium, and pathogenicity. Results: We determined, via murine and epithelial infection assays, that DpacC mutants are defective inelicitation of early-phase host damage which occurs, in wild type isolates, via a novel contact-dependent mechanism. Transcriptomic analyses of murineaspergillosis revealed aberrant cell wall biosynthesis in infecting DpacC isolates, suggesting a novel role for the A. fumigatus cell wall in pathogen-mediatedhost damage. Concordant with these findings PacC null mutants were shown to have signficiantly heightened chitin content in the fungal cell wall andwere hypersensitive to cell wall perturbing agents, including caspofungin. The mechanistic relevance of cell wall-mediated host damage was verified bycomparative analysis of damage elicited by cell wall extracts and heat-killed hyphae from wild type and DpacC isolates. Conclusion: A. fumigatus elicitshost damage in a biphasic manner, initally via a novel contact-dependent mechanism involving cell wall components, and later via soluble mediators. A.fumigatus mutants deficient in the pH-responsive transcription factor PacC suffer deficits in both mechanisms. On the basis of this functionaltranscriptomic analysis we propose a new model of biphasic host damage during A. fumigatus infections.Exploiting innate recognition of fungi for vaccine development. Stuart Levitz. Medicine, University of Massachusetts, Worcester, MA.Most licensed vaccines work by promoting protective antibody responses. However, some populations, such as the elderly and theimmunocompromised, generally have poor antibody responses to conventional vaccines. Moreover, for many infectious and neoplastic diseases, vaccinesthat arm adaptive T cell responses appear necessary. Thus, a major challenge in vaccinology is the development of platforms and adjuvants that effectivelypromote protective T cell and antibody responses. The immune system has evolved to innately recognize components of the fungal cell wall, particularly b-glucans. Research in my laboratory, in collaboration with Gary Ostroff, has focused on how this innate recognition of the fungal cell wall can be exploitedfor vaccine development. To achieve this aim, we have used glucan particles (GPs) as a novel vaccine platform. GPs are hollow, highly purifiedmicrocapsules prepared from Saccharomyces cerevisiae cell walls. GPs are composed predominantly of b-1,3-glucan and are recognized by b-glucanreceptors (particularly Dectin-1) on dendritic cells and other phagocytes. GPs also potently activate complement, resulting in opsonization and recognitionby complement receptors. GPs can be loaded with antigens and immunomodulators such that the “payload” is released following phagocytosis. We havedemonstrated robust and long-lasting antigen-specific T cell (Th1- and Th17-biased) and antibody responses following immunization of mice with GPs“encapsulated” with antibody. Moreover, vaccination of mice with GPs loaded with fungal antigens can protect mice against lethal challenges with thepathogenic fungi Cryptococcus neoformans and Histoplasma capsulatum.Regulatory circuits governing Candida albicans proliferation in a mammalian host. Jose C. Perez 1 , Carol A. Kumamoto 2 , Alexander D. Johnson 1 . 1)Microbiology and Immunology, UCSF, San Francisco, CA; 2) Molecular Biology and Microbiology, Tufts University, Boston, MA.The fungus Candida albicans resides in the gastrointestinal tract of most, if not all, human adults and is also a leading cause of life-threatening fungalinfections in immunocompromised individuals. C. albicans has no known environmental reservoir suggesting that it has extensively co-evolved to thrive inits host. To uncover the C. albicans gene circuits governing its proliferation in a host, we used mouse models of intestinal colonization and systemicinfection to screen a set of ~75 transcription regulator deletion strains. These mutant strains were chosen because they showed no gross phenotypeswhen cultured under a variety of laboratory growth conditions. We identified eight transcription regulators that play roles in intestinal colonization,systemic infection or both. Through genome-wide chromatin immunoprecipitation and transcriptional profiling experiments, we determined the targetgenes and the general circuitry controlled by these regulators. Our results reveal multiple biological functions necessary for C. albicans to inhabit amammalian host, the acquisition of carbon and nitrogen sources being prominent among them. These findings highlight common challenges faced bybacterial and eukaryotic (fungal) species when colonizing the mammalian intestine and illustrate how evolution has tinkered with the C. albicansregulatory circuitry to meet these demands.Dramatic ploidy change as an adaptive strategy in Candida albicans... Meleah A. Hickman, Ben Harrison, Darren Abbey, Anja Forche, Carsten Paulson,Kathleen Matter, Judith Berman. Dept Gen, Cell Biol & Dev, Univ Minnesota, Minneapolis, MN.For over 100 years, Candida albicans has been considered an obligate diploid, although it clearly tolerates single chromosome aneuploidy as well as longtracts of homozygosity. We recently identified tetraploid, triploid as well as intriguing reductions to below diploid C. albicans cells, some from the clinic,others from a mouse host and others following stress exposure in vitro. Tetraploidy arises either through parasex (mating between diploid cells) or defectsin mitosis. Stress conditions, including exposure to the antifungal drug flucanozole, increase the frequency of tetraploid formation. The polyploid state isrelatively unstable even under standard laboratory conditions and loss of a heterozygous marker increases by an order of magnitude as compared todiploid populations. A small subset of tetraploid cells return to a near diploid state very rapidly even without exposure to the stresses usually used toinduce concerted chromosome loss. The diploid derivatives of polyploid cells exhibit a wide range of chromosome aneuploidies and homozygosities, thusgenerating a wide range of genetic diversity within a single population. Evolution experiments with fluconazole suggest that diploid cells undergo transientpolyploidization in response to fluconazole and that polyploid cells adapt to stress conditions more rapidly.27th Fungal Genetics Conference | 55