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Increased Filamentous Growth of Candida albicans in Simulated Microgravity.  L.E. Hyman, S. D. S.M. Altenburg. Y. Stypula, J. Ant and S. Nielsen-Preiss.   Division of Health Sciences and the Department of Cell Biology and Neuroscience, Montana State University, Bozeman MT 59717.

   Microgravity presents a unique environmental stress on prokaryotic and eukaryotic organisms that have evolved under normal gravity.  Determining the effects of this stress on cellular function during space flight is important to better understand the physiologic response of humans, and that of microorganisms that are potential human pathogens.  To this end, ground-based methods, such as the high-aspect-ratio-vessel (HARV) bioreactor, have been useful models to study a simulated microgravity (SMG) environment.  In previous studies from our laboratory, we examined the effects of SMG at both the phenotypic and genotypic level in Saccharomyces cerevisiae using the HARV bioreactor. Yeast grown under the influence of SMG displayed a random budding phenotype compared to the typical bipolar budding pattern of cells grown under control conditions.  In addition, we observed an increase in the number of cells found in clumps or aggregates.  Consistent with these phenotypic alterations, there were significant changes (≥1.5 fold) in the expression of genes associated with bipolar budding and cell separation.  In a separate but related study, genome wide microarray analysis revealed significant microgravity-induced changes in the expression of genes that have a role in environmental stress responses, as well as in genes that may represent novel responses to microgravity. 

    The objective of the current study was to determine the effects of SMG on C. albicans and establish whether the response is comparable to that observed in S. cerevisiae. Specifically, we examined whether a subset of genes conserved between S. cerevisiae and C. albicans respond in a similar fashion when grown under conditions of SMG.   In addition, we examined whether the phenotypic response to SMG observed in S. cerevisiae was mimicked by a morphogenic response in C. albicans, particularly to that which might induce a pathogenic response.  The results from this study provide evidence that there is a conserved response to SMG between two dissimilar yeast strains and the changes that occur in C. albicans may predict an increased pathogenicity.