Candida parapsilosis is responsible for severe cases of non-albicans systemic candidiasis and is one of the leading causes of mortality in neonates. The molecular mechanisms underlying this organism's virulence remain unknown. Unlike C. albicans, which can exist in several morphogenetic forms, C. parapsilosis exists in either the yeast or pseudohyphal forms. The environmental signals that trigger pseudohyphal differentiation and the signalling pathways that transduce these signals are unknown. This paper provides evidence for the role of amino acids in morphogenesis in C. parapsilosis. The cell and colony morphologies, pseudohyphal differentiation and invasive growth of five C. parapsilosis isolates were characterized in ammonium-rich minimal media lacking or supplemented with naturally occurring amino acids. C. parapsilosis underwent dramatic changes in cellular and colony morphology and formed pseudohyphae in response to a specific subset of amino acids. Transport studies showed that these amino acid inducers activate the transport of some, but not all, unrelated amino acids. Interestingly, citrulline, an amino acid that is not transported in the presence of ammonium, strongly induced pseudohyphal morphogenesis in C. parapsilosis under these conditions. Together the data suggest that amino acids are important morphogens in C. parapsilosis and that amino-acid-mediated morphogenesis in this organism does not require transport of the ligand across the plasma membrane.
The entire operon encoding the sodium pumping cytochrome bo from the bacterium Vitreoscilla was isolated and sequenced, and this sequence was analyzed by blast and hydropathy plots. There are fairly similar phylogenetic relationships which apply to all five proteins, but overall greater similarity to members of the gamma subdivision than the beta subdivision of the Proteobacteria. Hydropathy plots of all five Cyo proteins show near identity with those of the corresponding E. coli subunits, indicating that the similarity extends from sequence to structure. The operon appears to have a typical Shine-Dalgarno sequence, an E. coli-like promoter, and several possible binding sites for regulatory proteins. The Vitreoscilla Cyo B subunit (the probable Na+ pump) is almost identical to E. coli Cyo B at 18 key amino acids; thus, there are no obvious changes in Vitreoscilla Cyo B that hint at the details of its Na+ pumping ability.
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