Genetic Characterization of phosphomannan biosynthesis in C. auris

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Candida auris is a recently emergent fungal pathogen. This newly emergent species has risen worldwide over the last ten years since its first recognition in Japan.This organism has become a public health problem due to its antifungal resistance and its ability to persist in critical care and nursing home facilities. One of the reasons behind this ability to persist is that many of the clinical isolates show multidrug resistance and, in rare cases, can be pan-resistant. Recently we examined the cell wall of eight C. auris isolates and discovered that C. auris mannans contain additional mannosyl phosphate (Mα1-PO4) branching that is unique to this species. This is a very exciting and potentially very important new finding. The fact that C. auris has an outer coating of mannan that is structurally distinct from all other Candida species and, indeed, any other fungal pathogen, suggests that the Mα1-PO4 structure distinguishes C. auris from other fungal pathogens. At this point, virtually nothing is known about the genes which control the expression of this unique cell wall phenotype. In C. albicans the Mnt3, Mnt5, and Mnn4 proteins are phosphmannosyltransferases responsible for phosphomannan biosynthesis. In addition there are seven Mnn4-like proteins that are functionally redundant with Mnn4 but do not play a major role in phosphomannan biosynthesis. A survey of the Candida Genome Database revealed that C. auris also contains the MNT3, MNT5, and MNN4 genes in addition to five MNN4-like genes. Due to the similarities of the genes in C. auris to those of C. albicans we hypothesize that the MNT3,MNT5 and MNN4 genes maintain a conserved role in phosphomannan biosynthesis, while one or more of the five MNN4-like genes have diverged to produce proteins that impact the Mα1-PO4 branching and/or phosphorylation. We will assess the role that these genes play via construction of deletion mutants in C. auris to determine if they impact phosphomannan biosynthesis and the addition of M1α-PO4 branching, using high field NMR. In addition we will determine if these mutants have increased or decreased attractiveness to human macrophages and their ability to kill the macropahges. From this work we expect to develop a better understanding of mannan biosynthesis in C. auris. The data generated will help to serve potential diagnostic and vaccine development in the future.