Selection of Pneumocystis jirovecii Inosine 5'-Monophosphate Dehydrogenase Mutants in Solid Organ Transplant Recipients: Implication of Mycophenolic Acid

Mycophenolic acid (MPA) targets the inosine 5'-monophosphate dehydrogenase (IMPDH) of human lymphocytes. It is widely used as an immunosuppressant to prevent rejection in solid organ transplant (SOT) recipients who, incidentally, are at risk for Pneumocystis pneumonia (PCP). We hypothesized that MPA exerts selective pressure on P. jirovecii microorganisms considering its in vitro antifungal activity on other fungi. Thus, we analysed impdh gene in P. jirovecii isolates from SOT recipients. P. jirovecii specimens from 26 patients diagnosed with PCP from 2010 to 2020 were retrospectively examined: 10 SOT recipients treated with MPA and 16 non-SOT patients without prior exposure to MPA. The P. jirovecii impdh gene was amplified and sequenced. Nucleotide sequences were aligned with the reference sequences retrieved from available P. jirovecii whole genomes. The deduced IMPDH protein sequences were aligned with available IMPDH proteins from Pneumocystis spp. and other fungal species known to be in vitro sensitive or resistant to MPA. A total of nine SNPs was identified. One SNP (G1020A) that results in an Ala261Thr substitution was identified in all SOT recipients and in none of the non-SOT patients. Considering that IMPDHs of other fungi, resistant to MPA, harbour Thr (or Ser) at the analogous position, the Ala261Thr mutation observed in MPA-treated patients was considered to represent the signature of P. jirovecii exposure to MPA. These results suggest that MPA may be involved in the selection of specific P. jirovecii strains that circulate in the SOT recipient population.

[Yeasts from the CTG clade (Candida clade): Biology, impact in human health, and biotechnological applications]

Among the subdivision of Saccharomycotina (ascomycetes budding yeasts), the CTG clade (formerly the Candida clade) includes species that display a particular genetic code. In these yeasts, the CTG codon is predominantly translated as a serine instead of a leucine residue. It is now well-known that some CTG clade species have a major impact on human and its activities. Some of them are recognized as opportunistic agents of fungal infections termed candidiasis. In addition, another series of species belonging to the CTG clade draws the attention of some research groups because they exhibit a strong potential in various areas of biotechnology such as biological control, bioremediation, but also in the production of valuable biocompounds (biofuel, vitamins, sweeteners, industrial enzymes). Here we provide an overview of recent advances concerning the biology, clinical relevance, and currently tested biotechnological applications of species of the CTG clade. Future directions for scientific research on these particular yeasts are also discussed.

A synthetic construct for genetic engineering of the emerging pathogenic yeast Candida auris

Candida auris has recently emerged as a global cause of severe hospital-acquired fungal infections. To enable functional genomic approaches for this prominent pathogen, we designed a synthetic construct that can be used to genetically transform the genome-sequenced strain VPCI 479/P/13 of C. auris following an efficient electroporation procedure.