NIH4215: A mutation-prone thiamine auxotrophic clinical Aspergillus fumigatus isolate

• Published in: Frontiers in fungal biology Vol. 3; p. 908343
• Main Authors: Peres da Silva, Roberta, Brock, Matthias
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Media S.A 25.07.2022
• Subjects: akuB; bioluminescent reporter; DHN-melanin; Fungal Biology; nmt1; spontaneous mutations; thiamine biosynthesis; bioluminescent reporter; DHN-melanin; spontaneous mutations; akuB; Galleria mellonella; thiamine biosynthesis; nmt1
• ISSN: 2673-6128; 2673-6128
• DOI: 10.3389/ffunb.2022.908343

is the main cause of life-threatening invasive aspergillosis. Despite the availability of various antifungals, therapy remains challenging and requires further studies. Accordingly, the clinical isolate NIH4215 deriving from a fatal case of human pulmonary aspergillosis has frequently been used in drug efficacy studies. Unexpectedly, our initial attempts to generate a bioluminescent reporter of strain NIH4215 for drug efficacy studies failed, as NIH4215 was unable to grow on defined minimal medium. Subsequent analyses discovered a previously undescribed thiamine auxotrophy of strain NIH4215 and transformation with thiamine biosynthesis genes from strain Af293 identified the gene as cause of the thiamine auxotrophy. Sequencing of the defective gene revealed the loss of a cysteine codon within an essential iron-binding motif. Subsequently, the wild-type gene was successfully used to generate a bioluminescent reporter strain in NIH4215 by simultaneously deleting the locus. The resulting bioluminescent Δ strains showed a high frequency of homologous integration as confirmed by generation of and deletion mutants. When tested in a infection model, neither thiamine auxotrophy nor the deletion of the locus had a significant effect on virulence. However, besides thiamine auxotrophy, sectors with altered morphology and albino mutants frequently arose on colony edges of strain NIH4215 and its derivatives, and stable albino mutants were successfully isolated. A proposed increased mutation rate of NIH4215 was confirmed by screening for spontaneous occurrence of fluoorotic acid resistant mutants. Independent mutations in the and gene were identified in the fluoroorotic acid resistant NIH4215 isolates and the frequency of mutation was by at least one order of magnitude higher than that observed for the clinical isolate CBS144.89. In summary, despite its virulence in animal models, strain NIH4215 is a thiamine auxotroph and prone to accumulate mutations. Our results suggest that thiamine biosynthesis is dispensable for host infection and mutation-prone strains such as NIH4215 could potentially facilitate the evolution of azole resistant strains as increasingly observed in the environment.