Chemotypic and genotypic diversity in the ergot alkaloid pathway of Aspergillus fumigatus

Aspergillus fumigatus is an opportunistic human pathogen that synthesizes a group of mycotoxins via a branch of the ergot alkaloid pathway. This fungus is globally distributed, and genetic data indicate that isolates recombine freely over that range; however, previous work on ergot alkaloids has focused on a limited number of isolates. We hypothesized that A. fumigatus harbors variation in the chemotype of ergot alkaloids and genotype of the ergot alkaloid gene cluster. Analysis of 13 isolates by high performance liquid chromatography revealed four distinct ergot alkaloid profiles or chemotypes. Five isolates completed the A. fumigatus branch of the ergot alkaloid pathway to fumigaclavine C. Six independent isolates accumulated fumigaclavine A, the pathway intermediate immediately before fumigaclavine C. One isolate accumulated only the early pathway intermediates chanoclavine-I and chanoclavine-I aldehyde, and one isolate lacked ergot alkaloids altogether. A genetic basis for each of the observed chemotypes was obtained either by PCR analysis of the ergot alkaloid gene cluster or through sequencing of easL, the gene encoding the prenyl transferase that reverse prenylates fumigaclavine A to fumigaclavine C. Isolates also exhibited differences in pigmentation and sporulation. The ergot alkaloid chemotypes were widely distributed geographically and among substrate of origin.