Phylogenetic relationships among members of the Fusarium solani species complex in human infections and the descriptions of F. keratoplasticum sp. nov. and F. petroliphilum stat. nov.

Fusarium species are frequently associated with mycotic keratitis and, to a lesser extent, cases of localized and disseminated infections. The Fusarium solani species complex (FSSC) is the most common group of fusaria associated with human infectious diseases. Several studies to date have revealed dozens of strongly supported phylogenetic species within this important evolutionary clade, though little work has been done to improve the taxonomy and understanding of the reproductive mode and phenotypes of the predominant clinically relevant species. Here we described Fusarium keratoplasticum sp. nov., and Fusarium petroliphilum stat. nov., two phylogenetic species that are among the most frequently isolated fusaria in plumbing drain biofilms and outbreaks of contact lens-associated mycotic keratitis. F. keratoplasticum isolates were highly variable and showed a range of morphological characteristics typical for most classical concepts of ‘F. solani.’ Many isolates failed to produce sporodochia and macroconidia. Although most attempts to sexually cross F. keratoplasticum isolates failed, a heterothallic sexual stage typical for the FSSC was discovered by pairing isolates of opposite mating type on V-8 agar, the ascospores of which showed molecular evidence of recombination. Secondary metabolite profiles of FSSC species defined through molecular data were compared for the first time and revealed the production of bioactive compounds including cyclosporines and several novel compounds of unknown function. We speculate that the inferred phenotypic variability in these species is the result of the almost entirely anthropogenic sources from which they are derived, including biofilms on plumbing systems.

► We describe two human pathogenic Fusarium species from plumbing drain biofilms.
► Four human pathogens within the Fusarium solani species complex were characterized.
► F. keratoplasticum Isolates were cross-fertile, producing recombinant ascospores.