|Fog Nielsen, Kristian|
Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2013
Publication Date: 4/1/2013
Citation: Short, D.P., O'Donnell, K., Thrane, U., Fog Nielsen, K., Zhang, N., Juba, J.H., Geiser, D.M. 2013. 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. Fungal Genetics and Biology. 53(2013):59-70. Interpretive Summary: The number of superficial and deeply invasive, life-threatening infections caused by species of the filamentous fungus Fusarium have increased dramatically over the past 20 years, especially within the rapidly growing population of immunosuppressed and immunocompromised patients. Roughly two-thirds of fusarial infections are caused by members of one genetic group referred to as the F. solani species complex (FSSC). Of the approximately 20 FSSC species that have been implicated in infections of humans and other animals, two unnamed species informally designated FSSC 1 and FSSC 2 account for a disproportionate number of infections. Here, we analyzed isolates of both species to identify distinctive morphological features, and to assess their ability to complete a sexual cycle in the laboratory and to produce bioactive compounds. Based on the results of these analyses, FSSC 1 and FSSC 2 were formally described as F. petroliphilum and F. keratoplasticum, respectively. Results of this study should benefit and be of interest to clinical microbiologists and infectious disease specialists who are charged with diagnosing and treating fungal infections. Furthermore, knowledge that both species are very common in plumbing drain biofilms will benefit epidemiologists who will be informed to reduce the exposure of immunologically impaired or suppressed patients to a major source of these opportunistic pathogens.
Technical Abstract: 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.