Skip to main content
ARS Home » Midwest Area » Peoria, Illinois » National Center for Agricultural Utilization Research » Mycotoxin Prevention and Applied Microbiology Research » Research » Publications at this Location » Publication #302647
Title: Clonality, recombination, and hybridization in the plumbing-inhabiting human pathogen Fusarium keratoplasticum inferred from multilocus sequence typing

Author
item SHORT, DYLAN P. - University Of California
item O Donnell, Kerry
item GEISER, DAVID - Pennsylvania State University

Submitted to: BMC Evolutionary Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2014
Publication Date: 4/26/2014
Citation: Short, D.G., O'Donnell, K., Geiser, D.M. 2014. Clonality, recombination, and hybridization in the plumbing-inhabiting human pathogen Fusarium keratoplasticum inferred from multilocus sequence typing. BMC Evolutionary Biology. 14:91

Interpretive Summary: Prior research has shown that many of the molds in the genus Fusarium that are associated with infections of humans and other animals appear to be common in plumbing systems. The present study was conducted to better understand the genetic diversity and population biology of the Fusarium species most commonly isolated from plumbing biofilms, F. keratoplasticum. This cosmopolitan fungus is known almost exclusively from animal infections and biofilms. We sequenced and analyzed DNA sequence data from portions of nine genes to make inferences about its population biology. High levels of genetic diversity and evidence for sexual recombination and clonality were detected among 75 clinical and 156 environmental isolates of F. keratoplasticum. The multilocus sequence typing system resolved 111 unique sequence types (STs). All but one of the 49 isolates of the most common ST (FSSC 2d-2) came from human infections, mostly of the cornea, and from biofilms associated with contact lenses and plumbing surfaces. Discordance between the gene genealogies is consistent hybridization between F. keratoplasticum and another Fusarium species designated FSSC 9. No significant population subdivision based on clinical versus non-clinical sources was found. Overall, F. keratoplasticum is a diverse and geographically unstructured species with a mixed clonal and recombinant life history.

Technical Abstract: Recent work has shown that Fusarium species and genotypes most commonly associated with human infections, particularly of the cornea (mycotic keratitis), are the same as those most commonly isolated from plumbing systems. The species most dominant in plumbing biofilms is Fusarium keratoplasticum, a cosmopolitan fungus known almost exclusively from animal infections and biofilms. To better understand its diversity and population dynamics, we developed and utilized a nine-locus sequence-based typing system to make inferences about clonality, recombination, population structure, species boundaries, and hybridization. High levels of genetic diversity and evidence for recombination and clonality were detected among 75 clinical and 156 environmental isolates of Fusarium keratoplasticum. The multilocus sequence typing system (MLST) resolved 111 unique nine-locus sequence types (STs). The single locus bifactorial determinants of mating compatibility (mating types MAT1-1 and MAT1-2), were found in a ratio of 70:30. All but one of the 49 isolates of the most common ST (FSSC 2d-2) came from human infections, mostly of the cornea, and from biofilms associated with contact lenses and plumbing surfaces. Significant levels of phylogenetic incongruence were found among loci. Putative clonal relationships among genotypes were estimated, showing a mixture of large clonal complexes and unrelated singletons. Discordance between the nuclear ribosomal rRNA and other gene genealogies is consistent with introgression of ribosomal RNA alleles of phylogenetic species FSSC 9 into F. keratoplasticum. No significant population subdivision based on clinical versus non-clinical sources was found. Incongruent phylogenetic trees and the presence of both mating types within otherwise identical STs were observed, providing evidence for sexuality in F. keratoplasticum. Cryptic speciation suggested in a published three-locus MLST system was not supported with the addition of new loci, but evidence of introgression of ribosomal RNA genes from another strongly supported phylogenetic species (FSSC 9), also known from plumbing systems and human infections, was detected in two isolates. Overall, F. keratoplasticum is a diverse and geographically unstructured species with a mixed clonal and recombinant life history.