title: A cysteine/methionine auxotroph of the opportunistic fungus Aspergillus flavus is associated with host-range restriction: a model for emerging diseases.
abstract: The evolution of host specialization in pathogens is a topic of considerable interest, particularly since it can represent a decisive step in the emergence of infectious diseases. Aspergillus flavus is an opportunistic fungus capable of infecting a wide variety of hosts, including plants, insects and mammals, although with low virulence. Here the derivation of an A. flavus strain that exhibits severe host restriction is reported. This strain exhibited a severe diminution or a complete lack of conidial production on a variety of standard agar media and on various plant species. However, it retained its ability to infect insects from various orders and to re-emerge from and adequately conidiate on the insect cadavers as a culmination of the pathogenic life cycle. This strain, demonstrating insect-dependent conidiation, was discovered to be a cysteine/methionine auxotroph due to an inability to reduce sulfate to sulfite. However, other A. flavus auxotrophs tested for plant and insect host range failed to show insect-dependent conidiation. An association between this specific auxotroph and a decreased host range is shown, emphasizing the role of nutrition in the host-pathogen relationship with respect to host restriction and evolution towards obligate pathogenesis.
authors.affiliation: Department of Biological Sciences, 500 Glenridge Avenue, Brock University, St Catharines, Ontario, Canada L2S 3A1.
authors.forename: Lisa R
authors.initials: LR
authors.lastname: Scully
authors.affiliation: Department of Biological Sciences, 500 Glenridge Avenue, Brock University, St Catharines, Ontario, Canada L2S 3A1.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Bidochka
mesh_terms: D000818:Animals; D001228:Aspergillosis / Q000382:microbiology; D001231:Aspergillus flavus / Q000235:genetics / Q000254:growth & development* / Q000472:pathogenicity*; D003470:Culture Media; D003545:Cysteine; D007814:Larva / Q000382:microbiology; D007915:Lepidoptera / Q000254:growth & development / Q000382:microbiology; D000455:Medicago sativa / Q000382:microbiology; D008715:Methionine; D008969:Molecular Sequence Data; D025282:Mycelium / Q000254:growth & development; D013045:Species Specificity; D014774:Virulence
chemical_list: D003470:Culture Media; D008715:Methionine; D003545:Cysteine