title: Deletion of the Delta12-oleic acid desaturase gene of a nonaflatoxigenic Aspergillus parasiticus field isolate affects conidiation and sclerotial development.
abstract: OBJECTIVE
  To investigate how linoleic acid affects conidial production and sclerotial development in a strictly mitotic Aspergillus parasiticus field isolate as related to improving biocompetitivity of atoxigenic Aspergillus species.
  
  
  RESULTS
  We disrupted A. parasiticusDelta12-oleic acid desaturase gene (odeA) responsible for the conversion of oleic acid to linoleic acid. We examined conidiation and sclerotial development of SRRC 2043 and three isogenic mutant strains deleted for the odeA gene (DeltaodeA), either with or without supplementing linoleic acid, on one complex potato dextrose agar (PDA) medium and on two defined media: nitrate-containing Czapek agar (CZ) and Cove's ammonium medium (CVN). The DeltaodeA mutants produced less conidia than the parental strain on all media. Linoleic acid supplementation (as sodium linoleate at 0.3 and 1.2 mg ml(-1)) restored the DeltaodeA conidial production comparable to or exceeding the unsupplemented parental level, and the effect was medium dependent, with the highest increase on CVN and the least on PDA. SRRC 2043 and the DeltaodeA mutants were unable to produce sclerotia on CVN. On unsupplemented PDA and CZ, DeltaodeA sclerotial mass was comparable to that of SRRC 2043, but sclerotial number increased significantly to two- to threefold. Supplementing linoleic acid to media, in general, tended to decrease wild type and DeltaodeA sclerotial mass and sclerotial number.
  
  
  CONCLUSIONS
  Linoleic acid stimulates conidial production but has an inhibitory effect on sclerotial development. The relationship between the two processes in A. parasiticus is complex and affected by multiple factors, such as fatty acid composition and nitrogen source.
  
  
  CONCLUSIONS
  Conditions that promote sclerotial development differ from those required to promote maximum conidial production. Manipulation of content and availability of linoleic acid at different fungal growth phases might optimize conidial and sclerotial production hence increasing the efficacy of biocompetitive Aspergillus species.
authors.affiliation: Southern Regional Research Center, Agricultural Research Service, US Department of Agriculture, New Orleans, LA 70124, USA. pkchang@src.ars.usda.gov
authors.forename: P-K
authors.initials: PK
authors.lastname: Chang
authors.forename: R A
authors.initials: RA
authors.lastname: Wilson
authors.forename: N P
authors.initials: NP
authors.lastname: Keller
authors.forename: T E
authors.initials: TE
authors.lastname: Cleveland
mesh_terms: D001230:Aspergillus / Q000235:genetics*; D003470:Culture Media; D044943:Fatty Acid Desaturases / Q000235:genetics*; D017353:Gene Deletion; D005800:Genes, Fungal / Q000235:genetics*; D005822:Genetic Vectors / Q000235:genetics; D019787:Linoleic Acid / Q000235:genetics; D009154:Mutation; D025282:Mycelium / Q000235:genetics; D013172:Spores, Fungal / Q000235:genetics
chemical_list: D003470:Culture Media; D019787:Linoleic Acid; D044943:Fatty Acid Desaturases; C040448:delta-12 fatty acid desaturase