Deletion of the Delta12-oleic acid desaturase gene of a nonaflatoxigenic Aspergillus parasiticus field isolate affects conidiation and sclerotial development

Abstract

Aims: 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. Methods and Results: We disrupted A. parasiticus D12-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 (DodeA), 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 DodeA mutants produced less conidia than the parental strain on all media. Linoleic acid supplementation (as sodium linoleate at 0AE3 and 1AE2 mg ml )1 ) restored the DodeA 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 DodeA mutants were unable to produce sclerotia on CVN. On unsupplemented PDA and CZ, DodeA 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 DodeA 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. Significance and Impact of Study: 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.

Effects of different substrates and oils on aflatoxin B1 production by Aspergillus parasiticus

“…The values are in agreement with those supplied in the tables of feed composition and nutritive values in China (2013, 24 edition), in which the fat contents of soybean, corn, and wheat are 17.3-18.7, 3.1-5.3, and 1.7 g/100 g, respectively [28], whereas that of peanut is 48.7 g/100 g [29]. According to Chang et al [30] and Wilson et al [31], oil-rich crops are often infested with toxigenic fungi. Lillehoj et al [32] reported previously that ground, autoclaved corn and full-fat corn germ were excellent substrates, while defatted germ was the poorest substrate for toxin production.…”

“…Chang et al [30] and Wilson et al [31] that high-oil crops are often infested with toxigenic fungi. In addition, seed oil mainly consists of fatty acids, such as palmitic acid (C16:0), stearic acid (C18: 0), oleic acid (C18: 1), linoleic acid (C18: 2), and linolenic acids (C18: 3), among which oleic and linoleic acids are the most common unsaturated fatty acids [39][40][41].…”

Characterization of the Aspergillus parasiticus Δ12-desaturase gene: a role for lipid metabolism in the Aspergillus–seed interaction

“…It was consequently defective in rates of spore germination, colony growth and development. In a parallel study, a DodeA mutation that was generated in an Omethylsterigmatocystin-accumulating strain of A. parasiticus, SRRC 2043, also resulted in altered conidiation and sclerotial development (Chang et al, 2004). This supports our conclusion that the reduction in conidiation and abolishment of sclerotial production seen for DApodeA compared to the wild-type is due solely to aberrant polyunsaturated fatty acid metabolism and serves to emphasize the genetic connection between fatty acid metabolism and fungal development.…”

Microarray analysis of transcript accumulation during perithecium development in the filamentous fungus Gibberella zeae (anamorph Fusarium graminearum)

“…The fatty acid composition of sexual tissues of Neurospora differs substantially from the composition of asexual tissues, such changes in fatty acid composition correlate with the sexual stage of development, and mutations in the gene encoding the b-fatty acid synthase affect sexual development (GoodrichTanrikulu et al 1998). Precocious sexual inducers (psi factors), a family of structurally related oleic-and linoleic-acid-derived oxylipins, have been shown to alter the ratio of asexual to sexual sporulation in the filamentous fungus A. nidulans (Calvo et al 2001;Chang et al 2004;Tsitsigiannis et al 2005). It is also known that the formation of lipid bodies increases in saprophytic fungi with the formation of reproductive structures (Losel and Sancholle 1996).…”