ASEXUAL DEVELOPMENT IN AN AFLATOXIGENIC STRAIN OF ASPERGILLUS PARASITICUS

The biochemical and physiological events that accompany asexual development in an aflatoxigenic strain of Aspergillus parasiticus have been investigated. The growth of the fungus was followed by the incorporation of {('3)H}amino acids into TCA insoluble protein. The growth curve displays a lag, exponential and stationary phase. Competence time is dependent on the inoculum size. At an initial inoculum level of 1.4 x 10('4) conidia/ml the competence time is 8.1 hr compared with 22.6 hr at an initial inoculum level of 3 x 10('2) conidia/ml. The acquisition of competence is partially dependent on the completion of a protein synthesis function whose RNA synthesis function is completed before germination. The inducibility of nitrate reductase is transient and declines coincidentally with a rapid uptake of glucose from the medium. The loss of inducibility of nitrate reductase between 25 and 35 hr occurs well after the establishment of competence at 8.1 hr at an initial inoculum level of 1.4 x 10('4) conidia/ml. Laccase activity is conidiation dependent and absent in vegetative mycelia of the strain studied. There is no quantitative relationship between specific activity of laccase and the number of conidia produced. Aflatoxin production is greatest in cultures that do not sporulate and do not produce laccase activity. The time of initial aflatoxin accumulation is independent of sporulation.;The volatile fraction of carrot seed oil (VCSO), limonene and terpinene inhibit aflatoxin production and result in elevated final pH of culture broths. The addition of VSCO inhibits mycelial weight compared to limonene and terpinene which do not affect the mycelial weight. The inhibitory activity against aflatoxin production by VCSO, limonene and terpinene is repressed at an initial pH of 5 or greater.;The synthesis of aflatoxin is not the result of asexual development. The biochemical and physiological events that occur during the development of A. parasiticus are very similar to published reports for other Aspergilli. Further work is needed to elucidate the physiological role of aflatoxin.