Dynamics of deoxynivalenol and zearalenone production by Fusarium graminearum under laboratory conditions

Toxicological investigations encompassed two cultures of Fusarium graminearum: (i) D2 isolate, originating from air was obtained on Sabouraud medium during a routine control of laboratory sterility conditions at the Department of Microbiology of the Center for Bio-Ecology in 2006, and (ii) GZ-LES control isolate, a well known producer of zearalenone (ZON) and deoxynivalenol (DON), was isolated from maize kernel collected at Leskovac in 1975. Preliminary analysis of fungal potential for the production of DON and ZON were performed by the modified rapid screening method of Filtenborg et al. (1983). Dynamics of DON and ZON biosynthesis was tested under different conditions of isolate cultivation: (i) in a basic liquid semi-synthetic medium with 2% yeast extract and 15% sucrose, pH 6.5 (YES), (ii) in broth with same concentrations of yeast extract and sucrose supplemented with 0.23 mg/l ZnSO4 x 5 H2O, pH 6.5 (YESZn) and (iii) on natural solid substrates such as wet sterilized maize and rice kernels. The quantitative determination of DON and ZON was performed in both liquid and natural solid substrates with thin-layer chromatographic methods (TLCs). The maximum yield of DON was recorded after three weeks of cultivation on maize kernels at 27±1°C. Contrary to the D2 isolate, which did not show the potential for the DON biosynthesis, the control isolate GZ-LES produced 645.6 ppb of the same type B trichothecene under previously mentioned conditions. The ZON biosynthesis by the isolate D2 (1.2 ppb) was observed after 2 weeks of the stationary cultivation in YES and YESZn at room temperature (17-19°C). The same isolate produced 0.74 ppb and 17.35 ppb ZON on maize and rice kernels after only 7 and 28 days of cultivation at the room temperature ranging from 17 to 19°C and from 15 to 23°C, respectively.