Microbial interaction of Aspergillus parasiticus and Bacillus subtilis with Alternaria alternata. Production of alternariol, alternariol mono- methylether and tenuazonic acid on sunflower seeds. M. Etcheverry*, L. Cavaglieri and S. Chulze. Departamento de Microbiologfa e Inmunologfa, Facultad de Ciencias Exactas Ffsico Qufmicas y Naturales. Universidad Nacional de Rfo Cuarto. Rfo Cuarto, C6rdoba, Argentina. *Address for correspondence: Dra. Miriam Etcheverry. Departamento de Microbiologfa e Inmunologfa, Facultad de Ciencias Exactas, Ffsico Qufmicas y Naturales. Universidad Nacional de Rfo Cuarto. Ruta 36 Km 601 (5800). Rfo Cuarto, C6rdoba, Argentina. Tel.54-058-676113-Fax:058- 680280-E mail: Metcheverry @exa.unrc.edu.ar Abstract Production of alternariol, alternariol mono-methylether and tenuazonic acid by Alternaria alternata was studied in competition with Aspergillus parasiticus and Bacillus subtilis on irradiated sunflower seeds at 0.90 aw. In cultures co-inoculated with Alternaria alternata and Aspergillus parasiticus alternariol production decreased by 64%. Similar results were observed in cultures co-inoculated with Alternaria alternata and Bacillus subtilis. Introduction Contamination of agricultural products with filamentous fungi presents economic and sanitary problems due to the potential of mycotoxins. These toxic metabolits may be transferred to animals and man through the foodstuffs and feedstuffs. At present, the role of mycotoxins in ecological systems have not been elucidated. Mycotoxins can be produced by particular fungi to inhibit the growth of other species or to protect the latter against predation. The study of biological interactions in ecological niches as in food, could allow likelihood of mycotoxin production by toxigenic fungi in a competitive environment to be predicted. The genus Alternaria includes saprophytic species that are commonly isolated from a wide range of substrates. A. alternata is the fungal species most frequently isolated from sunflower seeds in which it may produce alternariol (AOH), alternariol mono- methylether (AME) and tenuazonic acid (TA) among other mycotoxins (1, 2, 3). The optimal conditions of water activity and temperature for AOH, AME and TA production by Alternaria alternata in sunflower seeds were 0,90a at 25-~ respectively (4, 5, 6). Aspergillusflavus and Aspergillus parasiticus were the main species isolated most frequently from Argentinian sunflower seeds after Alternaria alternata. Also, aflatoxin 2