Journal of Food, Agriculture & Environment, Vol.7 (1), January 2009 219 www.world-food.net Journal of Food, Agriculture & Environment Vol.7 (1) : 219-223. 2009 WFL Publisher Science and Technology Meri-Rastilantie 3 B, FI-00980 Helsinki, Finland e-mail: info@world-food.net Effect of some bioagents on growth and toxin production of Aspergillus flavus Link Saleh A. Kabli Department of Biological Sciences, Faculty of Science, King Abdulaziz University, P.O. Box: 80203, Jeddah, Saudi Arabia. e-mail: sakabli@yahoo.com Received 3 October 2008, accepted 9 December 2008. Abstract The extracts of Aspergillus niger, Lactobacillus lactis and Nigella sativa seeds as aflatoxin and growth inhibitors of Aspergillus flavus were screened. Minimal inhibitory (MIC) and minimal fungicidal (MFC) concentrations of the extracts were determined. N. sativa seeds extract showed a higher inhibitory effect than the other two bioagents extracts. The results show that N. sativa extract inhibits growth and aflatoxin production, which may be due to a reduction in lipid biosynthesis in the toxin producing cultures. The correlation between versicolorin A accumulation and aflatoxin biosynthesis by A. flavus Link was also discussed. It could be of significant importance as bio-preservatives in the prevention and control of aflatoxin production. Key words: Bioagents, Aspergillus flavus, aflatoxin inhibitors, versicolorin A. Introduction Aflatoxin (AF) is one of the mycotoxins produced by some strains of Aspergillus flavus, Aspergillus nomius and Aspergillus parasiticus. Aflatoxin has been reported in many food and feed raw materials 1, 3-5, 39 . Food contaminated with AF poses a serious health threat when consumed by humans and animals. The toxin has been reported to be carcinogenic, teratogenic and hepatotoxic 10, 12, 14 . The increased demand for safe and natural food, without chemical preservatives, provokes many researchers to investigate the antimicrobial effects of natural compounds. Besides the pure chemicals, some plants and microbes or their active metabolites have been introduced as inhibitors of aflatoxin biosynthesis by the producing fungi 42 . Despite that, the majority of known AF inhibitors suffer from a large limitations concern to their harmful effects on eukaryotic systems at effective concentrations which highlight the need for search about new active principals. Numerous investigations have confirmed the antimicrobial action of different biopreservatives in model food system and real food 25, 34, 35 . Nigella sativa is an annual herbaceous plant; seeds are black in color and taste slightly bitter. They are frequently used as a spice and added as a flavoring agent to bread, pickles and other dishes 3 . The seeds of the plant are extensively used in traditional medicine in some countries, for the treatment of several diseases 29 . Recent scientific investigations on the seeds and their oil indicated a number of pharmacological activities including anticarcinogenic 37 , antiulcer 16 , antibacterial 24 , antifungal 18 , anti-inflammatory, antipyretic and analgesic 2 . In this study, the effects of Aspergillus niger, Lactobacillus lactis and N. sativa seed extracts on growth and AF production by A. flavus Link were evaluated. Materials and Methods Bioagents: Local strains of A. niger and Lactobacillus lactis were kindly provided by the Microbiology Section, Faculty of Science, King Abdulaziz University. Seed oil of Nigella sativa were used to study their inhibition effect on growth and aflatoxin producing strain of A. flavus Link. Antifungal analysis: Antifungal analysis and determination of the minimal inhibitory (MIC) and minimal fungicidal (MFC) concentrations, and fungicidal kinetics of the bioagents extracts were performed. The disc diffusion method was used for antifungal screening as follows: Sterile Sabouraud Dextrose Agar (Merck) was inoculated with A. flavus Link spores (10 6 spores/ml) and distributed into Petri plates of 70 mm diameter. Whatman No.1 sterile filter paper discs (6 mm) containing 5 l and 15 l from each of the tested extracts were placed on the agar plates. The plates were incubated at 28±2°C for 10 days. Three replicates were used for each treatment. Diameters of inhibition zones were measured using Vernier calipers. The percentage of mycelial inhibition was calculated by the equation: I = 1-T/C×100 [where I is the inhibition (%), C is the colony diameter from a control Petri plate (mm) and T is the colony diameter from a test Petri plate (mm)] was used. MIC and MFC 32 were determined by broth dilution method as follows. Various concentrations of the bioagent extracts were added to 5 ml of YES broth tubes containing 10 6 spores/ml. The tubes were then incubated in incubator shaker as to evenly disperse the extracts throughout the broth in tubes. The highest dilution (lowest concentration), showing no visible growth, was regarded as MIC. Cells from the tubes showing no growth were sub-cultured on Sabouraud Dextrose Agar plates to determine if the inhibition was reversible or permanent. MFC was determined as the highest dilution (lowest concentration) at which no growth occurred on the plate.