Full Length Research Paper
Biological activity of Streptomyces noursei against ochratoxin A producing Aspergillus niger Nanis G. Allam1*, Abd El-Raheem R. El-Shanshoury1,3, Hamdy A. Emara2 and Amira Z. Zaky1 Microbiology Unit, Botany Department, Faculty of Science, Tanta University, Tanta, 31527, Egypt. Microbiology Department, Soil, Water and Environment Institute, Agriculture Research Center, Giza, Egypt. 3 Biotechnology Department, Faculty of Science, Taif University, P. O.Box 888 Taif 21974, Kingdom of Saudi Arabia. Accepted 28 October, 2011
Aspergillus niger isolated from some common medicinal and herbal plants used in Egypt, was found to be producer for ochratoxin A. This research investigate the biological control of ochratoxin A production by A. niger, using some bacterial isolates belonging to true bacteria (Bacillus pumilus), Lactic acid bacteria (Lactobacillus acidophilus, Lactobacillus bulgaricus and Lactobacillus plantarum) and Actinomycete isolates numbered 1, 2, 3, 4, 5, 6 and 7, that proved variable antagonistic activity against A. niger. The Actinomycete isolate number 3 was the most effective and identified as Streptomyces noursei. The optimal conditions for antifungal production by S. noursei were performed on starch nitrate medium at pH 7 after 7 days of growth at 30°C. The active antifungal substance(s) were separated, semi purified and characterized as a protein substance. The semi purified substance inhibited spores formation, thinned the conidiophores and deformed both strigmata and conidial heads. Key words: Aspergillus niger, Streptomyces noursei, ochratoxin A.
INTRODUCTION Growing mould may produce toxic secondary metabolites, such as mycotoxins. Among hundreds of fungal secondary metabolites are mycotoxins which include aflatoxins (AFL), deoxynivalenol, fumonisins (FB), ochratoxin A (OTA), and zearalenone. They are of major health concern for humans and domestic animals (Miller, 1994). Mycotoxins can enter into the human food chain directly through foods of plant origin and indirectly through foods of animal origin (Kovacs, 2004). Many types of food products in the markets have been reported to be contaminated with AFL or metabolites of AFL. These include tree nuts, peanuts, figs, melon seed, pumpkin seed, sesame seed, sunflower seed, lotus seed, coix seed, red pepper, white pepper, nutmeg, paprika, mixed spices, rice, corn, mixed cereals, chilies, and copra (Wilson, 2002). OTA has been found in many cereals, raisins, cocoa products, green coffee beans, wine, soybeans, grape juice, pork sausages (Pittet, 2001), spices, and herbs (Patel et al., 1996). Ueno et al. (1991) were the first to report on ochratoxin A production by a black Aspergillus species, Aspergillus foetidus. This was later confirmed by Téren et al. (1996) and Magnoli et al. (2003). Abarca et al. (1997) reported that two strains of Aspergillus niger produced OTA, and confirmed in numerous studies (Abarca et al., 2003; Suarez-Quiroz et al., 2004). Horie (1995) reported OTA in Aspergillus carbonarius, and confirmed by Heenan et al. (1998), Varga et al. (2000), Abarca et al. (2003) and Sage et al. (2004). Biological control means the use of living agents to control pests or plant pathogens and offers an important alternative to synthetic chemicals. The use of bacteria like Pseudomonas sp. and Bacillus sp., have been investigated due to their properties to produce antifungal metabolites and protect plants from fungal infection (Siddiqui et al., 2005; Nourozian et al., 2006). Biological control is being increasingly considered by the scientific community as a reliable alternative to pesticide utilization in field and in post-harvest. This biological approach is highly desirable for controlling fungal growth on grapes, helping to...