Isolation and evaluation of antibacterial activity of Actinobacteria from donkey manure

Microbial products play an important role in digestion and absorption of substances, increase immunity and disease resistance. These products are abundantly produced by Actinobacteria. The aim of this study was to isolate Actinobacteria, to investigate the antibacterial properties and to identify the genes that produce bioactive compounds from donkey manure. For this purpose, donkey manure samples were cultured on the casein stretch medium, then Actinobacteria isolates were identified by PCR and their antibacterial properties were investigated by agar well diffusion method. These isolates were also screened for PKS I, PKS II and NRPS genes. Of 92 Actinobacterial isolates, 66 isolates had antagonistic activity against test bacteria. Of these, 61 isolates (92%) inhibited Staphylococcus aureus, 45 isolates (68%) Escherichia coli, 47 isolates (71%) Bacillus cereus and four isolates (6%) inhibited Pseudomonas aeruginosa. The results of molecular analysis of PKS I, PKS II and NRPS genes for 30 isolates of Actinobacteria selected from the 92 isolates showed that 18 isolates (54%) contained NRPS gene, seven isolates (23%) enclosed PKS I gene and nine isolates (30%) contained PKS II gene. The results of this study indicate that donkey manure is rich in Actinobacteria producing bioactive compounds with antibacterial properties and contain a significant percentage of PKS I, PKS II and NRPS genes.