Introduction: Antibiotic resistance is rising dramatically worldwide. Thus, the production of new antibiotics is indispensable. Recent scientific efforts have been aimed at the bioprospecting of microorganisms' secondary metabolites, with special emphasis on the search for antimicrobial natural products derived from endophytes. Endophytes are microorganisms that inhabit the internal tissues of plants without causing apparent harm to their host. Currently, it is strongly believed that all types of plant species do anchorage endophytic bacteria (EB). The natural therapeutic compounds produced by EB do have several potential applications in medicine, agriculture and pharmaceutical industry. To investigate antibacterial properties, in this study, Actinobacteria were isolated from Chamomile sp., identified and bioprospected by morphological and molecular methods. Methods: Samples were collected from Ilam and then divided into roots, leaves, stems and flowers. After disinfection, they were cut into 2 mm pieces and cultured on casein agar culture medium and incubated at 28 ºC for up to four weeks. Using PCR method targeting 16S rRNA gene, identification of Actinobacteria was carried out. To evaluate the antibacterial properties of the isolated Actinobacteria, the agar diffusion method was used. In parallel, frequencies for the presence of biosynthetic gene clusters, polyketide synthase- (PKS-) I, PKS-II, and nonribosomal peptide synthetase (NRPS) among isolated Actinobacteria were determined. Results: Ninety bacteria were isolated from different parts of chamomile flowers. It was determined that 47 bacteria (52.22%) of these bacteria belong to the phylum Actinobacteria. and out of 47 bacteria, 15 isolates (31.91%) had antibacterial properties. Of these, 12 isolates (80%) exhibited antibacterial effects against Staphylococcus aureus, 2 isolates (13.33%) against Pseudomonas aeruginosa, 3 isolates (20%) against Escherichia coli and 2 isolates (13.33%) against Salmonella typhi. The results of molecular analysis of NRPS, PKS-I and PKS-II genes showed that out of 47 isolated Actinobacteria strains, 20 isolates (42.55%) had NRPS gene, 6 isolates (12.76%) had PKS-I gene and 23 isolates (48.93%) had PKS-II gene. Discussion & Conclusion: This study indicates that Chamomile sp. has a number of active Actinobacteria that produce secondary metabolites with antibacterial properties. Hence, this medicinal plant can be a valuable source for the isolation of Actinobacteria with the potential of producing new antibiotics.
