Screening of streptomyces isolates from mau forest comple for antimicrobial activity against selected plant pathogens

Abstract

The search for new principles in bio-control of plant pathogens different from the classical fungicides is of worldwide interest. The genus Streptomyces is the producer of about 80% of all known world antibiotics. It is of a major interest in bio control of plant pathogens. The study consisted of three steps: (i) collection of soil samples from different sites in the Mau Forest Complex and isolation of Streptomyces from these samples, (ii) screening for antimicrobial activity of the isolates against selected plant pathogen in the laboratory i.e. Fusarium moniliforme and Ascochyta rabie; Erwinia carotovora, Xanthomonas campestris and Pseudomonas savastanoi pv. phaseolicola and other indicator reference cultures which were : Staphylococcus aureus ATCC 25923; Escherichia coli ATCC2 5922; Pseudomonas aeruginosa ATCC 27853 and Bacillus subtilis ATCC 6633. (iii) Identification of the isolates most effective in inhibiting the growth of the pathogens. A total of 270 isolates were screened for antimicrobial activity, 14 of the isolates showed antibacterial activity against the test bacteria while 39 isolates had antifungal activity. Most of the selected isolates had more effective inhibitions to fungal plant pathogens than bacterial plant pathogens. Ethyl acetate extracts of culture filtrates from the isolates produced significantly different (P<0.05) inhibitory effects to some of the tester microorganisms. Five of these isolates that had both antifungal and antibacterial activity were identified using molecular methods. Out of these isolates, isolate WHF2B16 was identified as treptomyces Mau 1 (Accession numberKR780774), isolate BFOR3B14 as Brachybacterium Mau 1 (Accession number KR476396), these two isolates belong to the phylum actinobacteria. Two bacterial isolates belonged to the genus Bacillus; isolate WHF3A15 as Bacillus subtilis strain and WHF1A17 as Bacillus Mau 1 (Accession number KR780775), finally isolate BFOR1B22 was identified as uncultured Acinetobacterium. The study found that soils from Mau Forest complex harbor diverse group of bacteria including Streptomyces species that could be exploited for control of plant diseases. There is need to establish their effectiveness in green house and field studies