Antimicrobial Activity of Streptomycetes Isolated from the Mau Forest Complex in Kenya

Abstract

Search for newprinciples in biocontrol of plant pathogens different from the classical fungicides is of worldwide interest. Members of the genus Streptomyces are known to produce about 80% of all known antibiotics in the world. These antibiotics have beenapplied in medicine, veterinary and in agriculture. Presumptive Streptomyces from the Mau Forest Complex were isolated from soils obtained from different sites within the Mau Complex. 270 isolates were screened for antimicrobial activity against selected plant pathogenic bacteria and two fungal plant pathogens i.e. Erwinia carotovora, Xanthomonas campestris pv. campestris, Pseudomonas savastonoi pv. phaseolicola, Fusarium moniliforme, Ascochyta rabie; the reference cultures were: Staphylococcus aureus ATCC25923; Escherichia coli ATCC 25922; Pseudomonas aeruginosa ATCC 27853 and Bacillus subtilis ATCC 6633. 14 (0.05%) of the isolates showed antibacterial activity against the test bacteria while 39 (0.14%) isolates had antifungal activity. 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 had both antifungal and antibacterial activity. There were further characterized using biochemical, microscopy and morphological methods. These methods showed that they were Gram positive and had similarities to members of the genus Streptomyces. 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.