Isolation, characterization and biotechnological potential of tropical culturable rhizospheric fungi from four mangrove species in Kenya

Fungi play important roles, as both decomposers and plant symbionts in mangrove ecosystems. Their ability to survive extreme environmental conditions makes them potential rich sources for recovery of novel bioactive compounds. In this study, biotechnological potential of fungi recovered from the rhizospheres of four mangrove species (Sonneratia alba, Rhizophora mucronata, Ceriops tagal and Avicennia marina) was explored. Rhizospheric sediment samples of the mangroves were collected using standard protocols and different media used for isolation of fungi. A total of 33 fungal isolates were recovered and characterized based on morphological, physiological and Internal transcribed spacer (ITS) gene region analysis. The disk diffusion method was used to evaluate the antibacterial activity of the isolates. Morphologically, the isolates showed different characteristics with regard to color, margin and elevation. Physiologically, all the isolates were able to grow at different pH ranges, ranging from pH 4 to pH 12 and at different temperatures from 20 to 30°C and tolerated sodium chloride up to 7%. Phylogenetic analysis grouped the isolates into two phyla: Ascomycota and Basidiomycota affiliated to different genera; Penicillium, Aspergillus, Talaromyces, Diatrypella, Thielavia, Hypocreales, Paracremonium, Geosmithia, Peniophora, Massarina and Fulvifomes. A total of 17 representative isolates produced inhibition zones against three pathogenic bacterial strains. The findings demonstrate that the tropical mangroves rhizospheres are a rich source of fungi with antibacterial compounds and traits relevant for biotechnological application.   Key words: Antimicrobial activity, tropical marine fungi, Mangrove sediments, Internal transcribed spacer (ITS).