EXPLOITATION OF SOIL AND RHIZOSPHERE INHABITING FUNGAL SPECIES FOR BIOLOGICALLY ACTIVE SECONDARY METABOLITES
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Date
2015
Journal Title
Journal ISSN
Volume Title
Publisher
Center of Biotechnology
Abstract
In quest for new bioactive compounds the present study deals with isolation,
identification and bioassay screenings of fungi and purification and structural elucidation of pure
compounds isolated from fungal strains under study. For production of fungal bioactive
secondary metabolites fungal strains were isolated from soil and rhizosphere of Mentha piperita
using Potato Dextrose Agar (PDA) and Sabouraud Dextrose Agar (SDA) media. After
preliminary antimicrobial testing, two fungal strains were selected for metabolites production,
their bioassays and subsequent structural characterization. The rhizospheric strain was identified
as Aspergillus specie while soil isolate was identified to be Penicillium specie. For secondary
metabolites production both fungal strains were cultured in Czapec Yeast Broth (CYB) medium
at 28 oC for 14 days at 150 rpm. Crude secondary metabolites produced by fungal strains were
then extracted and tested for their respective bioassays. In our study fungal metabolites were
tested for five different activities i.e. antibacterial, antifungal, cytotoxic, phytotoxic and
herbicidal activities.
In antibacterial bioassay crude extracts of Aspergillus and Penicillium species were
tested against eight pathogenic bacterial strains i.e. Xanthomonas oryzae, Klebsiella pneumonia,
Bacillus subtilus, Proteus vulgaris, Staphylococcus aureus, Escherichia coli, Salmonella typhi
and Shigella flexeneri. A dose concentration from 1 to 500 μL mL-1 of the crude extracts was
tested against pathogenic bacterial strains and zone of inhibition was recorded in millimeters
(mm). A dose concentration of 500 μL mL-1 of ethyl acetate extract of Aspergillus sp. inhibited
growth of all test bacterial strains but the highest zones of inhibition were recorded against B.
subtilus (47.5 mm) and S. flexeneri (45 mm) while lowest zone of inhibition was recorded
against X. oryzae (9 mm). At 500 μg/mL of ethyl acetate extract of Penicillium sp growth of P.
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vulgaris, E. coli, S. aureus, B. subtilus and S. flexeneri was inhibited by forming zones of 34, 28,
24, 23 and 21 mm respectively. Lowest zone of inhibition was recorded against S. typhi (9.5 mm)
while considerable inhibition was noted against K. pneumoniae (16 mm) and X. oryzae (13 mm)
at 500 μL mL-1 of Penicillium sp. extract.