Natural Red Pigment With Antibacterial Activity From Nigrospora Sphaerica CL-OP 30, An Endophytic Fungus Isolated From Leaf Of Swietenia Macrophylla King
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Date
2016-03
Authors
Iu, Chai Woei
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Publisher
Universiti Sains Malaysia
Abstract
The demand for natural pigment from microbial sources are growing rapidly since most of the synthetic pigments are found to be hazardous to mankind, and most of the natural pigments obtained from other natural sources are insufficient for the industrial purposes. In this study, six endophytic fungal isolates which were isolated from Swietenia macrophylla were selected as the preliminary study subjects where Nigrospora sphaerica CL-OP 30 was eventually selected as the sole target for the study as the fungus produced highest yield of reddish pigment at day 14 with the 0.1471 OD/g of production compared to others. The higher pigmentation was favourable when the fungus was cultivated in light condition without the incorporation of host plant extract with the ideal inoculum size of the fungus, 2 fungal plugs with 1cm in diameter. The red-pigmented ethyl acetate extract from the fermentative broth exhibited significant antibacterial activity against all eight Gram positive bacteria tested where the inhibition zone ranged from 16.0 ± 1.0 – 25.7 ± 3.1 mm whilst the MIC ranged from 93.75 – 375.00 μg/mL. The time-kill assay showed that the antimicrobial activity of the extract against Bacillus cereus (clinical isolate) and Staphylococcus aureus (foodborne isolate) were concentration-dependent. The results from the Scanning Electron Microscopy study shows the extract made the cells of B. cereus and S. aureus shrunken, crumpled, dented, pitted, or even burst. The EC50 of DPPH free radical scavenging activity of the extract was determined to be 157.5725 μg/mL while the average of total phenolic content in the extract was 82.77638 μg GAE/mg. On the bioautography study, only one orange-coloured spot with Rf value at 0.682 showed antibacterial activity. Using open column chromatography, fraction F2 with bright orange colour was separated and found to be the only active fraction with antibacterial activity by exhibited inhibition zone ranged from 19.7 ± 1.2 mm to 23.0 ± 1.0 mm, while the MIC ranged from 31.25 – 125.00 μg/mL. The GC-MS analysis could not detect any natural pigment compounds. The presence of the other fatty acids and phenylethanol as the antibacterial compounds were detected. The brine shrimp cytotoxicity test indicated that the crude extract was chronically toxic whilst fraction F2 exhibited both acute and chronic toxicity. Based on the studies, the fraction F2 possessed greater antibacterial activity compared to the crude extract from N. sphaerica CL-OP 30. LC-MS is recommended in future study of natural pigment. the pigmented compounds from N. sphaerica CL-OP 30 have great potential to be explored as the colouring agent with antibacterial activity.
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Keywords
Pigment