Abstract:
Mangrove sediment associated bacteria are of significant importance in the field of medicine and pharmaceuticals as new promising sources of biologically active pharmacophores due to extreme conditions, such as high salt concentrations and soil anoxia. This study aimed to evaluate the antimicrobial, antioxidant and antiinflammatory properties of Bacillus amyloliquefaciens associated with Acanthus ilicifolius and Avicennia officinalis, collected from the Mangalavanam mangrove ecosystem of Kerala State of India. The bacteria exhibiting significant antioxidant and antimicrobial activities were isolated, identified and characterized by integrated biochemical, morphological, microbiological and 16S rRNA sequencing. Spot-overlawn-assay was carried out to screen all the 40 isolates against various pathogens like A. caviae, E. coli, V. parahemolyticus and MRSA to hit upon the antibacterial compound producing microbes. The B. amyloliquefaciens MK765025 strain exhibiting significant antimicrobial activity against V. parahemolyticus and antioxidant activity against the free radicals, was selected for further extraction and purification of bioactive metabolites. The extraction of bioactive compounds was carried out using ethyl acetate to obtain the crude organic extracts and exhibited potential antioxidant activities (i.e., IC50 3.5 µg/mL and 3.9 µg/mL to quench DPPH and ABTS radical species, respectively) coupled with 5-lipoxygenase inhibitory activity (IC50 6 µg/mL). The extracellular organic extracts exhibited potential activity towards the test pathogens V. parahemolyticus, MRSA, E. coli and A. caviae with the inhibition zone ranging from 16-22 mm for 100 µg of the extract in disc diffusion assay. The minimum inhibitory concentration was determined by broth dilution method against different pathogenic bacteria, and was found to be lesser than 12.5 µg for all the test organisms. The crude extract of B. amyloliquefaciens MK765025 exhibited significant antimicrobial, antioxidant and anti-inflammatory activities, and therefore, was selected for purification on C18 reverse stationary phases to yield two polyketides with oxotetrahydrofuran moiety. The compound (2) displayed potential antioxidant activities (IC50 0.31-0.32 mg/mL) and anti-inflammatory properties against pro-inflammatory lipoxygenase (IC50 0.90 mg/mL). Thus the compound 2, could find its utilities as valuable pharmacophore with potential antioxidant and antiinflammatory properties.
