Antibacterial and antioxidant aryl-enclosed macrocyclic polyketide from intertidal macroalgae associated heterotrophic bacterium Shewanella algae
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Previously unreported aryl-enclosed 12-membered macrocyclic polyketide characterised as 2′-[(8-ethyl-8-methyl-2,5-dioxo-1-oxacyclododecanyl)methoxy]-methyl benzoate, was identified from the organic extract of Shewanella algae, a heterotrophic gamma proteobacterium, isolated from an intertidal marine macroalgae Hypnea valentiae. The titled macrocyclic polyketide displayed potential antibacterial activity (minimum inhibitory concentration 3.75 µg/mL) compared to that exhibited by chloramphenicol (6.25 µg/mL). Potent antioxidant activity of the studied compound was characterised by its greater scavenging effects on 2,2-diphenyl-1-picrylhydrazyl radical and 2,2′-azino-bis-3-ethylbenzothiozoline-6-sulfonic acid (IC50 0.59 and 0.53 mg/mL, respectively) compared with standard, α-tocopherol (IC50 > 0.65 mg/mL). In silico molecular docking studies of the polyketide with the penicillin binding protein active sites encoded in methicillin resistant Staphylococcus aureus core genome displayed lesser binding energy of −10.31 kcal/mol, which could be correlated with its in vitro antibacterial activities. Structure-activity correlation studies demonstrated the direct relationship of electronic and optimum hydrophobic properties of the macrocyclic polyketide with its bioactivities. Therefore, the presently studied aryl-enclosed macrocyclic compound could be utilised as potent antioxidant and antibacterial pharmacophore in the medicinal formulations.
KeywordsShewanella algae Heterotrophic gamma proteobacterium Hypnea valentiae Macrocyclic polyketide Antibacterial activity Structure-activity correlation studies
This work was supported by funding under Kerala State Council for Science, Technology and Environment (Grant No. 040/FSHP-LSS/2014/KSCSTE). The authors are thankful to Indian Council of Agricultural Research, New Delhi for providing facilities to carry out the work. The authors thank the Director, Central Marine Fisheries Research Institute and Dean, Faculty of Marine Sciences, Lakeside Campus, Cochin University of Science and Technology for support. Thanks are due to the Head, Marine Biotechnology Division, Central Marine Fisheries Research Institute for facilitating the research activities.
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Conflict of interest
The authors declare that they have no conflict of interest.
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