An endophytic Streptomyces sp. DARP-7 isolated from coastal lichen and enhancement of its antibacterial metabolite production using response surface methodology

Actinomycete DARP-7 was isolated from the coastal foliose lichen Dirinaria aegilita (Afzel.ex Ach.) B.J.Moore and identified as Streptomyces sp. using 16S rRNA sequencing. Among the eight culture media used for anti-microbial metabolite production, the peptone yeast extract iron medium (ISP-6) showed higher production with the maximum zone of inhibition (12 mm) against Staphylococcus aureus. Further, the ISP-6 medium components were optimized through the Plackett-Burman design (PBD) followed by Response Surface Meth-odology (RSM). Yeast extract, sodium thiosulphate, and ferric ammonium citrate would play a significant role in antibiotic production. Further, the significant variables from PBD were optimized through Central Compos-ite Design (CCD) of RSM for enhanced antibiotic production. The optimal medium components were found to be peptone-15 (g/L), protease peptone -5 (g/L), yeast extract -2.915 (g/L), ferric ammonium citrate -0.651 (g/L), K2HPO4 -1 (g/L) and Na2S2O3- 0.155 (g/L), respectively. The optimized result was validated and the antibacterial activity against S. aureus increased upto 19.9 mm (66.7%). The resazurin dye based quantifica-tion of minimum inhibitory concentration of the DARP-7 crude extract was found to be 41.34 mg and 46.44 mg against S. aureus and E.coli, respectively. Further, the compound profiling was done using UV-VIS, FTIR, EEM and GC-MS confirming the presence of polyene conjugates. Thus, the study delivers coastal lichen could be promising source for isolating bioactive metabolites producing rare actinobacteria. Furthermore, the use of a statistical optimization tool to improve bioactive metabolite yield is discussed.(c) 2022 SAAB. Published by Elsevier B.V. All rights reserved.

Automated summary

The actinomycete DARP-7 was isolated from a coastal foliose lichen and the culture medium components were optimized to enhance antibiotic production. Compound profiling confirmed the presence of polyene conjugates. The study suggests that coastal lichens could be a promising source for bioactive metabolites producing rare actinobacteria.