Isolation and characterization of marine actinomycetes – bioprospecting for antimicrobial, antioxidant and anticancer properties

The novel therapeutic agents are frequently produced from marine actinomycetes and are still being explored due to their vast diversity. In this research, we isolated �ve marine actinomycetes (BN01, BN12, BN13, BN14 and GB15) from the soil sediments of The morphological and physicochemical properties of the isolates were characterized. The 16S rRNA sequencing analysis showed that the isolates were belonging to two genera namely Streptomyces and Saccharopolyspora. The extracellular crude secondary metabolites were extracted from the culture �ltrate of all the marine actinomycetes isolated and tested for the antimicrobial, antioxidant and anticancer potential adopting standard methods. The results revealed that the extracts of the isolates BN01, BN14, and GB15 exhibited antimicrobial activity against M. luteus, E. coli, and S. aureus, with the maximum zone of inhibition of 19 mm, 21 mm, and 27 mm respectively, at the concentration of 10 mg/mL. The extract of the isolate BN12 showed excellent radical scavenging activity of 97.75 % at the concentration of 60 µg/mL and has the half-maximal inhibitory concentration (IC 50 ) of 8.66 µg/mL. The anticancer activity results showed that the extract of the isolate BN12 had better inhibitory activity against the MCF 7 cell line with the IC 50 value of 261.01 µg/µL. of aerial and substrate mycelium of the actinomycetes was observed in four different media, namely M2, M3, M4, and M5. [M2- Yeast Extract-Malt Extract agar; (Yeast extract- 4g, Malt extract- 10g, Dextrose- 4g, Sea water- 1000mL, pH- 7.3, Agar- 20g); Trace salts solution (For the preparation of M3, M4, M5 and M7) FeSO 4 . 7H 2 O- 0.1g, MnCl 2 2 O- 0.1g, ZnSO 4 2 O- 0.1g, Distilled H 2 O- 100mL;M3- Oatmeal agar (Oatmeal- Sea water- Agar- 18g, salts- 1mL); M4- salts-Starch agar Starch- Sea water- mL; Solution-II K HPO (anhydrous)- MgSO NaCl- (NH 2 CaCO Trace salts solution- mL; Sea water- mL, pH- Agar- 20g); The solution-I (starch suspension) and the solution-II (salts solution) were mixed and autoclaved at 121°C for 15–20 min; M5-Glycerol-asparagine agar (L-Asparagine- 1g, Glycerol- 10g, Anhydrous K 2 HPO 4 – 1g, Trace salts solution- 1 mL, Sea water- 1000mL, Agar- 20g, pH- 7.0-7.4). BN14, and GB15 streaked onto the Petriplates and incubated for 2 at The colour of mycelium Tresner-Backus colour series Yellow, Blue, Gray, colour of the aerial and the substrate mycelium. The production of soluble pigments and melanin pigment was observed by using Peptone-Yeast Extract Iron agar (Peptone iron agar (dehydrated)- 36g, Yeast extract- 1g, Sea water- 1000mL, pH- 7- 7.2) and Tyrosine agar medium (Glycerol- 15mL, L-tyrosine- 0.5g, L-asparagine- 1g, Anhydrous K 2 HPO 4 − 0.5g, MgSO 4 ·7H 2 O- 0.5g, NaCl- 0.5g, FeSO 4 ·7H 2 O- 0.01g, Trace salts solution- 1 mL, pH- 7.2–7.4, Sea water-1000mL ,Agar- 20g)(Shirling and Gottlieb Acetic acid- 100mL) to the cultures in nitrate broth (Peptone- 5g, Beef extract- 3g, KNO 3 - 1g, NaCl- 30g, Sea water- 1000mL pH- 7.0 ± 0.2). The formation of pinkish-red colour after the addition of reagents was positive. A few drops of twenty volumes of hydrogen peroxide were added to seven day old colonies of selected isolates grown on Bennett's agar medium, which resulted in the evolution of oxygen with air bubble formation on the surface of the colonies determined as catalase positive. Oxidase production was determined by the addition of broth culture on the oxidase disc (HiMedia, India). The formation of blue colour within 30 seconds was scored as positive (Williams et al. oval-shaped short-chain spores. and mycelium, as production of soluble and melanin in six different M2, M3, M4, M5, M6 and M7, and revealed that the colour varied from white, grey, yellow, brown, red, pink, green, and black. Similar results were shown by (Ramachandran 2019) as the mycelial colour varies from brown, yellowish brown, light grey, dark grey, and white. It also showed that the actinomycetes isolate had not produced any soluble pigments and melanin. isolate BN01 showed excellent growth at 4% NaCl, whereas BN12 showed at 2% NaCl. At concentrations 2, 4, and 6% NaCl, the isolates BN13 and BN14 have moderate and maximum growth tolerance, respectively. The isolate GB15 has good growth at 10% NaCl. These results were compared with (Valan et al. 2012) where all the marine actinomycetes isolated from sediment showed good growth at 2% NaCl, moderate growth at 4%, less growth at 6%, and no growth at 8% NaCl. All the isolates have degraded the organic compounds hypoxanthine and tyrosine except BN12, and except BN13, all isolates have degraded casein. But no isolates have degraded xanthine or adenine. Most of the isolated actinomycetes were dependent on glucose, fructose, lactose, galactose, maltose, sucrose, and as a carbon source. The isolate GB15 does not utilize maltose, galactose, inositol or rhamnose. various line MCF-7 with the IC 50 value of 261.01 µg/µL. The GC-MS pro�ling of ethyl acetate crude extract of Streptomyces sp. strain BN12 revealed 10 compounds with biological activity and some with no reports. The results shows that the marine actinomycetes are potential source of bioactive compounds.