Cytotoxic and Antimicrobial Potential of Actinomycete Species Saccharopolyspora salina VITSDK4 Isolated from the Bay of Bengal Coast of India

Abstract

Problem statement: Although the diversity of marine Actinobacteria have been studied and biotechnologically exploited throughout the world, the studies on marine actinobacteria in Indian peninsula are largely unexplored. Of 9 maritime states in India, only 4 states have been extensively studied for the diversity of actinobacteria. Further, the studies on bioactive actinomycetes from saline soil are very scanty. In the present study, we had taken an initiative to isolate culturable halophilic actinomycetes and to screen the bioactive potential. Approach: The marine sediment sample was collected at a depth of 400 cm at Marakkanam. The strain was isolated using ISP No. 2 medium supplemented with 25% sea water. The polyphasic taxonomy of the strain was evaluated by phenotypic, chemotaxonomic and phylogenetic analysis. The 16S rRNA was sequenced and phylogenetic relationship with the closest related species were studied. The growth conditions and the medium had been optimized under shake-flask conditions by measuring the dry weight of the mycelium. The isolate was subjected to fermentation and the crude extract was screened for cytotoxic, hemolytic and antimicrobial activity. The cytotoxicity was evaluated on HeLa cells by MTT assay, hemolytic assay on mouse erythrocytes and the antimicrobial activity was determined by agar diffusion assay. Results: Based on polyphasic taxonomy the species was identified as Saccharopolyspora salina and belongs to the genus Saccharopolyspora. The 16S rRNA sequence of the isolate showed 100% similarity with Saccharopolyspora salina. Based on the phylogenetic and phenotypic evaluation the isolate was designated as Saccharopolyspora salina VITSDK4. The growth was maximal in the designed production medium with the incubation temperature of 28°C and pH of 7.4. It is a moderately halophilic species requires 9% NaCl concentration for optimal growth. The cytotoxicity on HeLa cells showed the IC₅₀ value of 26.2 μg mL^-1 by MTT assay. The hemolytic activity on mouse erythrocytes showed the EC₅₀ value of 266 μg mL^-1. The crude extract also exhibited significant antagonistic activity against fungal pathogens Aspergillus niger, Aspergillus fumigatus, Candida albicans and the Gram negative bacteria Escherichia coli and Klebsiella pneumoniae. Only moderate activity was seen against Gram positive bacteria Staphylococcus aureus and Bacillus subtilis. Conclusion/Recommendations: Based on the results of our investigation, the isolated strain was identified as Saccharopolyspora salina VITSDK4, which was moderately halophilic, produces an extracellular bioactive metabolite, which inhibits the proliferation of HeLa cells as well as antagonistic to fungal and bacterial pathogens. Further studies on purification and characterization of the pure compound from the strain were ongoing. The results of this study suggested that the marine actinomycetes from the unexplored Indian coast could provide lead compounds of therapeutic value.