International Centre For Genetic Engineering And Biotechnology, India
Title: Actinobacteria from forest ecosystems of India: Antimicrobial and biosynthetic potential for polyketides and nonribosomal peptides discovery
Priyanka Sharma is a National Post-Doctoral Fellow in India. Research is her passion. She has expertise in isolation, characterization and screening of actinobacteria from diverse sources with the aim for clinical use as antinfective drugs. During her Ph.D., she has screened more than hundred actinobacteria for the production of antimicrobial metabolites against human disease causing drug-resistant bacteria and fungi. Screening of antibiotic biosynthetic genes responsible for the production of these antimicrobial metabolites is also a part of her research. Besides Streptomyces, she has also isolated members of rare actinobacteria genera. For the first time, she has reported a phenolic compound, 3,5-bis(1,1-dimethylethyl)-phenol, as antimicrobial agent produced by Nocardia sp. PB-52 (GenBank accession number KM406386). Presently, she is screening endophytic actinobacteria for ex vivo and in vivo antiplasmodial activity against chloroquine-sensitive and resistant strains of Plasmodium falciparum causing malaria in humans. Besides research, she is also actively involved in an NGO that looks after old age homes.
Actinobacteria are the leading producers of useful natural products such as polyketides, nonribosomal peptides and alkaloids of medical and industrial importance. The objective of the study was to investigate the in vitro antimicrobial potential and biodiversity of a collection of actinobacteria from forests of Northeast India and explore its potential use as a novel source of polyketides and nonribosomal peptides. For the isolation of actinobacteria, soil samples were collected from two forest ecosystems, namely, Pobitora Wildlife Sanctuary and Kaziranga National Park located in the North-eastern part of India (Figure 1). Northeast India, with its unique asset of rich biodiversity, is a part of Indo-Burma mega biodiversity hotspot. A total of 100 actinobacteria were isolated using different selective media. During the antimicrobial screening of actinobacteria against ten test microbial pathogens, including drug-resistant pathogens, 77 actinobacteria exhibited promising antimicrobial activity. 16S rDNA sequencing of the representative actinobacteria comprised of Streptomyces, Nocardia and Kribbella sp. Further screening revealed that PKS-I genes were detected in 4 actinobacteria and their amino acid sequences shared 55-68% similarity with their closest BLASTP matches relating to gene product involved in the production of tautomycin, oligomycin, rifamycin, etc. PKS-II genes were detected in 15 isolates with 68-95% sequence similarity with their closest BLASTP matches at amino acid level. Their closest match pathway products were predicted as compounds belonging to different groups of aromatic polyketides such as naphthoquinone, anthracycline, angucycline, glycosides etc. NRPS genes were detected in only 2 isolates with 40-53% sequence similarity to their closest relatives at the amino acid level and their pathway products were analyzed as virginiamycin and oxazolomycin. Lower sequence similarity (>70%) to the closest relative suggested the novelty of these genes resulting in the possibility of novel compounds. The partial PKS-I, PKS-II, NRPS and 16S rRNA gene sequences have been deposited in GenBank database. The overall findings of the present study emphasize the importance of exploration of biodiversity hotspots like forest ecosystems for the isolation of actinobacteria producing bioactive compounds with diverse biological activities.