Manikkam Radhakrishnan

A study of the bactericidal, anti-biofouling, cytotoxic and antioxidant properties of actinobacterially synthesised silver nanoparticles.

Actinobacteria- mediated synthesis of silver nanoparticles (AgNPs) is a reliable, eco-friendly and important aspect of nanobiotechnology. In this study, aqueous silver ions, which were exposed to an actinobacterial biomass of Streptomyces naganishii (MA7), were reduced to form stable AgNPs under optimised conditions. The microbially synthesised AgNPs were characterised by UV-Vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), atomic force microscopy (AFM) and high- resolution transmission electron microscopy (HR-TEM). The size (5-50 nm) and shape (spherical) of the AgNPs were determined. The biosynthesised AgNPs exhibited good bactericidal, anti-biofouling, antioxidant and cytotoxic effects with regards to the HeLa cell line. A single protein band with a molecular weight of 44 kDa was obtained after partial purification of the culture filtrate via polyacrylamide gel electrophoresis. The potent actinobacterial strain was identified by its molecular (16s rRNA sequencing), phenotypic and cultural characteristics. The current study demonstrated the potential use of the extremophilic actinobacterial strain of S. naganishii (MA7) as a novel source for AgNPs synthesis with improved biomedical applications.

Characterization and phylogenetic analysis of antituberculous compound producing actinomycete strain D25 isolated from Thar Desert soil, Rajasthan.

During the course of the anti-infective drug discovery programme, actinomycete strain D25 was recovered from the Thar Desert soil, Rajasthan, India. Actinomycin type of compound isolated from the strain D25 showed promising activity against multi drug resistant and extensively drug resistant M. tuberculosis isolates. The present study reports the characteristics and phylogenetic status of the actinomycete strain D25. Phenotypic and cell wall characteristics revealed that the strain belongs to the genus Streptomyces. Further 16s rRNA analysis confined the genus Streptomyces with 97% similarity to the closely related species Streptomyces althioticus KCTC 9752. The 16s rRNA sequence was submitted to GenBank with the accession number JN604533.1. According to Bossard et al. (2003) strain D25 was found to be a novel species of the genus Streptomyces from Thar Desert soil, Rajasthan.

Bioactive potential of actinobacteria isolated from certain under-studied regions in India -

The present study reports the bioactive potential of actinobacteria isolated from certain under-studied regions in India. Soil and sediment samples and mangrove leaves were collected from 16 different under-studied regions in India. Actinobacteria was isolated by adopting selective isolation methods. Totally 158 actinobaterial cultures were selected from the collected terrestrial, marine and plant samples. More number of colonies was isolated from magnesite area, Kolli Hills and forest area in Himachal Pradesh. Majority of the isolates produced powdery (40%) and leathery (25%) colonies with white (38%) or Gray (37%) colour aerial mycelium.Bioactive compound from all the isolates were produced by agar surface fermentation and its activity was tested by agar plug method against S. aureus, E. coli and C. albicans. About 64 out of 158 cultures showed antibacterial activity in which 62 cultures was active against S. aureus whereas 26 were active against E. coli. Twenty three actinobacterial cultures were exhibited antifungal activity. About 11 actinobacterial cultures were active against both S. aureus and E. coli. In antifungal testing whereas fourteen actinobacterial cultures were found to be active against S. aureus, E. coli and C. albicans. Maximum of 21 antibacterial cultures and antifungal cultures were obtained from Magnesite soil followed by 12 antibacterial and 7 antifungal cultures were obtained from the soil sample collected from Himachal Pradesh.This evidenced that the under-studied ecosystems in India are the promising source for bioactive actinobacteria with broad spectrum antibacterial and antifungal activity. Further studies on the potential actinobacterial strains result in the isolation of broad spectrum antimicrobial metabolites.