| Antarctic ecosystems are extreme environments to study the biodiversity, survival and adaptation of bacteria. The current study describes the rich and diverse heterotrophic bacterial communities from seasonally ice-free open lakes in East Antarctic Schirmacher Oasis and a perennially ice-covered Lake Joyce in West Antarctic McMurdo Dry Valleys using culture-dependent and culture-independent approaches. Heterotrophic bacteria from three different Phyla: Proteobacteria, Bacteroidetes and Actinobacteria were cultured from lakes of Schirmacher Oasis using 16S rRNA gene-based taxonomic analysis. However, similar approach applied on the community DNA of the Black Hole sediments in Lake Joyce exhibited previously undescribed heterotrophs from seven different phyla: Proteobacteria, Planctomycetes, Bacteroidetes, Candidate Division OP10, Verrucomicrobia, Chloroflexi and Gemmatimonadetes.;The results of DNA-DNA hybridization, physiological and biochemical tests allowed characterization of a proposed new species, Janthinobacterium schirmacherense strain Ant5-2T from a pro-glacial Lake Podprudnoye in Schirmacher Oasis. An overall framework of the structure and function of a constitutively expressed cold shock protein, CspD from Ant5-2 T was established. In silico analysis and in vitro DNA binding assay revealed that CspD forms a highly stable domain-swapped dimer and binds to ssDNA, suggesting its RNA-binding property necessary for cold adaptation. Further, vioA of the operon vioABCD involved in the biosynthesis of purple violet pigment (PVP) from Ant5-2 was identified, cloned and sequenced. A non-pigmented vioA mutant strain was obtained following mini-Tn10 transposon mutagenesis that exhibited significantly reduced survival compared to the wild-type upon exposure to UV suggesting the role of PVP in UV tolerance in Ant5-2.;The PVP also proved to be a broad spectrum compound possessing antimycobacterial and anticancer activities. The minimum inhibitory concentration (MIC) of PVP for virulent M. tuberculosis H37Rv strain was 34.4 ìg/ml suggesting that it could be used to develop a potent drug against tuberculosis. Further, the chemotherapeutic potential of PVP against murine UV-induced 2237 fibrosarcoma and B16F10 melanoma and mechanism by which it inhibits the cell cycle progression and induces apoptosis was determined. This study encompasses an overview of the rich heterotrophic microbial communities thriving in extreme Antarctic environment, their survival strategies and how they can benefit mankind.;Keywords: Antarctica, Janthinobacterium sp. Ant5-2, Cold shock protein D, purple violet pigment, antimycobacterial, anticancer. |
