Abstract

Members of the actinobacteria phyla are widely distributed in a multiplicity of natural environments: terrestrial, aquatic and extreme environments from tropical to polar regions. They play significant roles in several processes that contribute to soil fertility, such as nutrient cycling, decomposition of various compounds like complex biopolymers, and formation of beneficial soil humus. Actinobacteria comprise several different genera, the Streptomyces genus has attracted great interest due to its well known ability to synthesize many different bioactive secondary metabolites, including more than 80% of known antibiotics, antitumor compounds and growth effectors. Antarctic microorganisms, especially the psychrophiles and psychrotrophs, develop novel metabolic pathways as a result of the evolutionary selection to survive and grow under these extreme conditions. The aim of this study was to phylogenetically and physiologically characterize an Antarctic Streptomyces strain and test the activity of bioactive compounds against foodborne pathogens and MCF-7 (breast cancer), PC-3 (prostate cancer) and HT-29 (colon cancer) cell lines. The taxonomic status of the isolate was established using a polyphasic approach. The strain was identified as belonging to the genus Streptomyces based on the scanning electron microscopic observation and partial 16S rRNA gene sequence analysis. The phylogenetic tree analysis revealed that Streptomyces strain fell into the same subclade with S. fildesensis and S. purpureus. The similarity analysis showed that it is closely related to Streptomyces fildesensis (99.8%), Streptomyces purpureus (97.2%) and Streptomyces beijiangensis (98.1%). This Streptomyces strain was observed to be psychrotolerant according to growing parameters, optimum temperature (30 ºC, μ=0,762) and maximal temperature (37°C, μ=0.0336) of growth, slightly halotolerant (up to 5% of NaCl) and tolerant to a wide pH range of 5.0–12.0. The bioactive compounds production was higher at 12°C than at 28°C. Bioactive compounds are capable of inhibiting the growth of 7 foodborne pathogens and showed significant activity against cancer cell lines.The LC 50 value of bioactive compounds recovered for the Control OKF6-TERT2, Control Colon cell, MCF-7, PC3 and HT-29 cell lines were 73.46, 28.02, 19.54, 18.16, and 6.618 μg/ml, respectively. In conclusion, the Antarctic Peninsula, even though some areas are occupied by human, remains as a largely unexploited source of cold-adapted microorganisms capable of producing valuable bioactive compounds. The current study described a promising psychrotolerant Antarctic Streptomycete that might be a potential source of genes encoding for antimicrobial compounds and enzymes with medical applications.