In-vitro antibacterial activity of coral reef associated bacteria and optimization of bioactive metabolite production.

This study reports the antibacterial activity of coral reef associated bacteria against bacterial pathogens and optimization of metabolite production. Twelve morphologically different bacterial were isolated from stony coral reef collected from Rameshwaram coastal area, Tamil Nadu. Cell free supernatant of all the bacterial isolates were tested against Staphylococcus aureus, Bacillus cereus, Salmonella typhi, Escherichia coli, and Klebsiella pneumoniae by agar well diffusion method. Of the 12 isolates tested, seven isolates showed antibacterial activity again at least one of the test organisms with the zone of inhibition in the range of 9-14 mm. The antibacterial compounds were extracted from the cell free supernatant using ethyl acetate and tested for antibacterial activity. In diffusion method, crude extract from strain RC12 showed 11-17 mm inhibition against all the test pathogens and the same was selected for optimization studies. Effect of culture conditions and medium components such as different carbon, nitrogen, mineral, pH, temperature on antibacterial metabolite production was studied by adopting one-factor-at-a- time method. The metabolite production was influenced by lactose, ammonium sulphate, K2HPO4 while the optimal cultivation conditions were pH 7 and 37°C. The potent strain RC12 was identified as Pseudomonas sp based on their phenotypic and biochemical characteristics. The finding of the present study concludes that coral reef bacteria found to be the best source for bioactive metabolites with broad spectrum activity.

Antibacterial and antifungal activities of Actinobacteria isolated from Rathnagiri hills.

This study was performed to isolate actinomycete colonies having antibacterial and antifungal activity from soil samples. A total of 27 actinomycete colonies were isolated in pure culture from five soil samples using Starch casein agar medium. Entire isolates were screened for their antimicrobial activity by agar plug method against five each of human pathogenic bacteria and fungi. Of this, 7 strains inhibits B. substilis, 3 strains inhibits Klebseilla sp, 6 strains inhibits B. cerus, 5 strains inhibits S. aureus and only 2 strains inhibits E. coli. Incase of fungi all the actinobateria has moderate activity with less fungal strains, only 1 strain (RA 5) inhibits entire fungus except Penicillium sp. The metabolites from potent strain was produced by fermentation, separated by centrifugation, it was tested for their antimicrobial activity against the test bacterial and fungal strains by well diffusion and disc diffusion method. In this study, the metabolites from RA5 (identified as Streptomyces sp.) have showed good antibacterial and antifungal activity. Since many isolates showed inhibitory activity against indicator bacteria, it is suggestive that Rathnagiri hill’s soil could be an interesting source to explore for antibacterial secondary metabolites.

Exploitation of bacteria from forest ecosystem for antimicrobial compounds.

This study deals with bacterial prospecting from forest soil with special reference to antimicrobial substances. Total of 25 morphologically different bacterial colonies were isolated from soil samples collected from Anaimalai forest and Parambikulam tiger reserve forest, Western Ghats, India. About 12 (48%) out of 25 isolates showed antibacterial activity in which strain AF1 showed inhibitory activity against more number of test pathogens. Bioactive substance from strain AF1 was produced by adopting submerged fermentation and extracted using ethyl acetate and chloroform. In disc diffusion method, ethyl acetate extract showed good antibacterial activity (9-17 mm zone of inhibition). Active fraction present in the ethyl acetate extract was determined by thin layer chromatography based bioautography. Findings of this work supported that the forest ecosystems investigated in this study will be potential place for bacterial bioprospecting.