Light-emitting bacteria from the Caspian Sea, North of Iran

Bioluminescence is the production and emission of light by living organisms. This phenomenon occurs widely in different organisms. In fact, light-emitting bacteria are the most abundant and widespread luminescent organisms found in marine, freshwater and terrestrial habitats. In this study, the sea water samples were collected from the Caspian Sea, North of Iran. Luminous colonies were observed after an overnight incubation at 25°C on nutrient sea water complete medium. One luminous bacterium isolated, identified and named as Vibrio sp. isolate Caspian based on biochemical tests and 16S rRNA gene sequencing. Besides, two genes involved in bioluminescence, luxA and luxB were sequenced. Light emission measurement was performed for this bacterium  using luminometer, then compared with a control sample previously isolated from water samples in south of Iran. Vibrio sp. Caspian had a weak light emission in comparison with control sample. Sequencing result of 16S rRNA, luxA, and luxB genes showed that these sequences were highly similar to V. vulnificus. However, there were some difference in both nucleotide and amino acid sequences of luciferase. Phylogenetic analysis based on luciferase nucleotide sequences also showed high degree of relationship between the present tested Vibrio and other related species. In general, the present study revealed the capability of indigenous marine sources of Iran for providing bioluminescent bacteria with different characteristics which may result in finding new luminous systems with various applicable capacities