BACKGROUND AND OBJECTIVES: Luminescent bacteria are a unique group of microorganisms that emit visible light due to specific biochemical reactions. The Caspian Sea, as one of the largest enclosed water areas, offers an interesting ecosystem to discover these luminous creatures. The aim of this study was to isolate, identify and molecularly investigate the luminescent bacteria of the Caspian Sea. Samples were collected from 23 shore and offshore areas from all over the Caspian Sea in northern Iran. MATERIALS AND METHODS: The samples were inoculated in SWB liquid culture medium and kept in an incubator at 28°C for 24 hours. Then it was transferred to the SWA agar culture medium to isolate the luminescent bacteria. The luminescent colonies were selected through the emission of visible light in a dark room. After examining the isolates in terms of morphology and physiology, 5 isolates were selected for molecular identification. Molecular identification of luminescent isolates was done by sequencing analysis of 16S rRNA gene using polymerase chain reaction and phylogeny tree of isolates was drawn. RESULTS AND DISCUSSION: In the present study, 19 luminescent bacteria, including MAZ1-MAZ19, were isolated. All the isolates were gram-negative and in terms of morphology, they were rods, bent rods and short rods. the results of molecular analysis of 16S rRNA gene showed that isolates MAZ1, MAZ4, MAZ5, MAZ8 and MAZ12 have 98.75, 96.99, 99.76, 99.44 and 98.29% respectively with Vibrio mediterranei, Vibrio rotferianus, Photobacterium leiognathi, Aliivibrio fscheri and Photobacterium mandapamensis had homology. The luminescence of these isolates was blue, blue, blue-green, green, and blue-green, respectively, and their luminescence intensity was 22, 16, 15, 16, and 38 million RLU. these results provide valuable insight into the presence and diversity of light-emitting bacteria in the Caspian Sea. The study of these microorganisms contributes to our understanding of bioluminescence and may have applications in biotechnology and environmental monitoring.
