Isolation and characterization of Photobacterium phosphoreum from migrating Alaskan salmon

Abstract

We isolated luminous bacteria from drying chum salmon, Oncorhynchus keta, reported by Alaska native fishermen to be 'glowing in the dark.' The salmon were harvested for subsistence use from the Yukon River, Alaska. We identified our luminous bacterial isolates as Photobacterium phosphoreum based on nutritional versatility, and 16S rDNA and luxA gene sequences. P. phosphoreum has previously only been isolated from the marine environment. We tested whether our strains, isolated from fish harvested in freshwater, represent cold-adapted, freshwater-tolerant strains of P. phosphoreum. We also analyzed lux operon composition and organization, and examined the 5' promoter region of the lux operon for shared genes and regulatory elements from strains of P. phosphoreum from Alaska, the Black Sea, Oregon, and from near the Canary Islands. Our results indicate our P. phosphoreum strains have a lower optimal growth temperature than other strains but rapidly lose viability after inoculation into river water. Analyses of the P. phosphoreum lux operon reveal a striking pattern of conservation of composition and organization, and suggest there is conservation in the location of the transcriptional start among geographically separated strains of the same species.