BIOLUMINESCENT SYMBIONTS OF FLASHLIGHT FISHES AND DEEP-SEA ANGLERFISHES FORM UNIQUE LINEAGES RELATED TO THE GENUS VIBRIO

BIOLUMINESCENT symbioses range from facultative associations to highly adapted. apparently obligate ones1. The family Anomalopidae (flashlig ht fishes) encompasses five genera of tropical reef fishes that have l arge suborbital light organs2. The suborder Ceratioidei (deep-sea angl erfishes) contains 11 families. In nine of these, females have a biolu minescent lure3,4 that contains bacterial symbionts5. In all other fis h light-organ symbioses (occuring in 10 families in 5 orders6), the sy mbionts belong to three Photobacterium species7; nonsymbiotic luminous bacteria are Vibrio species8. The bacteria are extracellular and tigh tly packed in tubules that communicate with the exterior7, releasing b acteria into the gut of the host or the surrounding sea water. The rel eased bacteria are usually cultivable and can contribute to planktonic populations9,10. Although anomalopids release bacteria9 and ceratioid s have pores that would allow release, the fate of these bacteria is u nknown and they cannot be cultured by standard isolation techniques. W e report here phylogenetic analysis of 16S ribosomal RNA gene sequence s from light organs that show that anomalopid and ceratioid symbionts are not known luminous bacteria, but are new groups related to Vibrio spp. They are characterized by host specificity, deep divergence betwe en symbionts from different genera (anomalopids) or families (ceratioi ds) and, possibly, parallel divergence of hosts and symbionts.