SULFUR-OXIDIZING SYMBIONTS HAVE NOT CO-EVOLVED WITH THEIR HYDROTHERMAL VENT TUBE WORM HOSTS - AN RFLP ANALYSIS

A fine-scale phylogenetic comparison was made among the symbionts of d ifferent genera of hydrothermal vent tube worms. These included Riftia pachyptila and Tevnia jerichonona, which inhabit sites along the East Pacific Rise, and Ridgeia piscesae from the Tuan de Fuca Ridge. An an alysis of restriction fragment length polymorphism (RFLP) was employed using three symbiont-specific gene probes: eubacterial 16S rRNA, RuBP C/O Form II, and ATP sulfurylase (recently cloned from the Riftia symb iont). Results indicated that all of the symbionts from the three diff erent hosts were conspecific and the Riftia and Tevnia symbionts were indistinguishable over an 1800-km range. Significantly, this indicates that the symbionts have not co-evolved with their respective hosts, w hich are known to belong to separate families. This study strongly sup ports the conclusion that the symbionts are acquired de novo by each g eneration of juvenile tube worms from a common source in the surroundi ng seawater.