Effect of iron on resuscitation of Tenacibaculum sp., the causative bacterium of spotting disease of short-spined sea urchin Strongylocentrotus intermedius, from the viable but non-culturable (VBNC) state

Tenacibaculum sp., the causative bacterium of spotting disease of short-spined sea urchin Storongylocentrotus intermedius, has been known to enter into the viable but non-culturable (VBNC) state in 75% Herbst's artificial seawater at 5 degrees C. Previous studies indicated that elevation of water temperature or addition of iron induced the resuscitation of the bacterium from the VBNC state. The present study revealed that the resuscitation period from the VBNC state was further prolonged when Tenacibaculum sp. in the VBNC state was resuscitated under the presence of iron, catalase and the homogenate of the sea urchin. Environmental waters around a sea urchin hatchery in Hokkaido, Japan often contained iron at concentrations over 0.34 mg/L in summer. The infection experiment showed that the VBNC cells activated with iron produced the spotting disease to healthy sea urchins. These results suggest that the VBNC cells of Tenacibaculum sp. resuscitated during summer under iron-rich environment are associated with outbreaks of the disease.