Taxonomical study on the causative bacterium of spotting disease of sea urchin Strongylocentrotus intermedius

An identification of the causative bacterium strain 12-N, which was isolated from coelomic fluid of diseased sea urchin Strongylocentrotus intermedius, was undertaken based on its cultural and biochemical properties, DNA base composition, and DNA-DNA homology. The strain 12-N was an aerobical Gram-negative filiform, which formed bright yellow pigmented colony and showed slightly gliding motility without flagella. Its morphology gradually changed from filiform to short rods during incubation in liquid medium. Its optimum growth temperature was considered to be between 25 degrees C and 30 degrees C and no growth was observed above 37 degrees C or below 10 degrees C. The strain required seawater for its growth and could not degrade agar, cellulose or chitin. The G+C mol% of DNA from the strain was 40.5. On the basis of these characteristics, it is considered that the strain 12-N belongs to the genus Flexibacter and closely resembles F. maritimus. However, the strain differed from F. maritimus in serological property and DNA-DNA homology.