The name Flexibacter maritimus is proposed for a group of 15 bacterial strains isolated from diseased red sea bream (Pagrus major), black sea bream (Acanthopagrus schlegeli), and rock bream (Oplegnathus fasciatus). These bacteria grew in cytophaga medium prepared with seawater but failed to grow in cytophaga medium supplemented with NaCl. The isolates were gram-negative, flexible rods which exhibited gliding motility on wet surfaces. They did not utilize agar, cellulose, or chitin. The mean guanine-plus-cytosine content of the deoxyribonucleic acids of eight selected strains was 31.8 & 0.4 mol%. Strain R2 (= NCMB 2514) is designated the type strain of the new species.A Flexibacter infection was first described by Masumura and Wakabayashi (13) as the cause of mortality (20 to 30%) among the fry (15 to 60 mm) of red sea bream (Pagrus major) and black sea bream (Acanthopagrus schlegeli) reared in seawater at a net-cage culture facility in Hiroshima Prefecture, Japan. Affected fish had eroded mouths, frayed fins, and tail rot. In the lesions large numbers of long, slender bacterial rods were observed, giving the infected tissue a pale-yellow appearance. Since 1976, this disease has become a common problem among red and black bream fry cultured at various locations in Japan. During the winter, Flexibacter infections have also caused mortality among cultured fish, with lesions occurring initially as greyish-white cutaneous foci on the fins, head, and trunk. On the skin, the lesions become eroded, and shallow ulcers are produced. The organisms isolated from the diseased fish were characterized by Hikida et al. (6) and Wakabayashi et al. (18). In this paper, we present evidence that a group of 15 bacterial isolates from diseased red sea bream, black sea bream, and rock bream (Oplegnathus fasciatus) constitute a new species, for which we propose the name Flexibacter maritimus.
MATERIALS AND METHODSBacterial strains. The 15 bacterial strains used in this study and the sources from which they were isolated are given in Table 1. These bacteria were obtained from diseased fish by streaking portions of external lesions or kidney tissues onto cytophaga agar (1) containing 70% seawater. After incubation at 25°C for 2 to 3 days, pale-yellow, flat, irregular colonies with uneven edges appeared.Morphology and growth studies. Cell morphology was recorded from light microscope observations of Gramstained smear preparations. Motility was determined by examining wet mounts with a phase-contrast microscope. Microcyst formation was tested by the method of Dworkin and Gibson (5).The optimum growth temperature was determined by use of a temperature gradient incubator (model TN-3; Toyo Kagaku Sangyo Co.). The ability of the strains to grow in the following media was tested: cytophaga broth containing 0, 1, 3, 5 , 7, or 10% NaCl and cytophaga broth made up with 0, 10, 30, 70, or 100% seawater. The requirement for inorganic salts was determined by inoculating media containing vari-
