Flexibacter sp., a gliding bacterium pathogenic to some marine fishes in Japan

A new bacterial disease, bringing about mass mortality of cultured juvenile red sea bream (Pagrus major) and black sea bream (Acanthopagrus schlegeli) in Hiroshima Prefecture, was found to be due to a kind of gliding bacterium. In the present study, 8 strains of gliding bacteria isolated from diseased juvenile red sea breams and black sea breams were studied on their morphological, biochemical, and physiological characteristics. All strains were gram-negative, flexuous rods which exhibited gliding motility without flagella, and usually about 0.5μm by 2 to 30μm. Filamentous cells measuring up to 100μm in length were occasionally found. The organisms showed no anaerobical growth and did not produce microcysts. They utilized none of the 24 kinds of carbohydrates tested. Polysaccharides such as agar, cellulose, and chitin were not decomposed. The guanine plus cytosine proportional content in the DNA was 31.3 to 32.5%. The organisms grew in media prepared with sea water or a synthetic sea water, but did not in those with NaCl alone. On the basis of these characteristics, it was considered that the present organisms should be placed in the genus Flexibacter. The organism was found to be distinct in its various characteristics and pathogenicity to fish from any formally established species of the genus Flexibacter, and, therefore, it was classified as a new species.