Newly isolated bacterium Tenacibaculum sp. strain Pbs-1 from diseased pearl oysters is associated with black-spot shell disease

Abstract In recent years, black-spot shell disease has appeared on the shells of Akoya pearl oysters, Pinctada fucata , causing serious problems in cultured pearl production. This disease was believed to be caused by boring of Polydora ciliata into calcareous substrate, and a control measure against P. ciliata was developed. As a result, boring activity of P. ciliate decreased, but black-spot shell disease remains a serious problem. We detected the genus Tenacibaculum specifically from the shells of diseased oysters using PCR-DGGE, and isolated Tenacibaculum sp. strain Pbs-1 from the diseased oyster shells. Analyses of 16S rRNA gene sequence homology and its biochemical and morphological characteristics suggested that strain Pbs-1 was a new species of Tenacibaculum . We conducted four infectivity experiments by different infection methods: smear, injection, immersion, or a combination of wound and immersion. The highest infectivity (100%) in the shell was observed in the test group by the smear method, which was accompanied by severe clinical signs that included a focal blackish discoloration of the shell. The results of the infectivity experiments indicated that the newly isolated Tenacibaculum sp. strain Pbs-1 is one of the putative causative agents of black-spot shell disease in Akoya pearl oysters.