Pseudoalteromonas piscicida X-8 causes bleaching disease in farmed Saccharina japonica

Saccharina japonica is a commercially farmed seaweed of global importance. However, disease occurrence during different stages cultivation can result in substantial economic losses. Identification the causative agents remains significant bottleneck to large scale S. japonica. In this study, an aerobic heterotrophic, flagellated, rod-shaped Gram-negative bacterial strain X-8 was isolated from bleaching diseased sporelings. Pathogenecity tested by re-infection assay. The ultrastructural changes infected cells indicated that chloroplasts were first organelle responding infection with deformed structure and later followed fragmented nucleus. ultra-structure mitochondria cell wall remained intact re-infection. Based on 16S rRNA gene sequence, morphological biochemical characteristics, designated as Pseudoalteromonas piscicida X-8. pathogenicity P. identified Koch's Postulate under laboratory conditions. Our results will not only help establish stable experimental model between pathogenic bacteria host further elucidate virulence mechanisms, but also provide information for management effectively prevent mitigate at nursery stage.