Isolation and identification of a pathogenic bacterium, Exiguobacterium oxidotolerans XP-2, from the abnormal diseased mature sporophytes of a commercially cultivated brown seaweed Saccharina japonica

Diseases of the commercially cultivated brown seaweed Saccharina japonica have been noticed since 1960s in China. However, usually opportunistic nature pathogenic bacteria seaweeds is still a main obstacle for isolating and identifying responsible causing diseases S. japonica. In this study, Gram-positive bacterium XP-2 was isolated from abnormal diseased mature sporophytes Pathogenicity test indicated that could cause green-rotten disease healthy juvenile significant algal ultrastructural changes were observed after infected by XP-2. The cells shrank, thylakoids chloroplasts became blurred 12 h re-infection. At 24 slight deformation structure mitochondria, chloroplasts, nucleus. There also many vacuoles cells. After 31 re-infection, mitochondrial more indistinct. SEM TEM observations rod-shaped with no flagella. Analysis full length 16S rRNA gene sequence physiological chemical characteristics closely related to Exiguobacterium oxidotolerans 12280 T. Based on these results, designated pathogenicity E. identified Koch’s Postulate under laboratory conditions. These results enrich growing list provide foundation investigating virulence mechanisms near future.