Black Band disease-related (BBD) cyanobacterium from Okinawan corals

The number of reports of coral disease is increasing worldwide. Among coral diseases, BBD was discovered first, along Caribbean coastlines in 1973. The main symptom of BBD is a black mat on the surface of the infected coral tissue. This black mat is a microbial consortium in which a dominant filamentous cyanobacterium proliferates. In Okinawa various reports and ecological studies of BBD have been conducted, but the species of cyanobacteria associated with Okinawan BBD remain unclear. This study focused primarily on the classification of BBD cyanobacteria in Okinawa Prefecture (Sesoko-jima and Miyako-jima Islands). BBD was sampled in a colony of Montipora sp. from Sesoko-jima Island on June 15, 2015, July and August 2016, and May 2017. Two BBD tissues were sampled from colonies of Goniopora sp. at two localities of Miyako-jima Island on August 27 and 28, 2015. All samples were non-branching filamentous, with a dark brown crude culture color and round cells with a tapered tip; the Miyako-jima samples were 2.6–3.8 μm long and 3.3–4.5 μm wide, while the Sesoko-jima samples were 2.6–4.6 μm long and 3.1–4.8 μm wide. We attempted to isolate these cyanobacteria but had difficulty establishing well-growing cultures. Instead of culturing, single-filament PCR was employed to obtain partial 16S rRNA gene sequences using cyanobacteria-specific primers. Although slight morphological differences were found among samples, the 1219-bp partial 16S rRNA gene sequences obtained were identical. These sequences matched those of Roseofilum reptotaenium FJ210722. Our data suggest that the dominant cyanobacteria in different localities and different coral colonies belong to the same species, R. reptotaenium.