Coral black band disease (BBD) is an important coral disease that has become more prevalent in recent decades due to the weakening of corals caused by warming seawaters, resulting in more coral deaths. BBD is a polymicrobial disease, which means that it is not caused by a single pathogen but multiple microbial species. BBD is caused by the formation of a biofilm of multiple microorganisms, in which these microorganisms are located in different specific layers and cooperate with each other to invade, infect, and eventually kill the coral. Because the biofilm is black in color, it is named black band disease (Figure 1, Panel A). Many studies have found that the rate of migration (and hence virulence) of BBD varies, but the factors responsible for the difference in rate of migration are unknown. A collaborative team comprised by Dr. Sen-Lin Tang at Biodiversity Research Center, Academia Sinica, and Dr. Naohisa Wada and Dr. Nobuhiro Mano at Nihon University, Japan, revealed the relationship between microbial composition and localization on the difference in migration rate was carefully analyzed, and it was found that high relative abundance of sulfur-oxidizing bacteria (Arcobacteraceae) were frequently found in the middle layer of the fast-spreading BBD, while the slow-spreading BBD was mainly composed of another group of sulfur-oxidizing bacteria (Rhodobacteraceae) (Figure 1, Panel B). This shows that the differences in microbial composition and location are closely related to the migration rate of BBD. This study is the first in the world to reveal that the microbial composition in BBD as an important determinant of virulence. And which provides a deeper understanding of coral pathogenesis. The results of the study were published in the prestigious journal: NPJ Biofilms and Microbiomes.