Characterization of bacterial community structure in two alcyonacean soft corals (Litophyton sp. and Sinularia sp.) from Chuuk, Micronesia

Abstract

Microbes in the coral holobiont play important roles in nitrogen fixation, carbon supply, antibiotic production, mucus recycling, and food supply to maintain homeostasis in corals. However, microbes can also induce coral diseases in response to environmental changes under non-optimal conditions. Therefore, studies of microbial communities are needed to understand the health statuses of corals in response to environmental changes. In this study, we performed 16S rDNA metabarcoding to investigate the bacterial communities in two healthy alcyonacean soft coral species (Sinularia sp. and Litophyton sp.) inhabiting the coast of Weno Island (Chuuk, Micronesia) and in ambient seawater. We identified 18 bacterial phyla, 24 classes, 54 orders, 109 families, and 222 genera associated with the two corals and seawater. The bacterial communities differed in the corals and seawater. The bacterial community in Sinularia sp. was dominated by the genus Spirochaeta in Spirochaetaceae (63.9% relative abundance), followed by Endozoicomonas (10%). In Litophyton sp., the bacterial community also contained Spirochaeta (19.5%) and Endozoicomonas (4.7%), although Cellvibrionaceae (23.7%) was dominant and other groups such as Rhizobiales (11.5%) and Rhodospirillales (8.7%) were evenly distributed. In ambient seawater, the predominant bacteria were Pelagibacter (29.2%), Rhodobacteraceae (15.5%), Prochlorococcus (11.3%), and Vibrio (5.8%), which are distinct from the species in the two coral species. The microbial communities between the two alcyonacean soft corals and seawater were different, and the microbial community differences were coral species-specific.