Community structure of two tropical soft corals-associated bacteria

Abstract

Coral-associated bacteria have been inferred to be serving key roles in the coral holobiont, and therefore, identifying and studying the bacterial associates will provide insights into coral biology and microbial symbiosis. We investigated the bacterial community in two soft coral species (Litophyton sp. and Sinularia sp.) and surrounding seawater in the Weno island of Micronesia using 16S rDNA metabarcoding approach. In total, 18 bacterial phyla, 24 classes, 54 orders, 109 families and 222 genera were assigned in coral and seawater metagenomes. Principal Component Analysis (PCA) separated clustering of bacterial communities in three groups. In ambient seawater, Alaphaproteobacteria (58%) was pre-dominated followed by Gammaproteobacteria (22%), Cyanobacteria (13%), Bacteroidetes (4%) and others. The Litophyton sp. associated bacteria was dominated to Proteobacteria (62%) followed by Spirochates (20%), Tenericutes (6%), Bacteroidetes (2%) and others. In Sinularia sp. Spirochates (63%) was found as the major bacterial phylum and followed by Proteobacteria (20%), and unclassified bacteria (11%). Dominated Spirochaetes associated to Sinularia sp. seem to be serving the nitrogen fixation as an important holobiont. In contrast to the symbiont, the presence of Vibrio in ambient seawater implicate that the Micronesian corals can be infected by the opportunistic outbreak of these potential pathogenic bacteria due to the environmental changes caused by anthropogenic pollution and climate changes.