Response characteristics of bacterial communities in multiple coral genera at the early stages of coral bleaching during El Niño

Abstract

Although coral bleaching caused by high temperatures has attracted great concern, the response of the coral microbiome to bleaching has not been thoroughly explored. In this study, bacterial communities from 26 genera of semi-bleached coral in the South China Sea were studied using high-throughput sequencing during El Niño. Principal coordinates analysis (PCoA) indicated that the effect of early bleaching exceeded the effect of coral species on the bacterial communities. Bleaching caused significant changes in coral bacterial communities. Burkholderiales, Caulobacterales, Pseudomonadales, Cytophagales, Oceanospirillales, and Rhodobacterales, were significantly enriched in bleaching coral, whereas Rhizobiales, Cyanobacteria, Microtrichales, Thermoanaerobaculales, Lachnospirales, Rickettsiales, and Lactobacillales, decreased in abundance. Core bacterial OTUs (operational taxonomic units) showed that high temperatures facilitated potentially pathogenic bacteria, such as Alcaligenes, Escherichia, Acinetobacter, Staphylococcus, and Enterobacteriaceae to occupy core positions. Further bleaching resulted in a significant reduction of potential core probiotics in corals. This could increase the risk of corals contracting diseases and reduce their environmental adaptability. Network analysis indicated that the bacterial interactions in bleaching coral were more complex than unbleached coral. Bacteroidales, Burkholderiales, Caulobacterales, Lactobacillales and Rhizobiales were the main taxa that interacted with other bacteria in bleaching and unbleached corals. The presence of these dominant taxa resulted in an increase in chemoheterotrophy, hydrocarbon degradation, nitrogen respiration, and denitrification, which led to great changes in the coral microenvironment. This study comprehensively revealed the response mechanism of coral bacteria during the bleaching process.