Underexplored rare bacterial biosphere associated with corals of the northeastern Tropical Eastern Pacific

Microbes of low abundance (i.e., rare biosphere) are involved in the ability of the coral as holobiont, to respond and acclimatize to local and global environmental disturbances. However, no complete characterization of these important microbial assemblages has been conducted. Outlining these assemblages would greatly benefit our understanding of their ecological role in the coral-microbial association. Here, we assessed the rare bacterial biosphere of the hermatypic corals Pocillopora cf. damicornis and P. cf. verrucosa, as well as the surrounding seawater and sediment, at six sites in the northeastern Tropical Eastern Pacific, using MiSeq Illumina sequencing of the 16S rRNA gene region V4. The rare biosphere presented spatial differences among sites with different anthropogenic stress levels. The four biotopes presented a similar rare microbiota. However, in sites with high anthropogenic stress, a high abundance of the Vibrionaceae family was recorded, while locations with low and moderate anthropogenic stress showed several high sequences related to the Flavobacteriaceae and Bacillaceae families. This study represents the first approach to the knowledge of the rare bacterial biosphere in P. cf. damicornis and P. cf. verrucosa in the northeast of the Eastern Tropical Pacific and its possible use as a bioindicator of the stress response to the magnitude of anthropogenic stress.