Insights into the cultured bacterial fraction of corals

Bacteria associated with coral hosts are diverse and abundant, withrecent studies suggesting involvement of these symbionts in host resilience toanthropogenic stress. Despite their putative importance, the work dedicated to cultur-ing coral-associated bacteria has received little attention. Combining published andunpublished data, here we report a comprehensive overview of the diversity and func-tion of culturable bacteria isolated from corals originating from tropical, temperate, andcold-wa ter habitats . A total of 3,055 isolat es from 52 studies were considered by ourmetasurvey. Of these, 1,045 had full-length 16S rRNA gene sequences, spanning 138 for-mally descri bed and 12 putativel y novel bacter ial gener a across the Proteobacteria,Firmicutes, Bacteroidetes,andActinobacteria phyla. We perfor me d compara ti ve genomi canalysis using the available genomes of 74 strains and identied potential signatures ofbenecial bacterium-coral symbioses among the strains. Our analysis revealed .400 bio-synthetic gene clusters that underlie the biosynthesis of antioxidant, antimicrobial, cyto-toxic, and other secondary metabolites. Moreover, we uncovered genomic features—notpreviously described for coral-bacterium symbioses—potentially involved in host coloni-zation and host-symbiont recognition, antiviral defense mechanisms, and/or integratedmetabolic interactions, which we suggest as novel targets for the screening of coralprobiotics. Our results highlight the importance of bacterial cultures to elu cidatecoral holob iont functioning and guide the selection of probiotic candidates to promote coral resilience and improve holistic and customized reef restoration and rehabilitation efforts.