Abstract
In this study, we usedin situtransplantations to provide the first evidence of horizontal acquisition of cyanobacterial symbionts by a marine sponge. The acquisition of the symbionts by the host spongePetrosia ficiformis, which was observed in distinct visible patches, appeared several months after transplantation and at different times on different sponge specimens. We further used 16S rRNA gene amplicon sequencing of genomic DNA (gDNA) and complementary DNA (cDNA) and metatranscriptomics to investigate how the acquisition of the symbiotic cyanobacteriumCandidatusSynechococcus feldmannii perturbed the diverse microbiota associated with the hostP.ficiformis. To our surprise, the microbiota remained relatively stable during cyanobacterial symbiont acquisition at both structural (gDNA content) and activity (cDNA expression) levels. At the transcriptomic level, photosynthesis was the primary function gained following the acquisition of cyanobacteria. Genes involved in carotene production and oxidative stress tolerance were among those highly expressed byCa. S. feldmannii, suggesting that this symbiont may protect itself and its host from damaging light radiation.