High-resolution spatial and genomic characterization of coral-associated microbial aggregates in the coral .

Bacteria commonly form aggregates in a range of coral species [termed coral-associated microbial aggregates (CAMAs)], although these structures remain poorly characterized despite extensive efforts studying the coral microbiome. Here, we comprehensively characterize CAMAs associated with and quantify their cell abundance. Our analysis reveals that multiple phylotypes coexist inside a single CAMA. Nanoscale secondary ion mass spectrometry imaging revealed that the cells were enriched with phosphorus, with the elemental compositions of CAMAs different from coral tissues and endosymbiotic Symbiodiniaceae, highlighting a role in sequestering and cycling phosphate between coral holobiont partners. Consensus metagenome-assembled genomes of the two dominant phylotypes confirmed their metabolic potential for polyphosphate accumulation along with genomic signatures including type VI secretion systems allowing host association. Our findings provide unprecedented insights into -dominated CAMAs and the first direct physiological and genomic linked evidence of their biological role in the coral holobiont.