Molecular Mechanisms Underpinning Aggregation in sp. C61 Isolated from Iron-Rich Pelagic Aggregates.

Iron-rich pelagic aggregates (iron snow) are hot spots for microbial interactions. Using iron snow isolates, we previously demonstrated that the iron-oxidizer sp. C25 triggers sp. C61 aggregation by producing the infochemical 2-phenethylamine (PEA). Here, we showed slightly enhanced aggregate formation in the presence of PEA on different spp. but not other iron-snow microorganisms, including sp. C78 and sp. PN-J47. Next, we sequenced the sp. C61 genome to reconstruct its metabolic potential. Pangenome analyses of spp. genomes revealed the core genome contained 65 gene clusters associated with aggregation, including autoaggregation, motility, and biofilm formation. Screening the sp. C61 genome revealed the presence of autotransporter, flagellar, and extracellular polymeric substances (EPS) production genes. RNA-seq analyses of sp. C61 incubations (+/- 10 µM PEA) indicated genes involved in energy production, respiration, and genetic processing were the most upregulated differentially expressed genes in the presence of PEA. Additionally, genes involved in flagellar basal body synthesis were highly upregulated, whereas the expression pattern of biofilm formation-related genes was inconclusive. Our data shows aggregation is a common trait among spp. and PEA stimulates the central cellular metabolism, potentially advantageous in aggregates rapidly falling through the water column.