Inositol phosphates as an overlooked phosphorous source in marine ecosystems

Inositol phosphates, common phosphorus storage compounds that are also crucial for eukaryotic cell signaling, constitute a significant portion of dissolved organic phosphorus in coastal waters. The hydrolysis of inositol phosphates could be an important contributor to phosphorus cycling in phosphorus-limited marine ecosystems, yet this process remains poorly understood in marine contexts. In this study, we reveal substantial concentrations of inositol phosphates in marine macrophytes, including green, brown, and red algae as well as common seagrasses, suggesting that these organisms are likely major biological sources of inositol phosphates in the oceans. A comprehensive analysis of genes involved in inositol phosphates hydrolysis in global marine metagenomes and metatranscriptomes identified key roles for γ-, α-, and δ-proteobacteria, with additional contributions from Flavobacteriia. The degradation of marine inositol phosphates was predominantly mediated by alkaline β-propeller phytases, though genes associated with acidic cysteine phytases and purple acid phytases were also widely present. Community structure and functional traits linked to inositol phosphates degradation were shaped largely by stochastic processes. Further examination of enzyme activity at the protein and community levels indicated that phytate metabolism by marine microbes is likely a widespread phenomenon in the ocean. Overall, this study highlights inositol phosphates hydrolysis as an essential yet overlooked adaptation by marine microorganisms to address phosphorus limitations in ocean ecosystems.