Contrasting microbial communities drive iron cycling across global biomes

Abstract The global iron (Fe) cycle governs important aspects of biosphere function by defining Fe availability thus supporting productivity of terrestrial and ocean ecosystems. However, the link between soil microbiome function to global patterns in terrestrial iron cycling remains poorly investigated. Here, we developed a novel database termed IRon cycle Annotation (IRcyc-A) targeted at discovering and annotating Fe cycle genes within omics data that we validated against known localized patterns of iron cycling. We leveraged this new tool to analyse the Fe cycle of over 220 publicly available soil metagenomes and metatranscriptomes encompassing a wide range of biomes on Earth. We show that the greatest abundance of Fe(III)-reduction and Fe(II)-oxidation genes were attributed to Acidobacteriota and were most abundant in the microbiomes of peatlands and iron sulfide soils, respectively. This is consistent with the high levels of dissolved Fe recorded in rivers draining such areas. In contrast, genes encoding the biosynthesis of siderophores deployed in iron sequestration in response to Fe deficiency peaked in agroecosystems with the majority assigned to Actinomycetota. Siderophore synthesis genes were negatively correlated with Fe(III)-reduction and Fe(II)-oxidation genes, supporting the view of divergent communities under low and high iron availability. Our findings highlight how iron availability shapes terrestrial microbial communities and how microbial processes can in turn contribute to global patterns in terrestrial Fe and C cycling.