Phycosphere bacterial communities mediate arsenic accumulation and speciation in coastal macroalgae: Evidence from...

Macroalgae are known to efficiently accumulate arsenic, however, the role of their phycosphere bacterial communities in modulating arsenic uptake and transformation remains poorly understood. This study investigates the impact of phycosphere bacterial communities on arsenic accumulation and speciation in three coastal macroalgae species: Laminaria japonica (brown alga), Ulva pertusa Kjellman (green alga), and Mazzaella japonica (red alga). Among the three, L. japonica exhibited higher total arsenic content than M. japonica and U. pertusa. Phycosphere bacterial communities differed significantly among the macroalgae species in both α- and β-diversity and were strongly correlated with variations in intracellular arsenic species. Functional gene predictions indicated enrichment of pst and GST genes in L. japonica and M. japonica, associated with enhanced arsenic uptake and detoxification, while arsC was more abundant in the U. pertusa phycosphere, suggesting a preference for arsenate reduction pathways. These findings reveal the distinct roles of phycosphere bacterial communities among different macroalgae and their influence on the conversion of inorganic to organic arsenic, providing new insights into arsenic biogeochemistry in marine macroalgae-bacteria symbiotic systems.