Self-Assembled Nanoscale Manganese Oxides Enhance Carbon Capture by Diatoms

Continuous CO2 emissions from human activities increase atmospheric CO2 concentrations and affect global climate change. The carbon storage capacity of the ocean is 20-fold higher than that of the land, and diatoms contribute to approximately 40% of carbon capture in the ocean. Manganese (Mn) is a major driver of marine phytoplankton growth and the marine carbon pump. Here, we discovered self-assembled manganese oxides (MnOx) for CO2 fixation in a diatom-based biohybrid system. MnOx shared key features (e.g., di-μ-oxo-bridged Mn–Mn) with the Mn4CaO5 cluster of the biological catalyst in photosystem II and promoted photosynthesis and carbon capture by diatoms/MnOx. The CO2 capture capacity of diatoms/MnOx was 1.5-fold higher than that of diatoms alone. Diatoms/MnOx easily allocated carbon into proteins and lipids instead of carbohydrates. Metabolomics showed that the contents of several metabolites (e.g., lysine and inositol) were positively associated with increased CO2 capture. Diatoms/MnOx upregulated six genes encoding photosynthesis core proteins and a key rate-limiting enzyme (Rubisco, ribulose 1,5-bisphosphate carboxylase–oxygenase) in the Calvin–Benson–Bassham carbon assimilation cycle, revealing the link between MnOx and photosynthesis. These findings provide a route for offsetting anthropogenic CO2 emissions and inspiration for self-assembled biohybrid systems for carbon capture by marine phytoplankton.