Phosphorus limitation induces membrane lipid remodeling in aquatic phytoplankton

Phosphorus (P) is a critical limiting nutrient for phytoplankton growth in aquatic ecosystems. Under P-limitation, phytoplankton adapt by remodeling membrane lipids, replacing phospholipids (PLs) with non-P lipids such as sulfolipid sulfoquinovosyldiacylglycerol (SQDG) and betaine lipids (BLs). This mechanism is essential for reevaluating the relationship between phosphate (PO₄^3-) concentrations and primary productivity. This review synthesizes lipid composition changes in cyanobacteria and eukaryotic phytoplankton from laboratory cultures and natural aquatic ecosystems to elucidate the mechanisms of this adaptation. Under P-limited conditions, PLs like phosphatidylglycerol (PG) decrease significantly, while SQDG increases in both cyanobacteria and eukaryotic phytoplankton. This is accompanied by a pronounced increase in the SQDG:PG ratio, indicating enhanced sulfolipid synthesis to compensate for phospholipid depletion. Differently, BLs increase exclusively in eukaryotic phytoplankton, with an obvious increase in the BL: phosphatidylcholine (PC) ratio, indicating BL substitution for PC as an additional mechanism in membrane lipid remodeling, but absent in cyanobacteria. The SQDG:PG ratio negatively correlates with dissolved P concentrations, indicating the prevalence of sulfolipid substitution under P limitation. Collectively, phytoplankton adapt through coordinated pathways involving phospholipid degradation and non-P lipid biosynthesis. Sulfolipid substitution occurs in the thylakoid membranes of phytoplankton. This substitution maintains the integrity of thylakoid membranes, thereby sustaining primary productivity and the carbon cycle in aquatic ecosystems.