Bartholomew, S. N. | bioRxiv Science

bioRxiv2026

Graphene Quantum Dots Mitigate Oxidative Stress in Bacteria

Manufacturing and storage processes can expose microbes to oxidative stress, reducing viability and limiting their use in biotechnological applications. Here, we evaluate graphene quantum dots (GQDs) containing hydroxyl and carboxyl groups as protective additives that mitigate peroxide-induced oxidative stress in Escherichia coli. GQDs did not adversely affect bacterial growth under basal conditions and restored growth in the presence of hydrogen peroxide. Using the membrane-partitioning fluorescent probe C11-BODIPY, we found that GQDs reduced peroxide-induced oxidation in bacterial membranes. We further used redox-sensitive roGFP2 probes to monitor intracellular oxidative stress and found that GQDs suppressed intracellular hydrogen peroxide accumulation and attenuated disruption of glutathione redox homeostasis. Together, these results show that GQDs protect bacteria by limiting peroxide-driven oxidative damage at both membrane and intracellular levels. This work supports the potential use of GQDs as protective additives for microbial formulations that are susceptible to oxidative stress.

microbiology↗

bioRxiv2025

Membrane curvature enhances lipid peroxidation in a composition-dependent manner

Excessive production of reactive oxygen species (ROS) in cells results in oxidative stress, which can promote lipid oxidation in cellular membranes. This oxidation of membrane lipids accompanies various diseases and can even result in cell death through processes such as ferroptosis. The complex compositions and diverse morphologies of cellular membranes make understanding the mechanisms of lipid oxidation challenging, especially when attempting to investigate membrane composition and curvature simultaneously. Here, we utilize reconstituted lipid membranes and the fluorescent oxidation probe C11-BODIPY to quantify oxidation in lipid bilayers as functions of both lipid composition and membrane curvature. By tethering synthetic lipid vesicles to glass substrates, we were able to monitor oxidation of the fluorescent probe on a per vesicle basis using fluorescence microscopy. Our results demonstrate that highly curved membranes markedly increase both the rate and extent of oxidation across diverse membrane compositions. This effect arises from greater exposure of lipid tails to the aqueous environment, which allows more efficient transport of ROS into the hydrophobic core of the bilayer. Compositional effects on oxidation are most pronounced in membranes with low curvature (i.e., greater than 100 nm diameter) and become progressively weaker as curvature increases. We found that low to moderate cholesterol levels (i.e., 10-25 mol%) suppress curvature-dependent oxidation by tightening lipid packing, whereas high cholesterol content (i.e., 50 mol%) restores curvature sensitivity by influencing lateral lipid mobility. Together, these findings establish membrane curvature and lipid composition as interdependent determinants of oxidative susceptibility, offering new insight into how cells regulate or resist oxidative stress. Statement of significanceOxidative stress drives lipid oxidation in cellular membranes, but the combined influence of membrane curvature and composition remains poorly defined. Using reconstituted lipid vesicles and a fluorescent oxidation probe, we show that oxidation in lipid bilayers is enhanced in smaller vesicles (i.e., highly curved membranes). The oxidation rate increases with unsaturated lipids, while cholesterol suppresses this effect. Measurements of membrane packing and diffusivity support these findings, demonstrating how curvature and composition together govern membrane susceptibility to oxidative damage. These results provide new insight into the physicochemical basis of membrane stability under oxidative stress and have broad implications for understanding the vulnerability of curved cellular membranes.

biophysics↗