Nanoparticle-assisted structural tailoring of trehalose lipid biosynthesis by Rhodococcus erythropolis WJ-2

Achieving sustainable and cost-effective production and modulating the structure of biosurfactants is increasingly obtaining attention due to carbon neutrality and eco-safety. Nanotechnology-assisted approaches have been emerging as a promising strategy for this purpose. Here, we investigated the effect of metal oxide nanoparticles on the yield and molecular structure of trehalose lipids produced by Rhodococcus erythropolis WJ-2. Sunflower oil was identified as the optimal carbon source against other oils, yielding 12.60 g L^-1. Subsequent optimization of four key medium components (sunflower oil, ZnSO₄, (NH₄)₂SO₄, and yeast extract) using a Box-Behnken design elevated the baseline yield to 24.75 g L^-1. Interestingly, the trehalose lipid yield was further enhanced to 28.12 g L^-1 compared to the optimized medium without NPs when supplemented with 0.5 g per L Fe₂O₃ NPs (≈20 nm). Furthermore, structural diversity analyzed by FTIR and HPLC-MS showed the obvious m/z value shifts of trehalose lipids with NPs comprising longer hydrophobic fatty acid chains and more unsaturated fatty acid derivatives. In the absence of Fe₂O₃ NPs, the main m/z peaks were detected at m/z 496, 694, 877, and 1044 (relative abundances: 14.19%, 27.08%, 44.18%, 14.55%), corresponding to short-to-medium-chain fatty acid derivatives (e.g., methyl hexanoate, methyl octanoate). In contrast, the dominant peaks shifted to m/z 673, 807, 874, and 1043 (relative abundances: 22.21%, 18.39%, 47.64%, 11.76%) with Fe₂O₃ NP supplementation. These findings suggest that the unique redox properties and high surface area of Fe₂O₃ nanoparticles could enhance the yield and modulate the structures to enable the tailored biosynthesis of glycolipids by influencing key-enzyme activity and metabolic flux. This nanoparticle-assisted fermentation strategy offers a promising route for the scalable production of designer biosurfactants for diverse industrial applications.