Oleic-acid functionalized mesoporous silica nanoparticles with a hydroxyapatite core enhanced growth of the hydrocarbon degrader Dietzia maris at oil–water interfaces

Abstract

Rapid biodegradation of poorly water-soluble hydrocarbons as nonaqueous (oil) phases in contaminated aquatic environments is enabled by attachment of hydrocarbon-degrading bacteria to the oil–water interface. Herein, we report the synthesis of nanoparticles comprising a hydroxyapatite (Ca5(PO4)3(OH)) core encapsulated in a mesoporous silica shell and surface-modified with oleic acid (OA–nHAP@MSN) for targeted binding at the oil–water interface and to supply P to bacteria at the interface. P is an essential and often limiting nutrient for bacteria in hydrocarbon-contaminated environments. In microcosm experiments, where the hydrocarbon-degrading bacteria, Dietzia maris strain NWWC4, and OA–nHAP@MSN were inoculated in mineral media in contact with pure liquid hexadecane (sole C source), there was 419.6–fold growth at the hexadecane-water interface, compared to 31.2-fold in identical, but NP-free microcosms. The continuous release of P from the hydroxyapatite core in OA–nHAP@MSN to water was demonstrated in separate experiments in well mixed batch systems and was found to be pH-sensitive. Environmental Scanning Electron Microscopy showed significantly larger cell aggregates and dense biofilms in the OA–nHAP@MSN–amended systems, compared to NP-free systems. Our results demonstrate a strategy for enhancing oil–spill bioremediation using NPs targeting nutrient supply to hydrocarbon-degrading bacteria at oil-water interfaces.