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

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 (HCa5O13P3) 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 31.2-fold to those 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. Petroleum liquids are hazardous contaminants and their spills have devastating ecological impacts. Biostimulation is essential for efficient oil spill bioremediation, however, addition of excessive soluble nutrients or oleophilic fertilizers as biostimulants can exacerbate ecotoxicity. To selectively biostimulate hydrocarbon degraders at the oil-water interface and as better substitutes for problematic biostimulants, we developed oleic acid-functionalized mesoporous silica nanoparticles designed to attach to oil-water interfaces and provide controlled release of P locally from encapsulated hydroxyapatite. We demonstrated that these nanoparticles drive rapid growth of a typical hydrocarbon degrader, Dietzia maris, at the oil-water interface, thus enabling efficient bioremediation without problematic biostimulants. [Display omitted] •HAP NPs in OA-coated porous silica synthesized to attach at oil-water interfaces.•NPs released phosphate at the interface which aided interfacial bacterial growth.•Up to 13 × higher D. maris growth with HAP con