Clay (aluminosilicate)-based microstructures, including halloysite clay tubes and kaolinite clay sheets, adsorb to the crude oil-water interface and form Pickering emulsions. The energy required for emulsion formation is equivalent to that provided by ocean turbulence, and the stability of the resulting droplets extends for more than a week. The increased surface area of these droplets enhances crude oil bioavailability for ubiquitous marine bacteria and makes these dispersants an environmentally friendly alternative to chemical dispersants. In this study we used Alcanivorax borkumensis and Cycloclasticus pugetii, Gram negative species that bloom in the presence of crude oil, to study growth, electron transport and biofilm production in the presence of clay microstructures. Both pristine and surface-modified clay microstructures stimulated the growth of A. borkumensis in synthetic medium containing hexadecane or crude oil as the sole carbon source. These microstructures also increased the production of the biosurfactants that aid biodegradation. Carbonized kaolinite sheets were most effective at stimulating biofilm production after 3 and 6 days of culture. Mixed cultures containing both A. borkumensis and C. pugetii appeared to produce more biofilm after 3 days than either organism alone. Confocal microscopy was used to observe cells stained with DAPI in an exopolymer matrix visualized with fluorescently labeled concanavalin A or wheat germ agglutinin. We used an OLIS CLARiTY spectrophotometer to study electron transport in the turbid solutions of intact cells plus or minus clay-based microstructures . When A. borkumensis was mixed with a carbon source under physiological solution conditions, a difference spectrum developed after 8-10 minutes. The reduced minus oxidized difference spectrum exhibited absorbance maxima at 423, 524, and 555 nm, spectral properties characteristic of redox-active b-type cytochromes. The oxidation of this cytochrome b behaves as though it is the rate-limited step during aerobic respiration of A. borkumensis on sodium pyruvate.

Clay-based microstructures as alternatives to chemical dispersants in bioremediation of crude oil: Studies with model marine organisms

255th National Meeting (2018)

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