Use of silica-encapsulated Pseudomonas sp. strain NCIB 9816-4 in biodegradation of novel hydrocarbon ring structures found in hydraulic fracturing waters.

The most problematic hydrocarbons in hydraulic fracturing (fracking) wastewaters consist of fused, isolated, bridged, and spiro ring systems, and ring systems have been poorly studied with respect to biodegradation, prompting the testing here of six major ring structural subclasses using a well-characterized bacterium and a silica encapsulation system previously shown to enhance biodegradation. The direct biological oxygenation of spiro ring compounds was demonstrated here. These and other hydrocarbon ring compounds have previously been shown to be present in flow-back waters and waters produced from hydraulic fracturing operations. Pseudomonas sp. strain NCIB 9816-4, containing naphthalene dioxygenase, was selected for its broad substrate specificity, and it was demonstrated here to oxidize fundamental ring structures that are common in shale-derived waters but not previously investigated with this or related enzymes. Pseudomonas sp. NCIB 9816-4 was tested here in the presence of a silica encasement, a protocol that has previously been shown to protect bacteria against the extremes of salinity present in fracking wastewaters. These studies demonstrate the degradation of highly hydrophobic compounds by a silica-encapsulated model bacterium, demonstrate what it may not degrade, and contribute to knowledge of the full range of hydrocarbon ring compounds that can be oxidized using Pseudomonas sp. NCIB 9816-4.

Silica-PEG gel immobilization of mammalian cells.

In this study, human foreskin fibroblasts and mouse embryonic fibroblasts were encapsulated in mechanically reversible, THEOS and THEOS-PEG gels that completely immobilized them restricting their motility, growth and proliferation. The changes in the membrane integrity and metabolic activity (MA) of the immobilized cells were measured by IR spectroscopy and fluorescence microscopy. To explore the effects of surface chemistry and porosity on immobilized cell MA, different amounts of a biocompatible polymer, polyethylene glycol PEG, was incorporated into the silica gels. To explore the effects of the proliferative stress, in selected experiments, cellular proliferation was arrested prior to immobilization by exposing the cells to irradiation. Four main factors were identified that affect the long-term survival of the cells within the immobilization matrix: (1) porosity/permeability of the gel, (2) structural homogeneity of the gel, (3) specific interactions between the cell membrane and the gel surface and (4) the proliferative stress. It was shown that the immobilized cells could easily be mechanically recovered from the gel and upon incubation, proliferated normally. It is believed that the gels and the matrix developed here have very significant potential applications in tissue engineering and in personalized cancer treatment.

Silica gel-encapsulated AtzA biocatalyst for atrazine biodegradation.

Encapsulation of recombinant Escherichia coli cells expressing a biocatalyst has the potential to produce stable, long-lasting enzyme activity that can be used for numerous applications. The current study describes the use of this technology with recombinant E. coli cells expressing the atrazine-dechlorinating enzyme AtzA in a silica/polymer porous gel. This novel recombinant enzyme-based method utilizes both adsorption and degradation to remove atrazine from water. A combination of silica nanoparticles (Ludox TM40), alkoxides, and an organic polymer was used to synthesize a porous gel. Gel curing temperatures of 23 or 45 °C were used either to maintain cell viability or to render the cells non-viable, respectively. The enzymatic activity of the encapsulated viable and non-viable cells was high and extremely stable over the time period analyzed. At room temperature, the encapsulated non-viable cells maintained a specific activity between (0.44 ± 0.06) µmol/g/min and (0.66 ± 0.12) µmol/g/min for up to 4 months, comparing well with free, viable cell-specific activities (0.61 ± 0.04 µmol/g/min). Gels cured at 45 °C had excellent structural rigidity and contained few viable cells, making these gels potentially compatible with water treatment facility applications. When encapsulated, non-viable cells were assayed at 4 °C, the activity increased threefold over free cells, potentially due to differences in lipid membranes as shown by FTIR spectroscopy and electron microscopy.