My research project
Encapsulating bacteria to create functional biocoatings
Biocoatings (or biocomposites) are “living paints” made from colloidal polymers (i.e. synthetic latex) which encapsulate functional, metabolically active bacteria. These biocoatings could be used for applications that do not require bioreactors and the unwanted biomass they produce. In addition, these “artificial biofilms” could facilitate the transport of functional microorganisms. In addition to the synthetic latex, our biocoatings’ formulation features halloysite nanotubes to increase the porosity and therefore to enhance gaseous exchanges and bacterial hydration. Our studies have been carried out using E. coli as a model organism, as well as cyanobacteria, the marine strain Synechococcus sp. PCC 7002 and the freshwater strain Synechocystis sp. PCC 6803. The microstructure of the biocoatings revealed bacterial encapsulation and a surrounding network of pores. Higher proportions of viable bacteria were found within halloysite biocoatings than in less porous coatings. Viability within our biocoatings was assessed after the film formation process using resazurin reduction assays or luminescence-based assays (CellTiter-Glo), as well as confocal light scanning microscopy (CLSM). The use of synergistically acting populations, genetic modifications or other bacterial species, such as acetogenic bacteria, could result in advances in bioremediation, wastewater treatment and sustainable energy production.
A biocoating confines non-growing, metabolically-active bacteria within a synthetic colloidal polymer (i.e. latex) film. Bacteria encapsulated inside biocoatings can perform useful functions, such as a biocatalyst in wastewater treatment. A biocoating needs to have high a permeability to allow a high rate of mass transfer for rehydration and the transport of both nutrients and metabolic products. It therefore requires an interconnected porous structure. Tuning the porosity architecture is a challenge. Here, we exploited rigid tubular nanoclays (halloysite) and non-toxic latex particles (with a relatively high glass transition temperature) as the colloidal “building blocks” to tailor the porosity inside biocoatings containing Escherichia coli bacteria as a model organism. Electron microscope images revealed inefficient packing of the rigid nanotubes and proved the existence of nanovoids along the halloysite/polymer interfaces. Single-cell observations using confocal laser scanning microscopy provided evidence for metabolic activity of the E. coli within the biocoatings through the expression of yellow fluorescent protein. A custom-built apparatus was used to measure the permeability of a fluorescein sodium salt in the biocoatings. Whereas there was no measurable permeability in a coating made from only latex particles, the permeability coefficient of the composite biocoatings increased with increasing halloysite content up to a value of 110-4 m h-1. The effects of this increase in permeability was demonstrated through a specially-developed resazurin reduction assay. Bacteria encapsulated in halloysite composite biocoatings had statistically significant higher metabolic activities in comparison to bacteria encapsulated in a non-optimized coating made from latex particles alone.