Fabrication of Photoreactive Biocomposite Coatings via Electric Field-Assisted Assembly of Cyanobacteria.

We report how dielectrophoresis (DEP) can be used as a tool for the fabrication of biocomposite coatings of photoreactive cyanobacteria (Synechococcus PCC7002) on flexible polyester sheets (PEs). The PE substrates were precoated by a layer-by-layer assembled film of charged polyelectrolytes. In excellent agreement between experimental data and numerical simulations, the directed assembly process driven by external electric field results in the formation of 1D chains and 2D sheets by the cells. The preassembled cyanobacteria chains and arrays became deposited on the substrate and remained in place after the electric field was turned off due to the electrostatic attraction between the negatively charged cell surfaces and the positively charged polyelectrolyte-coated PE. The DEP-assisted packing of cyanobacteria is close to the maximal surface coverage of ∼70% estimated from convectively assembled monolayers. Confocal laser scanning microscopy and spectrophotometry confirm that the photosynthetic pigment integrity of the Synechococcus cells is preserved after DEP immobilization. The significant decrease of the light scattering and the enhanced transmittance of these field-assembled cyanobacteria coatings demonstrate reduced self-shading compared to suspension cultures. Thus, we achieved the assembly of structured cyanobacteria coatings that optimize cell surface coverage and preserve cell viability after immobilization. This is a step toward the development of flexible multilayered cell-based photoabsorbing biomaterials that can serve as components of "biomimetic leaves" for utilizing solar energy to recycle CO2 into fuels or chemicals.

Biocatalytic coatings for air pollution control: a proof of concept study on VOC biodegradation.

Although biofilm-based biotechnologies exhibit a large potential as solutions for off-gas treatment, the high water content of biofilms often causes pollutant mass transfer limitations, which ultimately limit their widespread application. The present study reports on the proof of concept of the applicability of bioactive latex coatings for air pollution control. Toluene vapors served as a model volatile organic compound (VOC). The results showed that Pseudomonas putida F1 cells could be successfully entrapped in nanoporous latex coatings while preserving their toluene degradation activity. Bioactive latex coatings exhibited toluene specific biodegradation rates 10 times higher than agarose-based biofilms, because the thin coatings were less subject to diffusional mass transfer limitations. Drying and pollutant starvation were identified as key factors inducing a gradual deterioration of the biodegradation capacity in these innovative coatings. This study constitutes the first application of bioactive latex coatings for VOC abatement. These coatings could become promising means for air pollution control.

Specific photosynthetic rate enhancement by cyanobacteria coated onto paper enables engineering of highly reactive cellular biocomposite "leaves".

We describe a latex wet coalescence extrusive coating method that produces up to 10-fold specific photosynthetic rate enhancements by nitrate-limited non-growing cyanobacteria deposited onto paper, hydrated and placed in the gas-phase of small tube photobioreactors. These plant leaf-like biocomposites were used to study the tolerance of cyanobacteria strains to illumination and temperature using a solar simulator. We report sustained CO2 absorption and O2 production for 500 h by hydrated gas-phase paper coatings of non-growing Synechococcus PCC7002, Synechocystis PCC6803, Synechocystis PCC6308, and Anabaena PCC7120. Nitrate-starved cyanobacteria immobilized on the paper surface by the latex binder did not grow out of the coatings into the bulk liquid. The average CO2 consumption rate in Synechococcus coatings is 5.67 mmol m(-2) h(-1) which is remarkably close to the rate reported in the literature for Arabidopsis thaliana leaves under similar experimental conditions (18 mmol m(-2) h(-1) ). We observed average ratios of oxygen production to carbon dioxide consumption (photosynthetic quotient, PQ) between 1.3 and 1.4, which may indicate a strong dependence on nitrate assimilation during growth and was used to develop a non-growth media formulation for intrinsic kinetics studies. Photosynthetic intensification factors (PIF) (O2 production by nitrate-limited cyanobacteria in latex coatings/O2 produced by nitrate-limited cell suspensions) in cyanobacteria biocomposites prepared from wet cell pellets concentrated 100- to 300-fold show 7-10 times higher specific reactivity compared to cells in suspension under identical nitrate-limited non-growth conditions. This is the first report of changes of cyanobacteria tolerance to temperature and light intensities after deposition as a thin coating on a porous matrix, which has important implications for gas-phase photobioreactor design using porous composite materials. Cryo-fracture SEM and confocal microscopy images of cell coating distribution on the paper biocomposite suggest that the spatial arrangement of the cells in the coating can affect photoreactivity. This technique could be used to fabricate very stable, multi-organism composite coatings on flexible microfluidic devices in the gas-phase capable of harvesting light in a broader range of wavelengths, to optimize thermotolerant, desiccation tolerant, or halotolerant cyanobacteria that produce O2 with secretion of liquid-fuel precursors synthesized from CO2 .

A versatile method for preparation of hydrated microbial-latex biocatalytic coatings for gas absorption and gas evolution.

We describe a latex wet coalescence method for gas-phase immobilization of microorganisms on paper which does not require drying for adhesion. This method reduces drying stresses to the microbes. It is applicable for microorganisms that do not tolerate desiccation stress during latex drying even in the presence of carbohydrates. Small surface area, 10-65 µm thick coatings were generated on chromatography paper strips and placed in the head-space of vertical sealed tubes containing liquid to hydrate the paper. These gas-phase microbial coatings hydrated by liquid in the paper pore space demonstrated absorption or evolution of H2, CO, CO2 or O2. The microbial products produced, ethanol and acetate, diffuse into the hydrated paper pores and accumulate in the liquid at the bottom of the tube. The paper provides hydration to the back side of the coating and also separates the biocatalyst from the products. Coating reactivity was demonstrated for Chlamydomonas reinhardtii CC124, which consumed CO2 and produced 10.2 ± 0.2 mmol O2 m⁻² h⁻¹, Rhodopseudomonas palustris CGA009, which consumed acetate and produced 0.47 ± 0.04 mmol H2 m⁻² h⁻¹, Clostridium ljungdahlii OTA1, which consumed 6 mmol CO m⁻² h⁻¹, and Synechococcus sp. PCC7002, which consumed CO2 and produced 5.00 ± 0.25 mmol O2 m⁻² h⁻¹. Coating thickness and microstructure were related to microbe size as determined by digital micrometry, profilometry, and confocal microscopy. The immobilization of different microorganisms in thin adhesive films in the gas phase demonstrates the utility of this method for evaluating genetically optimized microorganisms for gas absorption and gas evolution.