Oscar I. Bernal and Michael C. Flickinger
Whole living photosynthetic cells have significant stability advantages over isolated chloroplasts, photosynthetic proteins and artificial photocatalysts for engineering photoreactive composite materials. Cells have all the necessary molecular machinery to carry out photosynthesis in a stable chemical environment and produce useful metabolites capable of generating more energy. Microbial latex paper coatings have the potential to stabilize photosynthetic reactivity by providing a porous support that keeps the cells hydrated and acts as a transport network that nourishes the cells, eliminates waste material and separates products. Here we report a novel extension of engineering cellular composite materials in which we make use of a paper matrix for long-term stabilization of photoreactive microbial biomass as an integral part of the bio-composite microstructure. This reactive microbial paper is dried prior to rehydration and shows sustained long-term reactivity following rehydration. Hydrogen gas production derived from acetate by the activity of nitrogenase in CGA009 Rps. palustris entrapped in microbial paper can be sustained >1000 hours at a rate of 4.00 ± 0.28, mmol H2 m-2 hr-1following rehydration. SEM images of composite microstructure reveal the distribution of the bacterial cells in the paper matrix as clusters between paper fibers (in their characteristic rosette morphology) that do not clog the pore space, which allows for perfusive flow through the cellulose fiber matrix. Composite microbial paper provides a beneficial microenvironment for cells to remain viable and reactive for long periods of time after drying and rehydration. This bio-composite materials approach may be promising as an inexpensive photoreactive material for solar energy trapping as a component of a microbial photo fuel cell (MPFC), for advanced biofilters and separation devices and for the production of liquid biofuel precursors where a very high concentration of cellular biomass is maintained metabolically active in a non-growth state for 1,000s of hours. Current efforts are focused on the confirmation of the non-growth state of the cells in the paper, prevention of cell leaching to the liquid phase and adaptation of the paper formation method for immobilization of a high volume fraction of viable cyanobacteria cells for CO2 recycling and O2 production.
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