ABSTRACTWe propose a novel approach to continuous bioprocessing of gases. A miniaturized, coated‐paper strip, high gas fraction, biocomposite absorber has been developed using slowly shaken horizontal anaerobic tubes. Concentrated Clostridium ljungdahlii OTA1 was used as a model system. These gas absorbers demonstrate elevated CO mass transfer with low power input, reduced liquid requirements, elevated substrate consumption, and increased product secretion compared to shaken suspended cells. Concentrated OTA1 cell paste was coated by extrusion onto chromatography paper. The immobilized system shows high, constant reactivity immediately upon rehydration. Cell adhesion was by adsorption to the cellulose fibers; visualized by SEM. The C. ljungdahlii OTA1 coated paper mounted above the liquid level absorbs CO and H2 from a model syngas secreting acetate with minimal ethanol. At 100 rpm shaking speed (7.7 Wm−3) the optimal cell loading is 6.5 gDCW m−2 to maintain high CO absorbing reactivity without the cells coming off of the paper into the liquid phase. Reducing the medium volume from 10 mL to 4 mL (15% of tube volume) did not decrease CO reactivity. The reduced liquid volume increased secreted product concentration by 80%. The specific CO consumption by paper biocomposites was higher at all shaking frequencies <100 rpm than suspended cells under identical incubation conditions. At 25 rpm the biocomposite outperforms suspended cells for CO absorption by 2.5‐fold, with an estimated power reduction of 97% over the power input at 100 rpm. The estimated minimum kLa for miniaturized biocomposite gas‐absorbers is ∼100 h−1, 10 to 104 less power input than other syngas fermentation systems reported in the literature at similar kLa. Specific consumption rates in a biocomposite were ∼14 mmol h−1. This work intensified CO absorption and reactivity by 14‐fold to 94 mmol CO m−2 h−1 over previous C. ljungdahlii OTA1 work by our group. Specific acetate production rates were 23 mM h−1 or 46 mmol m−2 h−1. The specific rates and apparent kLa scaled linearly with biocomposite coating area. Biotechnol. Bioeng. 2016;113: 1913–1923. © 2016 Wiley Periodicals, Inc.

ABSTRACTAlthough 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. Biotechnol. Bioeng. 2015;112: 263–271. © 2014 Wiley Periodicals, Inc.

We formulated a latex ink for ink-jet deposition of viable Gram-negative bacterium Gluconobacter oxydans as a model adhesive, thin, highly bio-reactive microstructured microbial coating. Control of G. oxydans latex-based ink viscosity by dilution with water allowed ink-jet piezoelectric droplet deposition of 30 × 30 arrays of two or three droplets/dot microstructures on a polyester substrate. Profilometry analysis was used to study the resulting dry microstructures. Arrays of individual dots with base diameters of ~233–241 µm were obtained. Ring-shaped dots with dot edges higher than the center, 2.2 and 0.9 µm respectively, were obtained when a one-to-four diluted ink was used. With a less diluted ink (one-to-two diluted), the microstructure became more uniform with an average height of 3.0 µm, but the ink-jet printability was more difficult. Reactivity of the ink-jet deposited microstructures following drying and rehydration was studied in a non-growth medium by oxidation of 50 g/L D-sorbitol to L-sorbose, and a high dot volumetric reaction rate was measured (~435 g·L−1·h−1). These results indicate that latex ink microstructures generated by ink-jet printing may hold considerable potential for 3D fabrication of high surface-to-volume ratio biocoatings for use as microbial biosensors with the aim of coating microbes as reactive biosensors on electronic devices and circuit chips.

ABSTRACTWe 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. Biotechnol. Bioeng. 2014;111: 1993–2008. © 2014 Wiley Periodicals, Inc.

Continuous convective-sedimentation assembly (CCSA) is a deposition method that constantly supplies the coating suspension to the meniscus behind the coating knife by inline injection, allowing for steady-state deposition of ordered colloids (which may include particles or cells or live cell-particle blends) by water evaporation. The constant inflow of suspended particles available for transport to the drying front yields colloidal arrays with significantly larger surface areas than previously described and thus expands the ability of convective assembly to deposit monolayers or very thin films of multiple sizes of particles on large surfaces. Using sulfated polystyrene microspheres as a model system, this study shows how tunable process parameters, namely particle concentration, fluid sonication, and fluid density, influence coating homogeneity when the meniscus is continuously supplied. Fluid density and fluid flow-path sonication affect particle sedimentation and distribution. Coating microstructure, analyzed in terms of void space, does not vary significantly with relative humidity or suspended particle concentration. This study evaluated two configurations of the continuous convective assembly method in terms of ability to control coating microstructure by varying the number of suspended polymer particles available for transport to the coating drying front through variations in the meniscus volume.

SummaryTo assess the applicability of latex cell coatings as an ‘off‐the‐shelf’ biocatalyst, the effect of osmoprotectants, temperature, humidity and O2 on preservation of H2 production in Rhodopseudomonas palustris coatings was evaluated. Immediately following latex coating coalescence (24 h) and for up to 2 weeks of dry storage, rehydrated coatings containing different osmoprotectants displayed similar rates of H2 production. Beyond 2 weeks of storage, sorbitol‐treated coatings lost all H2 production activity, whereas considerable H2 production was still detected in sucrose‐ and trehalose‐stabilized coatings. The relative humidity level at which the coatings were stored had a significant impact on the recovery and subsequent rates of H2 production. After 4 weeks storage under air at 60% humidity, coatings produced only trace amounts of H2 (0–0.1% headspace accumulation), whereas those stored at < 5% humidity retained 27–53% of their H2 production activity after 8 weeks of storage. When stored in argon at < 5% humidity and room temperature, R. palustris coatings retained full H2 production activity for 3 months, implicating oxidative damage as a key factor limiting coating storage. Overall, the results demonstrate that biocatalytic latex coatings are an attractive cell immobilization platform for preservation of bioactivity in the dry state.

Fabricating industrial-scale photoreactive composite materials containing living cells, requires a deposition strategy that unifies colloid science and cell biology. Convective assembly can rapidly deposit suspended particles, including whole cells and waterborne latex polymer particles into thin (<10 µm thick), organized films with engineered adhesion, composition, thickness, and particle packing. These highly ordered composites can stabilize the diverse functions of photosynthetic cells for use as biophotoabsorbers, as artificial leaves for hydrogen or oxygen evolution, carbon dioxide assimilation, and add self-cleaning capabilities for releasing or digesting surface contaminants. This paper reviews the non-biological convective assembly literature, with an emphasis on how the method can be modified to deposit living cells starting from a batch process to its current state as a continuous process capable of fabricating larger multi-layer biocomposite coatings from diverse particle suspensions. Further development of this method will help solve the challenges of engineering multi-layered cellular photocomposite materials with high reactivity, stability, and robustness by clarifying how process, substrate, and particle parameters affect coating microstructure. We also describe how these methods can be used to selectively immobilize photosynthetic cells to create biomimetic leaves and compare these biocomposite coatings to other cellular encapsulation systems.

Filtration of an isotonic suspension of baker's yeast through a 0.45‐μm membrane was studied at two different pressures, 40 and 80 kPa, for yeast concentrations ranging from 0.14 to 51 kg/m 3 (dry weight). For a yeast volume fraction above 0.06 (∼21.8 kg/m 3 ), the porosity of the yeast cake is less dependent on the suspension concentration. For highly diluted suspensions, the specific cake resistance approaches a minimum that depends on the filtration pressure. Correlation functions of cake porosity and specific cake resistance were obtained for the concentration range investigated showing that the Kozeny–Carman coefficient increases when the applied pressure increases. Both filtration pressure and slurry concentration can be process controlled. In the range of moderate yeast concentration, the filtrate flux may be increased by manipulating the filtration pressure and the slurry concentration, thereby improving the overall process efficiency. The complex behavior of yeast cakes at high slurry concentration can be described by a conventional model as long as part of yeast cells are assumed to form aggregates, which behave as single bigger particles. The aggregation effect may be accounted for using a binary mixture model. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012

The structures resulting from convective-sedimentation assembly (CSA) of bimodal suspensions (4.1–10% solids) of strongly charged sulfate latex microspheres (zeta potential −55.9±1.8mV at pH 8.0) and weakly charged Saccharomyces cerevisiae (zeta potential −18.7±0.71mV at pH 8.0) on glass, polyester, polypropylene, and aluminum foil substrates was evaluated. This study shows how substrate wettability, suspension composition, particle size ratio and surface charge affect the deposition process and resulting coating microstructure (particle ordering and void space). Size ratio and charge influence deposition, convective mixing or demixing and relative particle locations. Substrate wettability and suspension composition influence coating microstructure by controlling suspension delivery and spreading across the substrate. S. cerevisiae behave like negatively-charged colloidal particles during CSA. CSA of particle–yeast blends result in open-packed structures (15–45% mean void space), instead of tightly packed coatings attainable with single component systems, confirming the existence of significant polymer particle–yeast interactions and formation of particle aggregates that disrupt coating microstructure during deposition. Further optimization of the process should allow void space reduction and deposition of cells plus adhesive polymer particles into tightly packed adhesive monolayer coatings for biosensors, biophotoabsorbers, energy applications, and highly reactive microbial absorbers.

This chapter describes a method for generating uniform lab-scale biocatalytic nanoporous latex coatings. Nearly everything we come into contact with on a daily basis has been coated with some polymer material. High-speed waterborne polymer coating and ink-jet printing techniques are mature technologies. Methods for immobilizing microorganisms in lab-scale waterborne latex biocatalytic coatings draw on existing coating technologies for generating precision industrial paint and paper coatings and would therefore be amenable to scale up in future applications. An inherent problem for many lab-scale techniques is coating uniformity. The method described here has been developed to dramatically increase the uniformity of multiple individual small surface area coatings derived from a single coating template by minimizing edge effects due to emulsion drying adjacent to the edge of the mask.

A model-based investigation of the reactivity of a multi-phase microchannel bioreactor for the oxidation of d-sorbitol to l-sorbose by viable Gluconobacter oxydans entrapped in an adhesive, bilayer, and nano-porous latex coating has been performed. Using kinetics and mass-transfer information from literature, the overall productivity of a single microchannel was determined. For liquid and gas superficial velocities typical for monoliths and channel diameters smaller than 1000 μm, volumetric l-sorbose formation rates larger than 30 g l−1 h−1 were predicted. Since the system was approximately kinetically controlled any effort to increase the coating reactivity, for example by using thinner topcoats or improving cell viability should result in a further increase of the overall reactivity. These modeling studies should provide the basis for engineering of channel geometry, biocatalytic coating nano-porosity and thickness, coating stability, optimal reactivity and multi-phase channel flow properties for future microchannel bioreactors for high intensity microbial oxidations.

Intact cells are the most stable form of nature's photosynthetic machinery. Coating‐immobilized microbes have the potential to revolutionize the design of photoabsorbers for conversion of sunlight into fuels. Multi‐layer adhesive polymer coatings could spatially combine photoreactive bacteria and algae (complementary biological irradiance spectra) creating high surface area, thin, flexible structures optimized for light trapping, and production of hydrogen (H 2 ) from water, lignin, pollutants, or waste organics. We report a model coating system which produced 2.08 ± 0.01 mmol H 2 m −2 h −1 for 4,000 h with nongrowing Rhodopseudomonas palustris , a purple nonsulfur photosynthetic bacterium. This adhesive, flexible, nanoporous Rps. palustris latex coating produced 8.24 ± 0.03 mol H 2 m −2 in an argon atmosphere when supplied with acetate and light. A simple low‐pressure hydrogen production and trapping system was tested using a 100 cm 2 coating. Rps. palustris CGA009 was combined in a bilayer coating with a carotenoid‐less mutant of Rps. palustris (CrtI − ) deficient in peripheral light harvesting (LH2) function. Cryogenic field emission gun scanning electron microscopy (cryo‐FEG‐SEM) and high‐pressure freezing were used to visualize the microstructure of hydrated coatings. A light interaction and reactivity model was evaluated to predict optimal coating thickness for light absorption using the Kubelka‐Munk theory (KMT) of reflectance and absorptance. A two‐flux model predicted light saturation thickness with good agreement to observed H 2 evolution rate. A combined materials and modeling approach could be used for guiding cellular engineering of light trapping and reactivity to enhance overall photosynthetic efficiency per meter square of sunlight incident on photocatalysts. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010