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.

Two genes (mcrA and mcrB) from Streptomyces lavendulae that together confer resistance to mitomycin C were identified. This DNA appears to comprise a polycistronic operon with a drug-inducible leaderless mRNA. The deduced amino acid sequence of mcrA shows similarity to sequences of a special class of bacterial, plant, and animal oxygen oxidoreductases.

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 .

Adhesive biocatalytic coatings (biocoatings) have a nanoporous microstructure generated by partially coalesced waterborne polymer particles that entrap highly concentrated living cells in a dry state stabilized by carbohydrate osmo-protectants. Biocoatings can be deposited by high speed coating technologies, aerosol delivery or ink-jet printed in multilayered, patterned coatings on flexible nonporous or nonwoven substrates, preserving 10 10-10 12 non-growing viable microorganisms per m 2 in 2-50 m thick layers. Cells are rehydrated to restore their metabolism. The layers reactive half-life following rehydration can be 1000 s of hours. The planar structure of biocoatings enable uniform illumination of a high concentration of photo-reactive microorganisms or algae and contact these microbe with thin liquid films for efficient mass transfer. This review highlights recent advances in biocoating technology for pollutants degradation, photo-reactive coatings, stabilization of hyperthermophiles for biocatalysis, environmental biosensors, and biocomposite fuel cells. Engineering cells for desiccation tolerance, unveiling the metabolism of nongrowing cells, and engineering the interaction between the cell surface and adhesive polymer binders are fundamental challenges to open the door to vast future applications of biocoatings for environmental sensing and remediation.

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Thermostable polymers cast as thin, porous coatings or membranes may be useful for concentrating and stabilizing hyperthermophilic microorganisms as biocatalysts. Hydrogel matrices can be unstable above 65 degrees C. Therefore a 55-microm thick, two layer (cell coat + polymer top coat) bimodal, adhesive latex coating of partially coalesced polystyrene particles was investigated at 80 degrees C using Thermotoga maritima as a model hyperthermophile. Coating permeability (pore structure) was critical for maintaining T. maritima viability. The permeability of bimodal coatings generated from 0.8 v/v of a suspension of non-film-forming 800 nm polystyrene particles with high glass transition temperature (T(g) = 94 degrees C, 26.9% total solids) blended with 0.2 v/v of a suspension of film-forming 158 nm polyacrylate/styrene particles (T(g) approximately -5 degrees C, 40.9% total solids) with 0.3 g sucrose/g latex was measured in a KNO3 diffusion cell. Diffusivity ratio remained above 0.04 (D(eff)/D) when incubated at 80 degrees C in artificial seawater (ASW) for 5 days. KNO3 permeability was corroborated by cryogenic-SEM images of the pore structure. In contrast, the permeability of a mono-dispersed acrylate/vinyl acetate latex Rovace SF091 (T(g) approximately 10 degrees C) rapidly decreased and became impermeable after 2 days incubation in ASW at 80 degrees C. Thermotoga maritima were entrapped in these coatings at a cell density of 49 g cell wet weight/liter of coating volume, 25-fold higher than the density in liquid culture. Viable T. maritima were released from single-layer coatings at 80 degrees C but accurate measurement of the percentage of viable entrapped cells by plate counting was not successful. Metabolic activity could be measured in bilayer coatings by utilization of glucose and maltose, which was identical for latex-entrapped and suspended cells. Starch was hydrolyzed for 200 h by latex-entrapped cells due to the slow diffusion of starch through the polymer top coat compared to only 24 h by suspended T. maritima. The observed reactivity and stability of these coatings was surprising since cryo-SEM images suggested that the smaller low T(g) polyacrylate/styrene particles preferentially bound to the T. maritima toga-sheath during coat formation. This model system may be useful for concentrating, entrapment and stabilization of metabolically active hyperthermophiles at 80 degrees C.

Using a continuous culture of Bacillus methanolicus MGA3 limited by 100 mM methanol in the feed and growing at a dilution rate Dl025 h N1 , transients in dissolved methanol were studied to determine the effects of methanol toxicity and the pathway of methanol dissimilation to CO 2 . Steady-state cultures were disturbed by pulses of methanol resulting in a rapid change in concentration of 64-128 mM. B. methanolicus MGA3 responded to a sudden increase in available methanol by a transient decline in the biomass concentration in the reactor. In most cases the culture returned to steady state between 4 and 12 h after pulse addition. However, at a methanol pulse of 128 mM, complete biomass washout occurred and the culture did not return to steady state. Integrating the response curves of the dry biomass concentration over a 12 h time period showed that a methanol pulse can cause an average transient decline in the biomass yield of up to 22 %. 13 C NMR experiments using labelled methanol indicated that the transient partial or complete biomass washout was probably caused by toxic accumulation of formaldehyde in the culture. These experiments also showed accumulation of formate, indicating that B. methanolicus possesses formaldehyde dehydrogenase and formate dehydrogenase activity resulting in a methanol dissimilation pathway via formate to CO 2 . Studies using isotope-ratio mass spectrometry provided further evidence of a methanol dissimilation pathway via formate. B. methanolicus MGA3, growing continuously under methanol limitation, consumed added formate at a rate of approximately 085 mmol l N1 h N1 . Furthermore, significant accumulation of 13 CO 2 in the reactor exhaust gas was measured in response to a pulse addition of [ 13 C]formic acid to the bioreactor. This indicates that B. methanolicus dissimilates methanol carbon to CO 2 in order to detoxify formaldehyde by both a linear pathway to formate and a cyclic mechanism as part of the RuMP pathway.

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