Escherichia coli can perform at least two modes of anaerobic hydrogen metabolism and expresses at least two types of hydrogenase activity. Respiratory hydrogen oxidation is catalysed by two 'uptake' hydrogenase isoenzymes, hydrogenase -1 and -2 (Hyd-1 and -2), and fermentative hydrogen production is catalysed by Hyd-3. Harnessing and enhancing the metabolic capability of E. coli to perform anaerobic mixed-acid fermentation is therefore an attractive approach for bio-hydrogen production from sugars. In this work, the effects of genetic modification of the genes encoding the uptake hydrogenases, as well as the importance of preculture conditions, on hydrogen production and fermentation balance were examined. In suspensions of resting cells pregrown aerobically with formate, deletions in Hyd-3 abolished hydrogen production, whereas the deletion of both uptake hydrogenases improved hydrogen production by 37% over the parent strain. Under fermentative conditions, respiratory H2 uptake activity was absent in strains lacking Hyd-2. The effect of a deletion in hycA on H2 production was found to be dependent upon environmental conditions, but H2 uptake was not significantly affected by this mutation.

Biological methods of hydrogen production are preferable to chemical methods because of the possibility to use sunlight, CO 2 and organic wastes as substrates for environmentally benign conversions, under moderate conditions. By combining different microorganisms with different capabilities, the individual strengths of each may be exploited and their weaknesses overcome. Mechanisms of bio-hydrogen production are described and strategies for their integration are discussed. Dual systems can be divided broadly into wholly light-driven systems (with microalgae/cyanobacteria as the 1 st stage) and partially light-driven systems (with a dark, fermentative initial reaction). Review and evaluation of published data suggests that the latter type of system holds greater promise for industrial application. This is because the calculated land area required for a wholly light-driven dual system would be too large for either centralised (macro-) or decentralised (micro-)energy generation. The potential contribution to the hydrogen economy of partially light-driven dual systems is overviewed alongside that of other bio-fuels such as bio-methane and bio-ethanol.Redwood et al. -Dual systems for Bio-H 2 -Reviews in Environ. Sci. Bio/Technol. 8:149 http://dx

of precious metals from wastes: an answer to manufacturing of cheap nanocatalysts for fuel cells and power generation via an integrated biorefinery?. Biotechnology Letters, Springer Verlag, 2010, 32 (12) Purpose of workWe have examined the feasibility of using palladium, being recovered microbiologically from industrial processing waste, for the manufacture of a bio-fuel cell for power production. AbstractBio-manufacturing of nano-scale palladium was achieved via enzymatically-mediated deposition of Pd from solution using Desulfovibrio desulfuricans, Escherichia coli and Cupriavidus metallidurans. Dried 'Bio-Pd' materials were sintered, applied onto carbon papers and tested as anodes in a proton exchange membrane (PEM) fuel cell for power production. At a Pd(0) loading of 25% by mass the fuel cell power using Bio-Pd D. desulfuricans (positive control) and Bio-Pd E. coli (negative control) was ~140 and ~ 30 mW respectively.Bio-Pd C. metallidurans was intermediate between these with a power output of ~ 60 mW. An engineered strain of E. coli (IC007) was previously reported to give a Bio-Pd that was >3-fold more active than Bio-Pd of the parent E. coli MC4100 (i.e. a power output of > 110 mW).Using this strain, a mixed metallic catalyst was manufactured from an industrial processing waste. This 'Bio-precious metal' ('Bio-PM') gave ~68% of the power output as commercial 2 Pd(0) and ~50% of that of Bio-Pd D. desulfuricans when used as fuel cell anodic material. The results are discussed in relation to integrated bioprocessing for clean energy.

Escherichia coli strains MC4100 (parent) and a mutant strain derived from this (IC007) were evaluated for their ability to produce hydrogen and organic acids (OAs) via fermentation. Following growth, each strain was coated with Pd(0) via bioreduction of Pd(II). Dried, sintered Pd-biomaterials (‗Bio-Pd') were tested as anodes in a proton exchange membrane (PEM) fuel cell for their ability to generate electricity from hydrogen. Both strains produced hydrogen and OAs but ‗palladized' cells of strain IC007 (BioPd IC007 ) produced ~ 3-fold more power as compared to Bio-PdMC4100 (56 and 18 mW respectively). The power output using, for comparison, commercial Pd(0) powder and Bio-Pd made from Desulfovibrio desulfuricans, was ~100 mW. The implications of these findings for an integrated energy generating process are discussed.

H2 can potentially be produced in a two-stage biological process: the fermentation of glucose by Escherichia coli HD701 and the photofermentation of the residual medium by Rhodobacter sphaeroides O.U. 001. In a typical batch fermentation, E. coli consumed glucose and produced H2, organic end-products and biomass. Organic end-products and residual glucose were removed during subsequent photofermentation by R. sphaeroides, with associated growth and neutralization of pH. However, photoproduction of H2 did not occur during photofermentation of the residual liquor per se due to the presence of fixed nitrogen compounds. Nevertheless, this two-stage approach could be applied to dispose of sugar-containing industrial wastes, H2 being used for on-site power generation.

A Rhodobacter sphaeroides-supported dried, ground palladium catalyst ("Rs-Pd(0)") was compared with a Desulfovibrio desulfuricans-supported catalyst ("Dd-Pd(0)") and with unsupported palladium metal particles made by reduction under H2 ("Chem-Pd(0)"). Cell surface-located clusters of Pd(0) nanoparticles were detected on both D. desulfuricans and R. sphaeroides but the size and location of deposits differed among comparably loaded preparations. These differences may underlie the observation of different activities of Dd-Pd(0) and Rs-Pd(0) when compared with respect to their ability to promote hydrogen release from hypophosphite and to catalyze chloride release from chlorinated aromatic compounds. Dd-Pd(0) was more effective in the reductive dehalogenation of polychlorinated biphenyls (PCBs), whereas Rs-Pd(0) was more effective in the initial dehalogenation of pentachlorophenol (PCP) although the rate of chloride release from PCP was comparable with both preparations after 2 h.

The imminent use of hydrogen as an energy vector establishes the need for sustainable production technologies based on renewable resources. Starch is an abundant renewable resource suitable for bio-hydrogen generation. It was hypothesised that starch hydrolysates from a large (250 mL) hydrothermal reactor could support bioH 2 fermentation without inhibition by toxic byproducts.Starch was hydrolysed at high concentrations (40-200 g.L -1 ) in hot compressed water (HCW) with CO 2 at 30 bar in a 250 mL reactor, the largest so far for polysaccharide hydrolysis, at 180-235 °C, 15 min. Hydrolysates were detoxified with activated carbon (AC) and tested in biohydrogen fermentations. The maximum yield of glucose was 548 g.kg starch -1 carbon at 200 °C. 5-hydroxymethyl furfural, the main fermentation inhibitor, was removed by AC to support 70% more hydrogen production than the untreated hydrolysates. The potential utilization of starch hydrolysates from HCW treatment for upscaled fermentations is promising.

The environmentally prevalent polybrominated diphenyl ether (PBDE) #47 and polychlorinated biphenyls (PCBs) #28 and #118 were challenged for 24 hours with a novel biomass-supported Pd catalyst (Bio-Pd 0 ). Analysis of the products via GC-MS revealed the Bio-Pd 0 to cause the challenged compounds to undergo stepwise dehalogenation with preferential loss of the least sterically hindered halogen atom. A mass balance for PCB #28 showed that it is degraded to three dichlorobiphenyls (33.9%), two monochlorobiphenyls (12%), and biphenyl (30.7%). The remaining mass was starting material. In contrast, while PCB #118 underwent degradation to yield five tetra-and five trichlorinated biphenyls, no less chlorinated products or biphenyl were detected, and the total mass of degraded products was 0.3%. Although the Bio-Pd 0 material was developed for treatment of PCBs, a mass balance for PBDE #47 showed that the biocatalyst could prove a potentially useful method for treatment of PBDEs. Specifically, 10% of PBDE #47 was converted to identifiable lower brominated congeners, predominantly the tribrominated PBDE #17 and the dibrominated PBDE #4, 75% remained intact, while 15% of the starting mass was unaccounted for.