Strain and bioprocess improvement of a thermophilic anaerobe for the production of ethanol from wood.

Background: The thermophilic, anaerobic bacterium Thermoanaerobacterium saccharolyticum digests hemicellulose and utilizes the major sugars present in biomass. It was previously engineered to produce ethanol at yields equivalent to yeast. While saccharolytic anaerobes have been long studied as potential biomass-fermenting organisms, development efforts for commercial ethanol production have not been reported.

Increasing anaerobic acetate consumption and ethanol yields in Saccharomyces cerevisiae with NADPH-specific alcohol dehydrogenase.

Saccharomyces cerevisiae has recently been engineered to use acetate, a primary inhibitor in lignocellulosic hydrolysates, as a cosubstrate during anaerobic ethanolic fermentation. However, the original metabolic pathway devised to convert acetate to ethanol uses NADH-specific acetylating acetaldehyde dehydrogenase and alcohol dehydrogenase and quickly becomes constrained by limited NADH availability, even when glycerol formation is abolished. We present alcohol dehydrogenase as a novel target for anaerobic redox engineering of S.

Genome-scale resources for Thermoanaerobacterium saccharolyticum.

Background: Thermoanaerobacterium saccharolyticum is a hemicellulose-degrading thermophilic anaerobe that was previously engineered to produce ethanol at high yield. A major project was undertaken to develop this organism into an industrial biocatalyst, but the lack of genome information and resources were recognized early on as a key limitation.

Results: Here we present a set of genome-scale resources to enable the systems level investigation and development of this potentially important industrial organism.

Urease expression in a Thermoanaerobacterium saccharolyticum ethanologen allows high titer ethanol production.

Genes encoding the enzyme urease were integrated in a Thermoanaerobacterium saccharolyticum ethanologen. The engineered strain hydrolyzed urea, as evidenced by increased cellular growth and elevated final pH in urea minimal medium and urease activity in cell free extracts. Interestingly, replacement of ammonium salts with urea resulted in production of 54 g/L ethanol, one of the highest titers reported for Thermoanaerobacterium.

Tunable metallic-like conductivity in microbial nanowire networks.

Electronic nanostructures made from natural amino acids are attractive because of their relatively low cost, facile processing and absence of toxicity. However, most materials derived from natural amino acids are electronically insulating. Here, we report metallic-like conductivity in films of the bacterium Geobacter sulfurreducens and also in pilin nanofilaments (known as microbial nanowires) extracted from these bacteria.

Marker removal system for Thermoanaerobacterium saccharolyticum and development of a markerless ethanologen.

Marker removal strategies were developed for Thermoanaerobacterium saccharolyticum to select against the pyrF gene and the pta and ack genes. The pta- and ack-based haloacetate selective strategy was subsequently used to create strain M0355, a markerless Δldh Δpta Δack strain that produces ethanol at a high yield.

Anode biofilm transcriptomics reveals outer surface components essential for high density current production in Geobacter sulfurreducens fuel cells.

The mechanisms by which Geobacter sulfurreducens transfers electrons through relatively thick (>50 microm) biofilms to electrodes acting as a sole electron acceptor were investigated. Biofilms of Geobacter sulfurreducens were grown either in flow-through systems with graphite anodes as the electron acceptor or on the same graphite surface, but with fumarate as the sole electron acceptor. Fumarate-grown biofilms were not immediately capable of significant current production, suggesting substantial physiological differences from current-producing biofilms.

Reclassification of Trichlorobacter thiogenes as Geobacter thiogenes comb. nov.

Reclassification of the species Trichlorobacter thiogenes as Geobacter thiogenes comb. nov. is proposed on the basis of physiological traits and phylogenetic position.

Biofilm and nanowire production leads to increased current in Geobacter sulfurreducens fuel cells.

Geobacter sulfurreducens developed highly structured, multilayer biofilms on the anode surface of a microbial fuel cell converting acetate to electricity. Cells at a distance from the anode remained viable, and there was no decrease in the efficiency of current production as the thickness of the biofilm increased. Genetic studies demonstrated that efficient electron transfer through the biofilm required the presence of electrically conductive pili.