Metabolic engineering of for the obligate reduction of -butyrate to -butanol.

Background: is a versatile microbe that encounters an innate redox imbalance while growing photoheterotrophically with reduced substrates. The resulting excess in reducing equivalents, together with ATP from photosynthesis, could be utilized to drive a wide range of bioconversions. The objective of this study was to genetically modify to provide a pathway to reduce -butyrate into -butanol for maintaining redox balance.

A Narrow pH Range Supports Butanol, Hexanol, and Octanol Production from Syngas in a Continuous Co-culture of and with In-Line Product Extraction.

Carboxydotrophic bacteria (CTB) have received attention due to their ability to synthesize commodity chemicals from producer gas and synthesis gas (syngas). CTB have an important advantage of a high product selectivity compared to chemical catalysts. However, the product spectrum of wild-type CTB is narrow.

Carbon recovery by fermentation of CO-rich off gases - Turning steel mills into biorefineries.

Technological solutions to reduce greenhouse gas (GHG) emissions from anthropogenic sources are required. Heavy industrial processes, such as steel making, contribute considerably to GHG emissions. Fermentation of carbon monoxide (CO)-rich off gases with wild-type acetogenic bacteria can be used to produce ethanol, acetate, and 2,3-butanediol, thereby, reducing the carbon footprint of heavy industries.

Chain Elongation with Reactor Microbiomes: Open-Culture Biotechnology To Produce Biochemicals.

Chain elongation into medium-chain carboxylates, such as n-caproate and n-caprylate, with ethanol as an electron donor and with open cultures of microbial consortia (i.e., reactor microbiomes) under anaerobic conditions is being developed as a biotechnological production platform.

Traits of selected Clostridium strains for syngas fermentation to ethanol.

Syngas fermentation is an anaerobic bioprocess that could become industrially relevant as a biorefinery platform for sustainable production of fuels and chemicals. An important prerequisite for commercialization is adequate performance of the biocatalyst (i.e.

Chain elongation in anaerobic reactor microbiomes to recover resources from waste.

Different microbial pathways can elongate the carbon chains of molecules in open cultures of microbial populations (i.e. reactor microbiomes) under anaerobic conditions.

Integrating syngas fermentation with the carboxylate platform and yeast fermentation to reduce medium cost and improve biofuel productivity.

To ensure economic implementation of syngas fermentation as a fuel-producing platform, engineers and scientists must both lower operating costs and increase product value. A considerable part of the operating costs is spent to procure chemicals for fermentation medium that can sustain sufficient growth of carboxydotrophic bacteria to convert synthesis gas (syngas: carbon monoxide, hydrogen, and carbon dioxide) into products such as ethanol. Recently, we have observed that wildtype carboxydotrophic bacteria (including Clostridium ljungdahlii) can produce alcohols with a longer carbon chain than ethanol via syngas fermentation when supplied with the corresponding carboxylic acid precursors, resulting in possibilities of increasing product value.

Upgrading dilute ethanol from syngas fermentation to n-caproate with reactor microbiomes.

Fermentation of syngas from renewable biomass, which is part of the syngas platform, is gaining momentum. Here, the objective was to evaluate a proof-of-concept bioprocessing system with diluted ethanol and acetic acid in actual syngas fermentation effluent as the substrate for chain elongation into the product n-caproic acid, which can be separated with less energy input than ethanol. Chain elongation is performed with open cultures of microbial populations (reactor microbiomes) as part of the carboxylate platform.

Biocatalytic reduction of short-chain carboxylic acids into their corresponding alcohols with syngas fermentation.

Short-chain carboxylic acids generated by various mixed- or pure-culture fermentation processes have been considered valuable precursors for production of bioalcohols. While conversion of carboxylic acids into alcohols is routinely performed with catalytic hydrogenation or with strong chemical reducing agents, here, a biological conversion route was explored. The potential of carboxydotrophic bacteria, such as Clostridium ljungdahlii and Clostridium ragsdalei, as biocatalysts for conversion of short-chain carboxylic acids into alcohols, using syngas as a source of electrons and energy is demonstrated.

Prolonged conversion of n-butyrate to n-butanol with Clostridium saccharoperbutylacetonicum in a two-stage continuous culture with in-situ product removal.

n-Butanol was produced continuously in a two-stage fermentor system with integrated product removal from a co-feed of n-butyric acid and glucose. Glucose was always required as a source of ATP and electrons for the conversion of n-butyrate to n-butanol and for biomass growth; for the latter it also served as a carbon source. The first stage generated metabolically active planktonic cells of Clostridium saccharoperbutylacetonicum strain N1-4 that were continuously fed into the second (production) stage; the volumetric ratio of the two fermentors was 1:10.

Role of secondary transporters and phosphotransferase systems in glucose transport by Oenococcus oeni.

Glucose uptake by the heterofermentative lactic acid bacterium Oenococcus oeni B1 was studied at the physiological and gene expression levels. Glucose- or fructose-grown bacteria catalyzed uptake of [(14)C]glucose over a pH range from pH 4 to 9, with maxima at pHs 5.5 and 7.

Genome-scale dynamic modeling of the competition between Rhodoferax and Geobacter in anoxic subsurface environments.

The advent of rapid complete genome sequencing, and the potential to capture this information in genome-scale metabolic models, provide the possibility of comprehensively modeling microbial community interactions. For example, Rhodoferax and Geobacter species are acetate-oxidizing Fe(III)-reducers that compete in anoxic subsurface environments and this competition may have an influence on the in situ bioremediation of uranium-contaminated groundwater. Therefore, genome-scale models of Geobacter sulfurreducens and Rhodoferax ferrireducens were used to evaluate how Geobacter and Rhodoferax species might compete under diverse conditions found in a uranium-contaminated aquifer in Rifle, CO.

Electricity generation by Geobacter sulfurreducens attached to gold electrodes.

The versatility of gold for electrode manufacture suggests that it could be an ideal material for some microbial fuel cell applications. However, previous studies have suggested that microorganisms that readily transfer electrons to graphite do not transfer electrons to gold. Investigations with Geobacter sulfurreducens demonstrated that it could grow on gold anodes producing current nearly as effectively as with graphite anodes.

Lack of electricity production by Pelobacter carbinolicus indicates that the capacity for Fe(III) oxide reduction does not necessarily confer electron transfer ability to fuel cell anodes.

The ability of Pelobacter carbinolicus to oxidize electron donors with electron transfer to the anodes of microbial fuel cells was evaluated because microorganisms closely related to Pelobacter species are generally abundant on the anodes of microbial fuel cells harvesting electricity from aquatic sediments. P. carbinolicus could not produce current in a microbial fuel cell with electron donors which support Fe(III) oxide reduction by this organism.

Pyruvate fermentation by Oenococcus oeni and Leuconostoc mesenteroides and role of pyruvate dehydrogenase in anaerobic fermentation.

The heterofermentative lactic acid bacteria Oenococcus oeni and Leuconostoc mesenteroides are able to grow by fermentation of pyruvate as the carbon source (2 pyruvate --> 1 lactate + 1 acetate + 1 CO(2)). The growth yields amount to 4.0 and 5.

Significance of phosphoglucose isomerase for the shift between heterolactic and mannitol fermentation of fructose by Oenococcus oeni.

The bacterium Oenococcus oeni employs the heterolactic fermentation pathway (products lactate, ethanol, CO(2)) during growth on fructose as a substrate, and the mannitol pathway when using fructose as an electron acceptor. In this study, [U-(13)C]glucose, [U-(13)C]fructose, HPLC, NMR spectroscopy, and enzyme analysis were applied to elucidate the use of both pathways by the hexoses. In the presence of glucose or pyruvate, fructose was metabolized either by the mannitol or the phosphoketolase pathways, respectively.

Vulnerability curves from conifer sapwood sections exposed over solutions with known water potentials.

The cohesion-tension (CT) theory requires stability of liquid water in conducting elements under high tensions. This stability has been measured using different methods, some of which yielded contradictory results. In this study a method is presented to establish known tensions in the water inside conifer tracheids, to detect cavitation events under these conditions and to construct vulnerability curves.

Use of the mannitol pathway in fructose fermentation of Oenococcus oeni due to limiting redox regeneration capacity of the ethanol pathway.

The heterolactic bacterium Oenococcus oeni ferments fructose by a mixed heterolactic/mannitol fermentation. For heterolactic fermentation of fructose, the phosphoketolase pathway is used. The excess NAD(P)H from the phosphoketolase pathway is reoxidized by fructose (yielding mannitol).

A new method to determine the oxygen concentration inside the sapwood of trees.

Research into the short-term fluctuations of oxygen concentrations in tree stems has been hampered by the difficulty of measuring oxygen inside tissues. A new method, which is based on fluorescence quenching of a ruthenium complex in the presence of oxygen, has been applied to measure changes of oxygen concentration in the sapwood of trees. During a field day-course oxygen increased with the radiation load and fell during the night (in Fagus orientalis from 20.