The diversity of mucin-degrading bacteria in the human intestine was investigated by combining culture and 16S rRNA-dependent approaches. A dominant bacterium, strain Muc T , was isolated by dilution to extinction of faeces in anaerobic medium containing gastric mucin as the sole carbon and nitrogen source. A pure culture was obtained using the anaerobic soft agar technique. Strain Muc T was a Gram-negative, strictly anaerobic, non-motile, non-spore-forming, oval-shaped bacterium that could grow singly and in pairs. When grown on mucin medium, cells produced a capsule and were found to aggregate. Strain Muc T could grow on a limited number of sugars, including N-acetylglucosamine, N-acetylgalactosamine and glucose, but only when a protein source was provided and with a lower growth rate and final density than on mucin. The G+C content of DNA from strain Muc T was 47?6 mol%. 16S rRNA gene sequence analysis revealed that the isolate was part of the division Verrucomicrobia. The closest described relative of strain Muc T was Verrucomicrobium spinosum (92 % sequence similarity). Remarkably, the 16S rRNA gene sequence of strain Muc T showed 99 % similarity to three uncultured colonic bacteria.

Interspecies electron transfer is a key process in methanogenic and sulphate-reducing environments. Bacteria and archaea that live in syntrophic communities take advantage of the metabolic abilities of their syntrophic partner to overcome energy barriers and break down compounds that they cannot digest by themselves. Here, we review the transfer of hydrogen and formate between bacteria and archaea that helps to sustain growth in syntrophic methanogenic communities. We also describe the process of reverse electron transfer, which is a key requirement in obligately syntrophic interactions. Anaerobic methane oxidation coupled to sulphate reduction is also carried out by syntrophic communities of bacteria and archaea but, as we discuss, the exact mechanism of this syntrophic interaction is not yet understood.

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. The goal is to use the high thermodynamic efficiency of anaerobic fermentation to convert organic biomass or organic wastes into valuable biochemicals that can be extracted. Several liter-scale studies have been completed and a first pilot-plant study is underway. However, the underlying microbial pathways are not always well understood. In addition, an interdisciplinary approach with knowledge from fields ranging from microbiology and chemical separations to biochemistry and environmental engineering is required. To bring together research from different fields, we reviewed the literature starting with the microbiology and ending with the bioprocess engineering studies that already have been performed. Because understanding the microbial pathways is so important to predict and steer performance, we delved into a stoichiometric and thermodynamic model that sheds light on the effect of substrate ratios and environmental conditions on product formation. Finally, we ended with an outlook.

Carbon dioxide (CO2) is a kinetically and thermodynamically stable molecule. It is easily formed by the oxidation of organic molecules, during combustion or respiration, but is difficult to reduce. The production of reduced carbon compounds from CO 2 is an attractive proposition, because carbon-neutral energy sources could be used to generate fuel resources and sequester CO 2 from the atmosphere. However, available methods for the electrochemical reduction of CO2 require excessive overpotentials (are energetically wasteful) and produce mixtures of products. Here, we show that a tungsten-containing formate dehydrogenase enzyme (FDH1) adsorbed to an electrode surface catalyzes the efficient electrochemical reduction of CO 2 to formate. Electrocatalysis by FDH1 is thermodynamically reversible-only small overpotentials are required, and the point of zero net catalytic current defines the reduction potential. It occurs under thoroughly mild conditions, and formate is the only product. Both as a homogeneous catalyst and on the electrode, FDH1 catalyzes CO 2 reduction with a rate more than two orders of magnitude faster than that of any known catalyst for the same reaction. Formate oxidation is more than five times faster than CO 2 reduction. Thermodynamically, formate and hydrogen are oxidized at similar potentials, so formate is a viable energy source in its own right as well as an industrially important feedstock and a stable intermediate in the conversion of CO2 to methanol and methane. FDH1 demonstrates the feasibility of interconverting CO2 and formate electrochemically, and it is a template for the development of robust synthetic catalysts suitable for practical applications.electrocatalysis ͉ formate dehydrogenase ͉ formate oxidation ͉ protein film voltammetry ͉ carbon dioxide reduction C arbon dioxide (CO 2 ) is a kinetically and thermodynamically stable molecule that is difficult to chemically activate. As the unreactive product of the combustion of carbon-containing molecules, such as fossil fuels, and biological respiration, it is accumulating in the atmosphere and is a major cause of concern in climate-change scenarios (1, 2). Consequently, catalysts that are able to sequester CO 2 from the atmosphere rapidly and efficiently, to generate reduced carbon compounds for use as fuels or chemical feedstocks, have long been sought after. Organometallic complexes that insert CO 2 into an M-H bond and the use of supercritical CO 2 to facilitate its hydrogenation are two promising approaches to the development of a homogeneous catalytic process (3-5). Extensive efforts to develop electrode materials for the direct, electrochemical reduction of CO 2 have been made also, but so far, they require the application of extreme potentials (are inefficient energetically) or they are nonspecific and produce mixtures of products (4, 6, 7). An efficient and specific method for reducing CO 2 electrochemically has obvious applications in a future energy economy based on the cyclic reduction and oxidation of simple carbon compound...

Intestinal bacteria influence mammalian physiology, but many types of bacteria are still uncharacterized. Moreover, reference strains of mouse gut bacteria are not easily available, although mouse models are extensively used in medical research. These are major limitations for the investigation of intestinal microbiomes and their interactions with diet and host. It is thus important to study in detail the diversity and functions of gut microbiota members, including those colonizing the mouse intestine. To address these issues, we aimed at establishing the Mouse Intestinal Bacterial Collection (miBC), a public repository of bacterial strains and associated genomes from the mouse gut, and studied host-specificity of colonization and sequence-based relevance of the resource. The collection includes several strains representing novel species, genera and even one family. Genomic analyses showed that certain species are specific to the mouse intestine and that a minimal consortium of 18 strains covered 50-75% of the known functional potential of metagenomes. The present work will sustain future research on microbiota-host interactions in health and disease, as it will facilitate targeted colonization and molecular studies. The resource is available at www.dsmz.de/miBC.