“Hot” acetogenesis

Thermophilic microorganisms as well as acetogenic bacteria are both considered ancient. Interestingly, only a few species of bacteria, all belonging to the family Thermoanaerobacteraceae, are described to conserve energy from acetate formation with hydrogen as electron donor and carbon dioxide as electron acceptor. This review reflects the metabolic differences between Moorella spp., Thermoanaerobacter kivui and Thermacetogenium phaeum, with focus on the biochemistry of autotrophic growth and energy conservation. The potential of these thermophilic acetogens for biotechnological applications is discussed briefly.

     

A New Class of Tungsten-Containing Oxidoreductase in Caldicellulosiruptor,a Genus of Plant Biomass-Degrading Thermophilic Bacteria

Caldicellulosiruptor bescii grows optimally at 78°C and is able to decompose high concentrations of lignocellulosic plant biomass without the need for thermochemical pretreatment. C. bescii ferments both C₅ and C₆ sugars primarily to hydrogen gas, lactate, acetate, and CO₂ and is of particular interest for metabolic engineering applications given the recent availability of a genetic system. Developing optimal strains for technological use requires a detailed understanding of primary metabolism, particularly when the goal is to divert all available reductant (electrons) toward highly reduced products such as biofuels. During an analysis of the C. bescii genome sequence for oxidoreductase-type enzymes, evidence was uncovered to suggest that the primary redox metabolism of C. bescii has a completely uncharacterized aspect involving tungsten, a rarely used element in biology. An active tungsten utilization pathway in C. bescii was demonstrated by the heterologous production of a tungsten-requiring, aldehyde-oxidizing enzyme (AOR) from the hyperthermophilic archaeon Pyrococcus furiosus. Furthermore, C. bescii also contains a tungsten-based AOR-type enzyme, here termed XOR, which is phylogenetically unique, representing a completely new member of the AOR tungstoenzyme family. Moreover, in C. bescii, XOR represents ca. 2% of the cytoplasmic protein. XOR is proposed to play a key, but as yet undetermined, role in the primary redox metabolism of this cellulolytic microorganism.     

Greater epithelial ridge cells are the principal organoid-forming progenitors of the mouse cochlea

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Using a carbon-based ASM3 EAWAG Bio-P for modelling the enhanced biological phosphorus removal in anaerobic/aerobic activated sludge systems

Modelling of activated sludge processes is a commonly used technique to design and optimize wastewater treatment processes. Since wastewater and activated sludge is characterized by chemical oxygen demand (COD) measurements, units of state variables describing organic matter are expressed as equivalent amounts of COD. However, current procedures for measuring it have several drawbacks, including the production of hazardous wastes, so the utility of other variables for characterizing the organic load in modelling, such as total organic carbon (TOC), warrant re-evaluation. Other advantages of TOC over COD are that it provides matrix-independent analytical results and it can be readily measured online. Proposals for TOC-based models were made in the 1990s, but they seem to have sunk into obscurity. To re-assess the value of TOC for this purpose, we have recalculated the EAWAG module for Bio-P removal coupled to the Activated Sludge Model No. 3 on a TOC basis, and tested it against data acquired in batch experiments with four single carbon sources (acetate, glucose, citrate and casein). The batch test-based calibrations showed a good match with experimental data, following modifications of the model to account for the anaerobic volumes and retention times applied in the tests.