Mass transfer characterization of an airlift probe for oxygenating and mixing cell suspensions in an NMR spectrometer

Biological hydrogen methanation - A review

Surplus energy out of fluctuating energy sources like wind and solar energy is strongly increasing. Biological hydrogen (H₂) methanation (BHM) is a highly promising approach to move the type of energy from electricity to natural gas via electrolysis and the subsequent step of the Sabatier-reaction. This review provides an overview of the numerous studies concerning the topic of BHM. The technical and biological parameters regarding the research results of these studies are compared and analyzed hereafter. A holistic view on how to overcome physical limitations of the fermentation process, such as gas-liquid mass transfer or a rise of the pH value, and on the enhancement of environmental circumstances for the bacterial biomass are delivered within. With regards to ex-situ methanation, the evaluated studies show a distinct connection between methane production and the methane percentage in the off-gas.

Optimization of hydrogen dispersion in thermophilic up-flow reactors for ex situ biogas upgrading

This study evaluates the efficiency of four novel up-flow reactors for ex situ biogas upgrading converting externally provided CO₂ and H₂ to CH₄, via hydrogenotrophic methanogenesis. The gases were injected through stainless steel diffusers combined with alumina ceramic sponge or through alumina ceramic membranes. Pore size, input gas loading and gas recirculation flow rate were modulated to optimize gas-liquid mass transfer, and thus methanation efficiency. Results showed that larger pore size diffusion devices achieved the best kinetics and output-gas quality converting all the injected H₂ and CO₂, up to 3.6L/L_REACTOR·d H₂ loading rate. Specifically, reactors' CH₄ content increased from 23 to 96% and the CH₄ yield reached 0.25L_CH4/L_H2. High throughput 16S rRNA gene sequencing revealed predominance of bacteria belonging to Anaerobaculum genus and to uncultured order MBA08. Additionally, the massive increase of hydrogenotrophic methanogens, such as Methanothermobacter thermautotrophicus, and syntrophic bacteria demonstrates the selection-effect of H₂ on community composition.

In-situ biogas upgrading in thermophilic granular UASB reactor: key factors affecting the hydrogen mass transfer rate

Biological biogas upgrading coupling CO₂ with external H₂ to form biomethane opens new avenues for sustainable biofuel production. For developing this technology, efficient H₂ to liquid transfer is fundamental. This study proposes an innovative setup for in-situ biogas upgrading converting the CO₂ in the biogas into CH₄, via hydrogenotrophic methanogenesis. The setup consisted of a granular reactor connected to a separate chamber, where H₂ was injected. Different packing materials (rashig rings and alumina ceramic sponge) were tested to increase gas-liquid mass transfer. This aspect was optimized by liquid and gas recirculation and chamber configuration. It was shown that by distributing H₂ through a metallic diffuser followed by ceramic sponge in a separate chamber, having a volume of 25% of the reactor, and by applying a mild gas recirculation, CO₂ content in the biogas dropped from 42 to 10% and the final biogas was upgraded from 58 to 82% CH₄ content.

Development of a small-scale bioreactor: application to in vivo NMR measurement

A perfused bioreactor allowing in vivo NMR measurement was developed and validated for Eschscholtzia californica cells. The bioreactor was made of a 10-mm NMR tube. NMR measurement of the signal-to-noise ratio was optimized using a sedimented compact bed of cells that were retained in the bioreactor by a supporting filter. Liquid medium flow through the cell bed was characterized from a mass balance on oxygen and a dispersive hydrodynamic model. Cell bed oxygen demand for 4 h perfusion required a minimal medium flow rate of 0.8 mL/min. Residence time distribution assays at 0.8-2.6 mL/min suggest that the cells are subjected to a uniform nutrient environment along the cell bed. Cell integrity was maintained for all culture conditions since the release of intracellular esterases was not significant even after 4 h of perfusion. In vivo NMR was performed for (31)P NMR and the spectrum can be recorded after only 10 min of spectral accumulation (500 scans) with peaks identified as G-6P, F-6P, cytoplasmic Pi, vacuolar Pi, ATP(gamma) and ADP(beta), ATP(alpha) and ADP(alpha), NADP and NDPG, NDPG and ATP(beta). Cell viability was shown to be maintained as (31)P chemical shifts were constant with time for all the identified nuclei, thus suggesting constant intracellular pH.

Multiple formate dehydrogenase enzymes in the facultative methylotroph Methylobacterium extorquens AM1 are dispensable for growth on methanol

Formate dehydrogenase has traditionally been assumed to play an essential role in energy generation during growth on C(1) compounds. However, this assumption has not yet been experimentally tested in methylotrophic bacteria. In this study, a whole-genome analysis approach was used to identify three different formate dehydrogenase systems in the facultative methylotroph Methylobacterium extorquens AM1 whose expression is affected by either molybdenum or tungsten. A complete set of single, double, and triple mutants was generated, and their phenotypes were analyzed. The growth phenotypes of the mutants suggest that any one of the three formate dehydrogenases is sufficient to sustain growth of M. extorquens AM1 on formate, while surprisingly, none is required for growth on methanol or methylamine. Nuclear magnetic resonance analysis of the fate of [(13)C]methanol revealed that while cells of wild-type M. extorquens AM1 as well as cells of all the single and the double mutants continuously produced [(13)C]bicarbonate and (13)CO(2), cells of the triple mutant accumulated [(13)C]formate instead. Further studies of the triple mutant showed that formate was not produced quantitatively and was consumed later in growth. These results demonstrated that all three formate dehydrogenase systems must be inactivated in order to disrupt the formate-oxidizing capacity of the organism but that an alternative formate-consuming capacity exists in the triple mutant.

In vivo 13C-NMR studies of polymer synthesis in rhizobium meliloti M5N1 strain

The use of in vivo 13C-NMR approach for the monitoring of the synthesis of various polymers within cells of Rhizobium meliloti (M5N1 strain) is reported. Significant differences in polymer biosynthesis have been shown as a function of the metabolic state of the cells and the labeled carbon source used. Consumption of carbon source and produced glycogen was complete with mid-exponential phase harvested cells. This was not the case with stationary phase harvested cells, for which polyhydroxybutyrate synthesis was higher and gluconate synthesis was lower than the former. [1-13C]fructose-grown cells produced more exopolysaccharide and polyhydroxybutyrate, but less beta-(1,2) glucan and gluconate than [1-13C]glucose-grown cells. This approach offers a suitable tool to examine the kinetics of polymer biosynthesis by Rhizobia. Copyright 1998 John Wiley & Sons, Inc.

Reaction engineering methods to study intracellular metabolite concentrations

The analysis of intracellular metabolite concentrations is of basic importance for metabolic engineering of microorganisms. In vivo NMR-spectroscopy as a non-invasive technique to measure intracellular metabolite concentrations and rapid sampling devices as invasive techniques are reviewed. The methods are discussed from a reaction engineering point of view. The objective is to obtain intracellular concentration data under well defined physiological conditions in balanced steady state and defined transitional states as well. Application examples are given for a membrane-cyclone-reactor configuration designed to achieve high signal sensitivity with in vivo 31P-NMR and 13C-NMR spectroscopy as well as for a sampling tube device designed for high sampling rates (2s-1). This sampling device enables the measurement of dynamic metabolite profiles at a time scale of a few seconds.

A new NMR airlift bioreactor used in 31P-NMR studies of itaconic acid producing Aspergillus terreus

An airlift bioreactor for in-vivo NMR studies of cells is described. The 10-mm diameter airlift reactor was constructed for studies of mycelial/pellet forming organisms, grown in suspension. With this device 161 MHz 31P-NMR spectra of living Aspergillus terreus cells, producing itaconic acid, have been obtained. Signals were observed for intra- and extracellular orthophosphate, glycerol-3-phosphorylethanolamine (GPE), glycerol-3-phosphorylcholine (GPC), sugar phosphates and polyphosphate. The spectra also showed broad overlapping resonances in the shift range of NAD(H) and NADP(H). Polyphosphate disappeared when the respiratory gas was exchanged for pure N2. The intracellular pH was estimated at 6.2. In spectra of cell extracts approx. 60 peaks were observed in the range of 20 to -22 ppm, and they confirmed the appearance of the metabolites observed in living cells.