Metabolic alteration of Methylococcus capsulatus str. Bath during a microbial gas-phase reaction

Efficient lipidomic approach for the discovery of lipid ligands for immune receptors by combining LC-HRMS/MS analysis with fractionation and reporter cell assay

C-type lectin receptors (CLRs), which are pattern recognition receptors responsible for triggering innate immune responses, recognize damaged self-components and immunostimulatory lipids from pathogenic bacteria; however, several of their ligands remain unknown. Here, we propose a new analytical platform combining liquid chromatography-high-resolution tandem mass spectrometry with microfractionation capability (LC-FRC-HRMS/MS) and a reporter cell assay for sensitive activity measurements to develop an efficient methodology for searching for lipid ligands of CLR from microbial trace samples (crude cell extracts of approximately 5 mg dry cell/mL). We also developed an in-house lipidomic library containing accurate mass and fragmentation patterns of more than 10,000 lipid molecules predicted in silico for 90 lipid subclasses and 35 acyl side chain fatty acids. Using the developed LC-FRC-HRMS/MS system, the lipid extracts of Helicobacter pylori were separated and fractionated, and HRMS and HRMS/MS spectra were obtained simultaneously. The fractionated lipid extract samples in 96-well plates were thereafter subjected to reporter cell assays using nuclear factor of activated T cells (NFAT)-green fluorescent protein (GFP) reporter cells expressing mouse or human macrophage-inducible C-type lectin (Mincle). A total of 102 lipid molecules from all fractions were annotated using an in-house lipidomic library. Furthermore, a fraction that exhibited significant activity in the NFAT-GFP reporter cell assay contained α-cholesteryl glucoside, a type of glycolipid, which was successfully identified as a lipid ligand molecule for Mincle. Our analytical platform has the potential to be a useful tool for efficient discovery of lipid ligands for immunoreceptors.

A novel inverse membrane bioreactor for efficient bioconversion from methane gas to liquid methanol using a microbial gas-phase reaction

BACKGROUND

Methane (CH₄), as one of the major energy sources, easily escapes from the supply chain into the atmosphere, because it exists in a gaseous state under ambient conditions. Compared to carbon dioxide (CO₂), CH₄ is 25 times more potent at trapping radiation; thus, the emission of CH₄ to the atmosphere causes severe global warming and climate change. To mitigate CH₄ emissions and utilize them effectively, the direct biological conversion of CH₄ into liquid fuels, such as methanol (CH₃OH), using methanotrophs is a promising strategy. However, supplying biocatalysts in an aqueous medium with CH₄ involves high energy consumption due to vigorous agitation and/or bubbling, which is a serious concern in methanotrophic processes, because the aqueous phase causes a very large barrier to the delivery of slightly soluble gases.

RESULTS

An inverse membrane bioreactor (IMBR), which combines the advantages of gas-phase bioreactors and membrane bioreactors, was designed and constructed for the bioconversion of CH₄ into CH₃OH in this study. In contrast to the conventional membrane bioreactor with bacterial cells that are immersed in an aqueous phase, the filtered cells were placed to face a gas phase in the IMBR to supply CH₄ directly from the gas phase to bacterial cells. Methylococcus capsulatus (Bath), a representative methanotroph, was used to demonstrate the bioconversion of CH₄ to CH₃OH in the IMBR. Cyclopropanol was supplied from the aqueous phase as a selective inhibitor of methanol dehydrogenase, preventing further CH₃OH oxidation. Sodium formate was added as an electron donor to generate NADH, which is necessary for CH₃OH production. After optimizing the inlet concentration of CH₄, the mass of cells, the cyclopropanol concentration, and the gas flow rate, continuous CH₃OH production can be achieved over 72 h with productivity at 0.88 mmol L^-1 h^-1 in the IMBR, achieving a longer operation period and higher productivity than those using other types of membrane bioreactors reported in the literature.

CONCLUSIONS

The IMBR can facilitate the development of gas-to-liquid (GTL) technologies via microbial processes, allowing highly efficient mass transfer of substrates from the gas phase to microbial cells in the gas phase and having the supplement of soluble chemicals convenient.

Synthetic design of methanotroph co-cultures and their immobilization within polymers containing magnetic nanoparticles to enhance methanol production from wheat straw-based biogas

In this study, various methanotroph co-cultures were designed to enhance methanol production from biogas produced through the anaerobic digestion of wheat straw (WS). Furthermore, whole-cell immobilization was performed using magnetic nanoparticle (MNP)-loaded polymers to develop an efficient bioprocess. The anaerobic digestion of WS by cattle dung yielded 219 L/kg of total solids reduced. Methanol produced was 5.08 and 6.39 mmol/L by pure- and co-cultures from biogas, respectively. The optimization of process parameters enhanced methanol production to 6.82 mmol/L by co-culturing Mithylosinus sporium and Methylocella tundrae. The immobilized co-culture within the MNP-doped polymers exhibited much higher cumulative methanol of up to 70.74 mmol/L than the production of 22.34 mmol/L by free cells after ten cycles of reuse. This study suggests that MNP-doped polymer-based immobilization of methanotrophs is a unique approach for producing renewable fuels from biomass-derived biogas, a greenhouse gas.