Hydrogen production in an aerobic environment by Escherichia coli K-12

Escherichia coli (E. coli) is a facultative anaerobe that can grow in a variety of environmental conditions. In the complete absence of O2, E. coli can perform a mixed-acid fermentation that contains within it an elaborate metabolism of formic acid. In this study, we use cavity-enhanced Raman spectroscopy (CERS), FTIR, liquid Raman spectroscopy, isotopic labelling, and molecular genetics to make advances in the understanding of bacterial formate and H2 metabolism. It is shown that, under anaerobic conditions, formic acid is generated endogenously, excreted briefly from the cell, and then taken up again to be disproportionated to H2 and CO2 by formate hydrogenlyase (FHL-1). However, exogenously added D-labelled formate behaves quite differently from the endogenous formate and is taken up immediately, independently, and possibly by a different mechanism, by the cell and converted to H2 and CO2. Our data support an anion-proton symport model for formic acid transport. In addition, when E. coli was grown in a microaerobic environment it was possible to analyse aspects of formate and O2 respiration occurring alongside anaerobic metabolism. While cells growing under microaerobic conditions generated endogenous formic acid, no H2 was produced. However, addition of exogenous formate at the outset of cell growth did induce FHL-1 biosynthesis and resulted in formate-dependent H2 production in the presence of O2.

Biosynthesis of Poly-(3-hydroxybutyrate) under the Control of an Anaerobically Induced Promoter by Recombinant Escherichia coli from Sucrose

Poly-(3-hydroxybutyrate) (PHB) is a polyester with biodegradable and biocompatible characteristics and has many potential applications. To reduce the raw material costs and microbial energy consumption during PHB production, cheaper carbon sources such as sucrose were evaluated for the synthesis of PHB under anaerobic conditions. In this study, metabolic network analysis was conducted to construct an optimized pathway for PHB production using sucrose as the sole carbon source and to guide the gene knockout to reduce the generation of mixed acid byproducts. The plasmid pMCS-sacC was constructed to utilize sucrose as a sole carbon source, and the cascaded promoter P3nirB was used to enhance PHB synthesis under anaerobic conditions. The mixed acid fermentation pathway was knocked out in Escherichia coli S17-1 to reduce the synthesis of byproducts. As a result, PHB yield was improved to 80% in 6.21 g/L cell dry weight by the resulted recombinant Escherichia coli in a 5 L bed fermentation, using sucrose as the sole carbon source under anaerobic conditions. As a result, the production costs of PHB will be significantly reduced.

NMR metabolomics of symbioses between bacterial vaginosis associated bacteria

Bacterial vaginosis (BV) is a dysbiosis of the vaginal microbiome, characterised by low levels of lactobacilli and overgrowth of a diverse group of bacteria, and associated with higher risk of a variety of infections, surgical complications, cancer and spontaneous preterm birth (PTB). Despite the lack of a consistently applicable aetiology, Prevotella spp. are often associated with both BV and PTB and P. bivia has known symbiotic relationships with both Peptostreptococcus anaerobius and Gardnerella vaginalis. Higher risk of PTB can also be predicted by a composite of metabolites linked to bacterial metabolism but their specific bacterial source remains poorly understood. Here we characterise diversity of metabolic strategies among BV associated bacteria and lactobacilli and the symbiotic metabolic relationships between P. bivia and its partners and show how these influence the availability of metabolites associated with BV/PTB and/or pro- or anti-inflammatory immune responses. We confirm a commensal relationship between Pe. anaerobius and P. bivia, refining its mechanism; P. bivia supplies tyrosine, phenylalanine, methionine, uracil and proline, the last of which leads to a substantial increase in overall acetate production. In contrast, our data indicate the relationship between P. bivia and G. vaginalis strains, with sequence variant G2, is mutualistic with outcome dependent on the metabolic strategy of the G. vaginalis strain. Seven G. vaginalis strains could be separated according to whether they performed mixed acid fermentation (MAF) or bifid shunt (BS). In co-culture, P. bivia supplies all G. vaginalis strains with uracil and received substantial amounts of asparagine in return. Acetate production, which is lower in BS strains, then matched that of MAF strains while production of aspartate increased for the latter. Taken together, our data show how knowledge of inter- and intra-species metabolic diversity and the effects of symbiosis may refine our under-standing of the mechanism and approach to risk prediction in BV and/or PTB.

Catalytic Synthesis of the Biofuel 5-Ethoxymethylfurfural (EMF) from Biomass Sugars

A new generation of bioplatform molecule 5-ethoxymethylfurfural (EMF) has excellent energy density and combustion performance, which makes it a potential fuel additive. This article reviews the factors that affect the production of EMF from different feedstocks, including platform compounds, monosaccharides, polysaccharides, and raw lignocellulosic biomass. Focus is placed on discussing the catalytic efficiency with pros and cons of different acid catalysts, including homogeneous catalysts (i.e., liquid acids and metal salts), heterogeneous catalysts (i.e., zeolites, heteropolyacid-based hybrids, and SO3H-based catalysts), ionic liquids, mixed acid catalysts, and deep eutectic solvents (DESs). Except for the commonly used ethanol solvent, this review also summarizes the influence of the cosolvent system (e.g., ethanol/dimethylsulfoxide (DMSO), ethanol/tetrahydrofuran (THF), and ethanol/γ-valerolactone (GVL)) on the EMF yield.

Vaginal and Anal Microbiome during Chlamydia trachomatis Infections

Background. Chlamydia trachomatis (CT) is the agent of the most common bacterial sexually transmitted infection worldwide, with a significant impact on women’s health. Despite the increasing number of studies about the vaginal microbiome in women with CT infections, information about the composition of the anal microbiome is still lacking. Here, we assessed the bacterial community profiles of vaginal and anal ecosystems associated or not with CT infection in a cohort of Caucasian young women. Methods. A total of 26 women, including 10 with a contemporary vaginal and ano-rectal CT infection, were enrolled. Composition of vaginal and anal microbiome was studied by 16S rRNA gene profiling. Co-occurrence networks of bacterial communities and metagenome metabolic functions were determined. Results. In case of CT infection, both vaginal and anal environments were characterized by a degree of dysbiosis. Indeed, the vaginal microbiome of CT-positive women were depleted in lactobacilli, with a significant increase in dysbiosis-associated bacteria (e.g., Sneathia, Parvimonas, Megasphaera), whereas the anal microbiota of CT-infected women was characterized by higher levels of Parvimonas and Pseudomonas and lower levels of Escherichia. Interestingly, the microbiome of anus and vagina had numerous bacterial taxa in common, reflecting a significant microbial ‘sharing’ between the two sites. In the vaginal environment, CT positively correlated with Ezakiella spp. while Gardnerella vaginalis co-occurred with several dysbiosis-related microbes, regardless of CT vaginal infection. The vaginal microbiome of CT-positive females exhibited a higher involvement of chorismate and aromatic amino acid biosynthesis, as well as an increase in mixed acid fermentation. Conclusions. These data could be useful to set up new diagnostic/prognostic tools, offering new perspectives for the control of chlamydial infections.

Histological Evaluation of Porous Additive-Manufacturing Titanium Artificial Bone in Rat Calvarial Bone Defects

Jaw reconstruction using an additive-manufacturing titanium artificial bone (AMTAB) has recently attracted considerable attention. The synthesis of a titanium artificial bone is based on three-dimensional computed tomography images acquired before surgery. A histological evaluation of porous AMTAB (pAMTAB) embedded in rat calvarial bone defects was conducted. This study examined three groups: rats implanted with mixed-acid and heat-treated pAMTAB, rats implanted with untreated pAMTAB, and rats with no implant. In both pAMTAB groups, bone defects were created in rat calvarial bones using a 5-mm trephine bar, followed by pAMTAB implantation. The pAMTAB was fixed to the defect using the fitting force of the surrounding bones. The rats were sacrificed at 4, 8, and 16 weeks after implantation, and the skull was dissected. Undecalcified ground slides were prepared and stained with Villanueva Goldner. Compared with the no implant control group, both pAMTAB groups exhibited new bone formation inside the defect, with greater bone formation in the mixed-acid and heat-treated pAMTAB group than in the untreated pAMTAB group, but the difference was not significant. These data suggest that pAMTAB induces bone formation after implantation in bone defects. Bone formation appears to be enhanced by prior mixed-acid and heat-treated pAMTAB.

Simulation of flow field characteristics in scheelite leaching tank with H2SO4–H3PO4

Digesting scheelite by using H2SO4–H3PO4 is an environment-friendly and low-cost technology. The key approach to achieving efficient scheelite decomposition involves providing a good environment with uniform material composition for the growth of calcium sulfate. Therefore, numerical simulation of gypsum particle suspensions in a square stirred tank with a frame-type agitator for leaching scheelite was investigated. Simulated optimized results showed that the homogeneity of a multiphase flow system increased with the speed of the agitator. Reducing off-bottom clearance eased the dispersion of gypsum into the liquid. Adding baffles increased turbulence intensity and axial velocity in the tank, which eased solid suspension. The suspension improved, together with increases in the torque and power requirements of the agitator when the speed changed and baffled were added. However, when the solid suspension improved, the stirring torque and power slightly decreased, under a different off-bottom clearance of the agitator. Meanwhile, with residence time distribution as an evaluation criterion, the experimental results verified that the flow characteristics of the solid particles improved after optimization. This study can provide a theoretical basis and guidance for the optimization of the design and enlargement test of the stirred tank for leaching scheelite with sulfuric–phosphorous mixed acid.

Mixed Acid Fermentation of Carbohydrate-Rich Dairy Manure Hydrolysate

Dairy manure (DM) is an abundant agricultural residue that is largely composed of lignocellulosic biomass. The aim of this study was to investigate if carbon derived from DM fibers can be recovered as medium-chain fatty acids (MCFAs), which are mixed culture fermentation products of economic interest. DM fibers were subjected to combinations of physical, enzymatic, chemical, and thermochemical pretreatments to evaluate the possibility of producing carbohydrate-rich hydrolysates suitable for microbial fermentation by mixed cultures. Among the pretreatments tested, decrystalization dilute acid pretreatment (DCDA) produced the highest concentrations of glucose and xylose, and was selected for further experiments. Bioreactors fed DCDA hydrolysate were operated. Acetic acid and butyric acid comprised the majority of end products during operation of the bioreactors. MCFAs were transiently produced at a maximum concentration of 0.17 mg CODMCFAs/mg CODTotal. Analyses of the microbial communities in the bioreactors suggest that lactic acid bacteria, Megasphaera, and Caproiciproducens were involved in MCFA and C4 production during DCDA hydrolysate metabolism.