Staphylococcus aureus does not synthesize arginine from proline under physiological conditions

The Gram-positive pathogen Staphylococcus aureus is the only bacterium known to synthesize arginine from proline via the arginine-proline interconversion pathway, despite having genes for the well-conserved glutamate pathway. Since the proline-arginine interconversion pathway is repressed by CcpA-mediated carbon catabolite repression (CCR), CCR has been attributed to the arginine auxotrophy of S. aureus. Using ribose as a secondary carbon source, here, we demonstrate that S. aureus arginine auxotrophy is not due to CCR but due to the inadequate concentration of proline degradation product. Proline is degraded by proline dehydrogenase (PutA) into pyrroline-5-carboxylate (P5C). Although the PutA expression was fully induced by ribose, the P5C concentration remained insufficient to support arginine synthesis because P5C was constantly consumed by the P5C reductase ProC. When the P5C concentration was artificially increased by either PutA overexpression or proC-deletion, S. aureus could synthesize arginine from proline regardless of carbon source. In contrast, when the P5C concentration was reduced by overexpression of proC, it inhibited the growth of the ccpA-deletion mutant without arginine. Intriguingly, the ectopic expression of the glutamate pathway enzymes converted S. aureus into arginine prototroph. In an animal experiment, the arginine-proline interconversion pathway was not required for the survival of S. aureus. Based on these results, we concluded that S. aureus does not synthesize arginine from proline under physiological conditions. We also propose that arginine auxotrophy of S. aureus is not due to the CcpA-mediated CCR but due to the inactivity of the conserved glutamate pathway.

Study of Chinese carbon emission trading market mechanism based on the game theory

<p>In order to provide corresponding suggestions for the establishment and development of China's carbon trading market mechanism, the three-party game model of the competent government departments, carbon emission enterprises and third-party verification institution in the initial allocation of carbon emission rights and the rotation bargaining game model in the secondary carbon trading market are solved and analyzed in this paper. The results show that the competent government departments should improve the review efficiency effectively to reduce cost by outsourcing the review work to universities, research institutes and other scientific research units and increasing punishment for the collusion behavior between the carbon emission enterprises and third-party verification institution. At the same time, the competent government departments should adopt the regular regulatory policies to deal with collusion behavior and reduce the sampling proportion to cut cost of government review. The trading center should directly determine transaction price in combination with the forces of buyers and sellers, and make matchmaking trading directly by selecting the qualified buyers and sellers at the secondary carbon trading market in process of bilateral open bidding.</p>

Production of Polyhydroxyalkanoates (PHAs) by Vibrio alginolyticus Strains Isolated from Salt Fields

Vibrio alginolyticus is a halophilic organism usually found in marine environments. It has attracted attention as an opportunistic pathogen of aquatic animals and humans, but there are very few reports on polyhydroxyalkanoate (PHA) production using V. alginolyticus as the host. In this study, two V. alginolyticus strains, LHF01 and LHF02, isolated from water samples collected from salt fields were found to produce poly(3-hydroxybutyrate) (PHB) from a variety of sugars and organic acids. Glycerol was the best carbon source and yielded the highest PHB titer in both strains. Further optimization of the NaCl concentration and culture temperature improved the PHB titer from 1.87 to 5.08 g/L in V. alginolyticus LHF01. In addition, the use of propionate as a secondary carbon source resulted in the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). V. alginolyticus LHF01 may be a promising host for PHA production using cheap waste glycerol from biodiesel refining.

PAOX1 expression in mixed-substrate continuous cultures of Komagataella phaffii (Pichia pastoris) is completely determined by methanol uptake regardless of the secondary carbon source: a simplifying principle for predicting recombinant protein production.

The expression of recombinant proteins by the AOX1 promoter of Komagataella phaffii is typically induced by adding methanol to the cultivation medium. Since growth on methanol imposes a high oxygen demand, the medium is often supplemented with an additional "secondary" carbon source which serves to reduce the consumption of methanol, and hence, oxygen. Early research recommended the use of glycerol as the secondary carbon source, but more recent studies recommend the use of sorbitol because glycerol represses PAOX1 expression. To assess the validity of this recommendation, we measured the steady state concentrations of biomass, residual methanol, and AOX1 over a wide range of dilution rates (0.02-0.20 h-1) in continuous cultures of the Mut+ strain fed with methanol, methanol + glycerol, and methanol + sorbitol. We find that when the specific AOX1 expression and methanol uptake rates for each of the three feeds are plotted against each other, they collapse into a single hyperbolic curve. The specific AOX1 expression rate is therefore completely determined by the specific methanol uptake rate regardless of the existence (present/absent) and type (repressing/non-repressing) of the secondary carbon source. In particular, cultures fed with methanol + glycerol and methanol + sorbitol that consume methanol at equal rates also express the protein at equal rates and levels. Now, it turns out that the simple unstructured model developed by Egli and co-workers can predict the specific methanol uptake rates of single- and mixed-substrate cultures over a wide range of dilution rates and feed concentrations. By combining this model with our data, we derive simple formulas that predicts the protein expression rates and levels of single- and mixed-substrate cultures over a wide range of conditions.

Separation of Th from leachate of monazite sulphation process using amine solvent extraction

The solvent extraction is one of the most common method for separating Th from solution. Primary amine has higher selectivity for the extraction of Th(IV) than U(VI) and RE(III) in sulfate media. N1923 (a primary aliphatic amine with amino nitrogen linked to a secondary carbon consisting of branched alkyl groups in C19–23 range) is commonly used to extractTh. At room temperature using 0.1M N1923 amine as solvent in this work, the results showed thatthorium maximum extraction capacity was about 2.5g/L with concentration of sulfuric acid in the aqueous phase was 1M and for 3 minutes shaking. At room temperature for 3 minutes shaking the best conditions for scrubbing processwas using the mixture of acids H2SO4 0.2M and HNO3 0.1M, result inover 75%, Th was scrubbed in the aqueous phase only 0.7%. The separation of Th from leachate of monazite sulphation process was carried out on a multistage continuous flow extraction device (12 boxes), the thorium purity was 98%. Therefore, the use of amine solvents can purify thorium from rare-earth solutions in a sulfate medium

Effect of Secondary Carbon Nanofillers on the Electrical, Thermal, and Mechanical Properties of Conductive Hybrid Composites Based on Epoxy Resin and Graphite

In this work, we present a comparative study of the impact of secondary carbon nanofillers on the electrical and thermal conductivity, thermal stability, and mechanical properties of hybrid conductive polymer composites (CPC) based on high loadings of synthetic graphite and epoxy resin. Two different carbon nanofillers were chosen for the investigation—low-cost multi-layered graphene nanoplatelets (GN) and carbon black (CB), which were aimed at improving the overall performance of composites. The samples were obtained by a simple, inexpensive, and effective compression molding technique, and were investigated by the means of, i.a., scanning electron microscopy, Raman spectroscopy, electrical conductivity measurements, laser flash analysis, and thermogravimetry. The tests performed revealed that, due to the exceptional electronic transport properties of GN, its relatively low specific surface area, good aspect ratio, and nanometric sizes of particles, a notable improvement in the overall characteristics of the composites (best results for 4 wt % of GN; σ = 266.7 S cm−1; λ = 40.6 W mK−1; fl. strength = 40.1 MPa). In turn, the addition of CB resulted in a limited improvement in mechanical properties, and a deterioration in electrical and thermal properties, mainly due to the too high specific surface area of this nanofiller. The results obtained were compared with US Department of Energy recommendations regarding properties of materials for bipolar plates in fuel cells. As shown, the materials developed significantly exceed the recommended values of the majority of the most important parameters, indicating high potential application of the composites obtained.

Thermonuclear explosion of a massive hybrid HeCO white-dwarf triggered by a He-detonation on a companion

Normal type Ia supernovae (SNe) are thought to arise from the thermonuclear explosion of massive (&gt;0.8 M⊙) carbon-oxygen white dwarfs (WDs), although the exact mechanism is debated. In some models helium accretion on to a carbon-oxygen (CO) WD from a companion was suggested to dynamically trigger a detonation of the accreted helium shell. The helium detonation then produces a shock that after converging on itself close to the core of the CO-WD, triggers a secondary carbon detonation and gives rise to an energetic explosion. However, most studies of such scenarios have been done in one or two dimensions, and/or did not consider self-consistent models for the accretion and the He-donor. Here we make use of detailed 3D simulation to study the interaction of a He-rich hybrid 0.69 M⊙ HeCO WD with a more massive 0.8 M⊙ CO WD. We find that accretion from the hybrid WD on to the CO WD gives rise to a helium detonation. However, the helium detonation does not trigger a carbon detonation in the CO WD. Instead, the helium detonation burns through the accretion stream to also burn the helium shell of the donor hybrid HeCO-WD. The detonation of its massive helium shell then compresses its CO core, and triggers its detonation and full destruction. The explosion gives rise to a faint, likely highly reddened transient, potentially observable by the Vera Rubin survey, and the high-velocity (∼1000 kms−1) ejection of the heated surviving CO WD companion. Pending on uncertainties in stellar evolution we estimate the rate of such transient to be up to $\sim 10{{\ \rm per\ cent}}$ of the rate of type Ia SNe.

Green and sustainable molten salt electrochemistry for the conversion of secondary carbon pollutants to advanced carbon materials

Carbon emissions have cause serious climate change such as global warming, glacier melting, and sea level rise and so on. Carbon neutrality becomes a global target and the sustainable disposal...