A novel pyruvate kinase and its application in lactic acid production under oxygen deprivation in Corynebacterium glutamicum

BACKGROUND: Pyruvate kinase (Pyk) catalyzes the generation of pyruvate and ATP in glycolysis and functions as a key switch in the regulation of carbon flux distribution. Both the substrates and products of Pyk are involved in the tricarboxylic acid cycle, anaplerosis and energy anabolism, which places Pyk at a primary metabolic intersection. Pyks are highly conserved in most bacteria and lower eukaryotes. Corynebacterium glutamicum is an industrial workhorse for the production of various amino acids and organic acids. Although C. glutamicum was assumed to possess only one Pyk (pyk1, NCgl2008), NCgl2809 was annotated as a pyruvate kinase with an unknown role. RESULTS: Here, we identified that NCgl2809 was a novel pyruvate kinase (pyk2) in C. glutamicum. Complementation of the WTΔpyk1Δpyk2 strain with the pyk2 gene restored its growth on d-ribose, which demonstrated that Pyk2 could substitute for Pyk1 in vivo. Pyk2 was co-dependent on Mn(2+) and K(+) and had a higher affinity for ADP than phosphoenolpyruvate (PEP). The catalytic activity of Pyk2 was allosterically regulated by fructose 1,6-bisphosphate (FBP) activation and ATP inhibition. Furthermore, pyk2 and ldhA, which encodes l-lactate dehydrogenase, were co-transcribed as a bicistronic mRNA under aerobic conditions and pyk2 deficiency had a slight effect on the intracellular activity of Pyk. However, the mRNA level of pyk2 in the wild-type strain under oxygen deprivation was 14.24-fold higher than that under aerobic conditions. Under oxygen deprivation, pyk1 or pyk2 deficiency decreased the generation of lactic acid, and the overexpression of either pyk1 or pyk2 increased the production of lactic acid as the activity of Pyk increased. Fed-batch fermentation of the pyk2-overexpressing WTΔpyk1 strain produced 60.27 ± 1.40 g/L of lactic acid, which was a 47% increase compared to the parent strain under oxygen deprivation. CONCLUSIONS: Pyk2 functioned as a pyruvate kinase and contributed to the increased level of Pyk activity under oxygen deprivation. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12896-016-0313-6) contains supplementary material, which is available to authorized users

Perceptions of Multi-Lateral Cross Boundary Organization of Local Governments in China: A Q-Analysis

Most public issues fall beyond the boundaries of any particular local government to solve. Conversely, many of those problems are equally likely to be too localized for national or state/provincial governments to solve. Rather, they scale to a level of governance somewhere between those two levels – often referred to as "the metropolitan region." Such scaling is a ubiquitous and global phenomenon, and governments in virtually every developed country have tried a variety of approaches to balance the desire for centralized coordination and decentralized application. For example, local governments in the United States have seen the emergence of regionally scaled voluntary cross-boundary organizations of local governments to address common public policy problems (Miller and Nelles, 2018; 2020). The issue of regional scaling in China has only recently attracted the attention of Chinese scholars and practitioners. As such, there is scant scholarly research even though China is experiencing steady growth in such organizational designs. The purpose of this thesis is to explore Chinese scholars' and practitioners' subjective understanding of the nature, purpose, and value of these new arrangements that scale to the level of "region." This research used Q-methodology to interview 54 Chinese government officials and scholars who have experience with working in cross-boundary organizations. The researcher used principal components analysis coupled with varimax rotation then generated four factors. These four factors identified illustrate different views toward these cross-boundary organizations in terms of how local government multi-lateral cross-boundary collaboration should be organized. This research has provided a new angle to view regional intergovernmental cooperation in China

Performance evaluation of Asphalt Rubber Gap-graded mixture

One of the most successful means of improving paving performance is by the use of Crump Rubber (CR). Increased demand for Asphalt Rubber Gap-graded (AR-Gap) mixtures as a pavement material has resulted from improvements in the basic asphalt binder as well as environmental advantages and improved performance in recent years. A number of agencies and researchers conducted AR-Gap mix studies to evaluate the design and performance of AR-Gap mixtures. In this study, the most recent research and practices in the design of AR-Gap mixtures were reviewed, and the performance characteristics of these mixtures were also summarized. In addition, the positive effect of adding ground rubber on the performance of the mixtures, including the effect on fatigue cracking, drainage, moisture susceptibility and permanent deformation is also reviewed. In conclusion, future aims in the building of AR-Gap pavement and performance potential were discussed, which will assist it in becoming a viable long-term pavement choice in the future. Based on the results of the evaluation process, it was discovered that there is still potential to improve the current design state of AR-Gap mixtures as well as the effect of rubber inserts in improving the performance of the mix

Consumption Risks in Option Returns

We offer evidence that exposures to consumption growth and consumption volatility are significantly priced in the cross-section of delta-hedged option returns. Consumption growth commands a positive risk premium, whereas consumption volatility commands a negative risk premium. Our results suggest that consumption risk exposures provide rational foundations for well-known relations between options moneyness or idiosyncratic underlying-stock volatility and the cross-section of delta-hedged option returns. Furthermore, those risk premiums can also price stocks. In a representative-agent economy with recursive preferences, our results suggest that investors prefer early resolution of uncertainty

A Simple Asymmetric Momentum Make SGD Greatest Again

We propose the simplest SGD enhanced method ever, Loss-Controlled Asymmetric Momentum(LCAM), aimed directly at the Saddle Point problem. Compared to the traditional SGD with Momentum, there's no increase in computational demand, yet it outperforms all current optimizers. We use the concepts of weight conjugation and traction effect to explain this phenomenon. We designed experiments to rapidly reduce the learning rate at specified epochs to trap parameters more easily at saddle points. We selected WRN28-10 as the test network and chose cifar10 and cifar100 as test datasets, an identical group to the original paper of WRN and Cosine Annealing Scheduling(CAS). We compared the ability to bypass saddle points of Asymmetric Momentum with different priorities. Finally, using WRN28-10 on Cifar100, we achieved a peak average test accuracy of 80.78\% around 120 epoch. For comparison, the original WRN paper reported 80.75\%, while CAS was at 80.42\%, all at 200 epoch. This means that while potentially increasing accuracy, we use nearly half convergence time. Our demonstration code is available at\\ https://github.com/hakumaicc/Asymmetric-Momentum-LCA

Analysis of a stochastic delay competition system driven by Lévy noise under regime switching

This paper is concerned with a stochastic delay competition system driven by Lévy noise under regime switching. Both the existence and uniqueness of the global positive solution are examined. By comparison theorem, sufficient conditions for extinction and non-persistence in the mean are obtained. Some discussions are made to demonstrate that the different environment factors have significant impacts on extinction. Furthermore, we show that the global positive solution is stochastically ultimate boundedness under some conditions, and an important asymptotic property of system is given. In the end, numerical simulations are carried out to illustrate our main results