BackgroundSuccinic acid is a valuable product due to its wide-ranging utilities. To improve succinate production and reduce by-products formation, Escherichia coli NZN111 was constructed by insertional inactivation of lactate dehydrogenase (LDH) and pyruvate formate lyase (PFL) encoded by the genes ldhA and pflB, respectively. However, this double-deletion mutant is incapable of anaerobically growing on glucose in rich or minimal medium even with acetate supplementation. A widespread hold view is that the inactivation of NADH-dependent LDH limits the regeneration of NAD+ and consequently disables proper growth under anaerobic conditions.ResultsIn this study, genome-scale metabolic core model of E. coli was reconstructed and employed to perform all simulations in silico according to the reconstruction of engineered strain E. coli NZN111. Non-optimized artificial centering hit-and-run (ACHR) method and metabolite flux-sum analysis were utilized to evaluate metabolic characteristics of strains. Thus, metabolic characteristics of the strains wild-type E. coli, ldhA mutant, pflB mutant, and NZN111 under anaerobic conditions were successfully unraveled.Conclusions We found a viewpoint contrary to the widespread realization that an NADH/NAD+ in NZN111 mainly resulted from the inactivation of PFL rather than the inactivation of LDH. In addition, the two alternative anaerobic fermentation pathways, lactate and ethanol production pathways, were blocked owing to the disruption of ldhA and pflB, resulting in insufficient NAD+ regeneration to oxidize or metabolize glucose for cell growth. Furthermore, we speculated reaction NADH16, the conversion of ubiquinone-8 (q8) to ubiquinol-8 (q8h2), as a potential amplification target for anaerobically improving cell growth and succinate production in NZN111.Electronic supplementary materialThe online version of this article (doi:10.1186/s40643-016-0125-5) contains supplementary material, which is available to authorized users.

Reconstruction and application of genome-scale metabolic models (GEMs) have facilitated metabolic engineering by providing a platform on which systematic computational analysis of metabolic networks can be performed. In this study, a GEM of Escherichia coli NZN111 was employed by the analysis of production and growth coupling (APGC) algorithm to identify genetic strategies for the overproduction of succinate. Through in silico simulation and reaction expression analysis, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), phosphoglycerate kinase (PGK), triosephosphate isomerase (TPI), and phosphoenolpyruvate carboxylase (PPC), encoded by gapA, pgk, tpiA, and ppc, respectively, were selected for experimental overexpression. The results showed that overexpressing any of these could improve both growth and succinate production. Specifically, overexpression of GAPDH or PGK showed a significant effect with up to 24% increase in succinate production. These results indicate that the APGC algorithm can be effectively used to guide genetic manipulation for strain design by identifying genome-wide gene amplification targets.

The platform vibration will cause spectral images blurring when using computed tomographic imaging spectrometer (CTIS) on unstable platform, especially in space-borne or ship-based application. As a result, a phenomenon of blur-induced spectral distortion occurs, which greatly affects the accuracy of classification of target. However, without easy accessibility of the knowledge of image motion kernel, it is difficult to restore the degraded images accurately. With the desire to solve the motion function, this paper has made a breakthrough by proposing a motion detection method using short exposure images from zeroth order beam light of 2D-grating. Contributed by the accurate motion kernel, blurred spectral images could be reliably restored as well as the improvement of spectra accuracy. Laboratory experiment result shows the robust spectra restoration capability of this technique.

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Objective To investigate the relationship between inflammation and autophagy in high-fat obese rats by applying three intervention methods (aerobic exercise/orlistat/food restriction). Methods Male SD rats were randomly divided into normal control group (NC group, n = 10) and high fat model group (HC group, n = 67). 40 rats (n = 58) were randomly divided into high fat control group (HC group, n = 10), high fat exercise group (HE group, n = 10), high fat orlistat group (HO group, n = 10), high fat diet group (HR group, n = 10). After 8 weeks, the weight and body length of rats were measured, and Lee's index and body fat ratio were calculated; Four blood lipids in rat serum were detected by Elisa method. Inflammatory factors IL-6 and TNF-α in testicular tissue were detected by Elisa method. The expression levels of autophagic protein AKT and mTOR mRNA in testis were detected by RT-PCR. Results (1) Compared with NC group, the body weight and Lee's index of rats in HC group increased significantly (P < 0.01), and the body fat ratio increased significantly (P < 0.05); The body weight in HR group was significantly lower than that in HE and HO groups (P < 0.01). (2) Compared with NC group, the levels of TC, TG and LDL-C in serum of HC group increased significantly(P < 0.01), while the level of HDL-C decreased significantly(P < 0.01); Compared with HC group, the levels of TC and TG in HR and HE groups decreased significantly(P < 0.01), while the level of HDL-C in HR group increased significantly(P < 0.01). (3) The level of IL-6 in testicular tissue of HC group was significantly higher than that of NC group(P < 0.01). Compared with HC group, the level of IL-6 in HE and HR groups decreased significantly(P < 0.01), and the level of TNF-α in HR group decreased significantly(P < 0.05). (4) The expression level of AKT mRNA in testicular tissue of HC group was significantly higher than that of NC group(P < 0.05). Compared with HC, the expression level of each index in HO and HR groups was significantly increased(P < 0.01), and the AKT mRNA level in HE group was significantly higher than that in HC group(P < 0.05). Conclusions (1) The obese rat model reproduced in this study is successful. The three intervention methods can inhibit the weight growth of rats and effectively improve the dyslipidemia, of which the effect of food restriction intervention is the most significant. (2) The three intervention methods can effectively alleviate the inflammatory level in the testis of obese rats; The effect of aerobic exercise and food restriction intervention on reducing the level of inflammation is better than that of orlistat drug intervention. (3) Compared with food restriction intervention, exercise intervention has a greater impact on AKT and mTOR mRNA expression levels. The level of inflammatory factors is negatively correlated with the expression of autophagy related proteins, and autophagy level has a high degree of tissue specificity.