Bayesian Modal Regression based on Mixture Distributions

Compared to mean regression and quantile regression, the literature on modal regression is very sparse. We propose a unified framework for Bayesian modal regression based on a family of unimodal distributions indexed by the mode along with other parameters that allow for flexible shapes and tail behaviors. Following prior elicitation, we carry out regression analysis of simulated data and datasets from several real-life applications. Besides drawing inference for covariate effects that are easy to interpret, we consider prediction and model selection under the proposed Bayesian modal regression framework. Evidence from these analyses suggest that the proposed inference procedures are very robust to outliers, enabling one to discover interesting covariate effects missed by mean or median regression, and to construct much tighter prediction intervals than those from mean or median regression. Computer programs for implementing the proposed Bayesian modal regression are available at https://github.com/rh8liuqy/Bayesian_modal_regression.Comment: 34 pages, 14 figure

Fabrication of porous Al2O3-based ceramics using combustion synthesized powders

Porous Al2O3-based ceramics were fabricated from powders synthesized via a solution combustion process using starch and urea as fuels. Effects of the relative fuel-to-oxidant ratio (φe = 1.4, 1.6, 1.8 and 2.0, respectively) on open porosity, pore size distribution and flexural strength of the as-prepared porous Al2O3-based ceramics were investigated. Experimental results revealed that the densification ability of the as-synthesized powders increased significantly as φe increased, and open porosity, pore size distribution and flexural strength of the porous ceramics exhibited remarkable dependence on the densification ability of the powders instead of the weight fraction of the charred organic residuals in the powders. SEM micrographs disclosed that the porous ceramics from the precursors with φe = 1.8 or 2.0 exhibited significantly homogenous microstructures including pore size and pore distribution

Annexin A7 and Its Related Protein Suppressor of Death Domains Regulates Migration and Proliferation of Hca-P Cells

Objective: This study was to investigate whether annexin A7 (AnnexinA7, ANXA7) and its co-related protein tumor celldeath domain silencer [suppressor of death domains (SODD)] regulates the migratory phenotype of liver cancer cells.Materials and Methods: In this experimental study, expression of ANXA7 in Hca-P cells, PANXA7 downregulatedcells and PANXA7 unrelated sequence cells was detected by real-time quantitative polymerase chainreaction (PCR) at mRNA level and western blotting at protein level. Transwell migration and invasion assayswere performed to determine the migratory phenotype.Results: After inhibition of ANXA7 expression, expression of SODD protein was also significantly decreased (P<0.05).Transwell cell transfer experiments showed that number of tumor cells that penetrated into the cell membrane wassignificantly reduced after ANXA7 silencing (P<0.05). Transwell cell invasion assay showed that number of tumorcells penetrating into Matrigel was significantly reduced after ANXA7 down-regulation (P<0.05). The CCK8 assay wasmeasured at 0, 24 and 48 hours, and proliferation rate of PANXA7 lower weir cells was slower than that of Hca-P cellsand PANXA7 non-related sequence cells (P<0.05).Conclusion: SODD expression was decreased with the down-regulation of ANXA7. Down-regulating ANXA7 in Hca-Pcells decreased proliferation, migration and invasion of tumor cells

Removing the by-products acetic acid and NH4+ from the l-tryptophan broth by vacuum thin film evaporation during l-tryptophan production

Background: During l-tryptophan production by Escherichia coli, the by-products, acetic acid and NH4+, accumulate in the fermentation broth, resulting in inhibited cell growth and activity and decreased l-tryptophan production. To improve the l-tryptophan yield and glucose conversion rate, acetic acid and NH4+ were removed under low-temperature vacuum conditions by vacuum scraper concentrator evaporation; the fermentation broth after evaporation was pressed into another fermenter to continue fermentation. To increase the volatilisation rate of acetic acid and NH4+ and reduce damage to bacteria during evaporation, different vacuum evaporation conditions were studied. Results: The optimum operating conditions were as follows: vacuum degree, 720 mm Hg; concentration ratio, 10%; temperature, 60°C; and feeding rate, 300 mL/min. The biomass yield of the control fermentation (CF) and fermentation by vacuum evaporation (VEF) broths was 55.1 g/L and 58.3 g/L at 38 h, respectively, (an increase of 5.8%); the living biomass yield increased from 8.9 (CF) to 10.2 pF (VEF; an increase of 14.6%). l-tryptophan production increased from 50.2 g/L (CF) to 60.2 g/L (VEF) (an increase of 19.9%), and glucose conversion increased from 18.2% (CF) to 19.5% (VEF; an increase of 7.1%). The acetic acid concentrations were 2.74 g/L and 6.70 g/L, and the NH4+ concentrations were 85.3 mmol/L and 130.9 mmol/L in VEF and CF broths, respectively. Conclusions: The acetic acid and NH4+ in the fermentation broth were quickly removed using the vacuum scraper concentrator, which reduced bacterial inhibition, enhanced bacterial activity, and improved the production of l-tryptophan and glucose conversion rate.How to cite: Xu Q, Bai F, Chen N, et al. Removing the by-products acetic acid and NH4+ from the l-tryptophan broth by vacuum thin film evaporation during l-tryptophan production. Electron J Biotechnol 2018; 33. https://doi.org/10.1016/j.ejbt.2018.04.003. Keywords: Acetic acid, Amino acid, Concentration, Escherichia coli, Fermentation, Glucose conversion rate, l-tryptophan production, NH4+, Vacuum thin film evaporation, Waste produc

Gene modification of the acetate biosynthesis pathway in Escherichia coli and implementation of the cell recycling technology to increase L-tryptophan production.

The implementation of a novel cell recycling technology based on a special disk centrifuge during microbial fermentation process can continuously separate the product and harmful intermediates, while maintaining the cell viability owing to the installed cooling system. Acetate accumulation is an often encountered problem in L-tryptophan fermentation by Escherichia coli. To extend our previous studies, the current study deleted the key genes underlying acetate biosynthesis to improve l-tryptophan production. The deletion of the phosphotransacetylase (pta)-acetate kinase (ackA) pathway in a gltB (encoding glutamate synthase) mutant of E. coli TRTHB, led to the highest production of l-tryptophan (47.18 g/L) and glucose conversion rate (17.83%), with a marked reduction in acetate accumulation (1.22 g/L). This strain, TRTHBPA, was then used to investigate the effects of the cell recycling process on L-tryptophan fermentation. Four different strategies were developed concerning two issues, the volume ratio of the concentrated cell solution and clear solution and the cell recycling period. With strategy I (concentrated cell solution: clear solution, 1: 1; cell recycling within 24-30 h), L-tryptophan production and the glucose conversion rate increased to 55.12 g/L and 19.75%, respectively, 17.55% and 10.77% higher than those without the cell recycling. In addition, the biomass increased by 13.52% and the fermentation period was shortened from 40 h to 32 h. These results indicated that the cell recycling technology significantly improved L-tryptophan production by E. coli

The linear relation of cell and tryptophan biosynthesis during cell recycling period (20–26 h) with strategy I and III.

<p>The linear relation of cell and tryptophan biosynthesis during cell recycling period (20–26 h) with strategy I and III.</p

Effect of modifying the genes required for acetate synthesis on biomass and production of L-tryptophan in L-tryptophan fermentation (<i>P</i><0.05).

<p>Effect of modifying the genes required for acetate synthesis on biomass and production of L-tryptophan in L-tryptophan fermentation (<i>P</i><0.05).</p

Analysis of process parameters in L-tryptophan production by using the strain TRTHB (<i>P</i><0.05).

<p>Analysis of process parameters in L-tryptophan production by using the strain TRTHB (<i>P</i><0.05).</p

Comparisons of biomass (a), L-tryptophan production and fermentation period (b) in L-tryptophan fermentation by TRTHBPA between strategy I and the control (without cell recycling).

<p>Comparisons of biomass (a), L-tryptophan production and fermentation period (b) in L-tryptophan fermentation by TRTHBPA between strategy I and the control (without cell recycling).</p

Strains, plasmids, and primers used in this study.

<p>Strains, plasmids, and primers used in this study.</p