Search

BACKGROUND: Nicotinamide mononucleotide (NMN), a key intermediate of nicotinamide adenine dinucleotide, plays an important in anti‐aging and disease. Lactococcus lactis, an important probiotic lactic acid bacteria (LAB), has shown great potential for the biosynthesis of NMN, which will significantly affect the probiotic effects of the dairy products. RESULTS: We used the CRISPR/nCas9 technique to knockout nadR gene of L. lactis NZ9000 to enhance the accumulation of NMN by 61%. The nadE* gene from Francisella tularensis with codon optimization was heterologous in L. lactis NZ9000ΔnadR and has a positive effect on NMN production. Combined with optimization of the concentration of substrate nicotinamide, a final intracellular NMN titer was 2289 μmol L–1 mg–1 with 10 g L–1 nicotinamide supplement, which was 5.7‐fold higher than that of the control. The transcription levels of key genes (pncA, nadD and prs1) involved in NMN biosynthesis were up‐regulated by more than two‐fold, indicating that the increase of NMN titer was attributed to FtnadE* heterologous expression. CONCLUSION: Our study provides a better understanding of the NMN biosynthesis pathway in L. lactis, and can facilitate NMN production in LAB via synthetic biology approaches. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Determining the development of artificial frozen walls by present methods is challenging where substantial seepage occurs because fixed monitoring points only indicate physical properties in small areas. Here we use ultrasonic acoustic methods to determine the physical properties between two freezing pipes during freezing. Sensitivity analysis indicates that wave velocity is sensitive to physical properties, and the sensitivity rank is water content > temperature > density. The attenuation coefficient has a low sensitivity to physical parameters, whereas dominant frequency is sensitive to temperature and water content but insensitive to density. Wave velocity increases with temperature and density in a quadratic relationship, and with water content in a linear relationship. Dominant frequency increases with temperature and water content in a quadratic relationship. A multiple regression model of wave velocity and dominant frequency established by stepwise regression can be used to predict the relationship between wave velocity and temperature of frozen fine sand in different areas where the soil properties are similar to those reported here. Wave velocity and dominant frequency measured in the laboratory can be used to predict the relationship between acoustic parameters and temperature in field conditions after curve move based on the first data point from field measurements. The procedure of curve moving involves calculating the difference in value of the first data point between laboratory and field measurements at the same temperature level, and then moving the predicted curve of the laboratory test upward or downward according to the difference. Supplementary material: Experimental datasets are available at https://doi.org/10.6084/m9.figshare.12268970 [ABSTRACT FROM AUTHOR]

In June - August 2008, the cyanobacterial bloom and chlorophycean bloom broke out one after the other in the Xiangxi Bay of Three Gorges Reservoir. Based on the weekly monitoring in summer in the Bay, and by using cluster analysis and discriminant analysis, the spatiotemporal dynamics and related affecting factors of the two blooms were studied. Each of the blooms could be divided into non-bloom group, transitional group, and bloom group. The two blooms had different uptake levels of dissolved Si (DSi), NO3--N + NO2--N, and PO43--P. Cyanobacterial bloom had lower DSi concentration and lower TN/TP, DSi/TN and DSi/TP ratios than chlorophycean bloom. The discriminant factors of cyanobacterial bloom were Chl a, TN and PO43--P, while those of chlorophycean bloom were Chl a and DSi. Better discriminant results were obtained when dividing each bloom into non-bloom group and bloom group. The critical value of Chl a for cyanobacterial bloom and chlorophycean bloom was 40 and 20 μg × L-1, respectively. [ABSTRACT FROM AUTHOR]

In June - August 2008, the cyanobacterial bloom and chlorophycean bloom broke out one after the other in the Xiangxi Bay of Three Gorges Reservoir. Based on the weekly monitoring in summer in the Bay, and by using cluster analysis and discriminant analysis, the spatiotemporal dynamics and related affecting factors of the two blooms were studied. Each of the blooms could be divided into non-bloom group, transitional group, and bloom group. The two blooms had different uptake levels of dissolved Si (DSi), NO3(-)-N + NO2(-)-N, and PO4(3-)-P. Cyanobacterial bloom had lower DSi concentration and lower TN/TP, DSi/TN and DSi/TP ratios than chlorophycean bloom. The discriminant factors of cyanobacterial bloom were Chl a, TN and PO4(3-)-P, while those of chlorophycean bloom were Chl a and DSi. Better discriminant results were obtained when dividing each bloom into non-bloom group and bloom group. The critical value of Chl a for cyanobacterial bloom and chlorophycean bloom was 40 and 20 microg x L(-1), respectively.