Enhancing the biosynthesis of nicotinamide mononucleotide in Lactococcus lactis by heterologous expression of FtnadE.

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.

[Spatiotemporal dynamics and related affecting factors of summer algal blooms in Xiangxi Bay of Three Gorges Reservoir].

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.