Background Fluorinases play a unique role in the production of fluorine-containing organic molecules by biological methods. Whole-cell catalysis is a better choice in the large-scale fermentation processes, and over 60% of industrial biocatalysis uses this method. However, the in vivo catalytic efficiency of fluorinases is stuck with the mass transfer of the substrates. Results A gene sequence encoding a protein with fluorinase function was fused to the N-terminal of ice nucleation protein, and the fused fluorinase was expressed in Escherichia coli BL21(DE3) cells. SDS-PAGE and immunofluorescence microscopy were used to demonstrate the surface localization of the fusion protein. The fluorinase displayed on the surface showed good stability while retaining the catalytic activity. The engineered E.coli with surface-displayed fluorinase could be cultured to obtain a larger cell density, which was beneficial for industrial application. And 55% yield of 5′-fluorodeoxyadenosine (5′-FDA) from S-adenosyl-L-methionine (SAM) was achieved by using the whole-cell catalyst. Conclusions Here, we created the fluorinase-containing surface display system on E.coli cells for the first time. The fluorinase was successfully displayed on the surface of E.coli and maintained its catalytic activity. The surface display provides a new solution for the industrial application of biological fluorination. Graphical Abstract

Xylose is the raw material for the synthesis of many important platform compounds. At present, xylose is commercially produced by chemical extraction. However, there are still some bottlenecks in the extraction of xylose, including complicated operation processes and the chemical substances introduced, leading to the high cost of xylose and of synthesizing the downstream compounds of xylose. The current market price of xylose is 8× that of glucose, so using low-cost glucose as the substrate to produce the downstream compounds of xylose can theoretically reduce the cost by 70%. Here, we designed a pathway for the biosynthesis of xylose from glucose in Escherichia coli. This biosynthetic pathway was achieved by overexpressing five genes, namely, zwf, pgl, gnd, rpe, and xylA, while replacing the native xylulose kinase gene xylB with araL from B. subtilis, which displays phosphatase activity toward D-xylulose 5-phosphate. The yield of xylose was increased to 3.3 g/L by optimizing the metabolic pathway. Furthermore, xylitol was successfully synthesized by introducing the xyl1 gene, which suggested that the biosynthetic pathway of xylose from glucose is universally applicable for the synthesis of xylose downstream compounds. This is the first study to synthesize xylose and its downstream compounds by using glucose as a substrate, which not only reduces the cost of raw materials, but also alleviates carbon catabolite repression (CCR), providing a new idea for the synthesis of downstream compounds of xylose.

Quantum dots (QDs) are widely used in sensors, photovoltaic cells, and other fields due to their unique structural and optical properties. Physical and chemical methods that are commonly used for the synthesis of QDs require high-temperature and high-pressure environments, as well as toxic reagents. Biosynthesis overcomes these limitations and offers a novel method for producing QDs that is both cost-effective and environmentally friendly. Mercaptan substances in organisms play a key role in the synthesis of QDs, such as glutathione (GSH) and plant chelating peptides. However, the preparation of QDs using metallothionein (MT) has rarely been reported, and the synthesis mechanism is lacking. In this paper, we describe the in vivo biosynthesis of CdSe QDs by recombinant Escherichia coli expressing metallothionein, which has a synthetic advantage compared to the original strain. The fluorescence emission spectrum of the synthesized QDs was located at 550 nm with a Stokes shift of 140 nm, and the yield of the biological QDs was calculated to be 2.91%. Furthermore, the role of metallothionein in the synthesis of QDs was tentatively validated. The initial nucleus of the QDs is proposed to be originating from the Cys-Cd, followed by the subsequent introduction of the HSe– group, and its coordination with Cd2+ promotes layer-by-layer growth. Here, we established a green, mild, and efficient in vivo synthesis pathway for QDs, providing more possibilities for the synthesis of biological QDs in the future.