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.

Fatty acid composition has an important influence on the fluidity of biological membranes, which is a key factor for the survival of Escherichia coli. With the aim to modify fatty acid composition in this experimentally friendly microorganism, the AtFab2 gene, encoding the Arabidopsis thaliana fatty acid desaturase, was expressed separately and jointly with AtFatA, a fatty acid thioesterase of the same plant origin. The expression of ATFab2 desaturase resulted in an enhancement of cis-vaccenic acid (18:1Δ11) contents, while amounts of palmitioleic acid (16:1Δ9) accumulated by E. coli were increased by 130% for the expression of the AtFatA thioesterase. In the final engineered strain co-expressing AtFab2 and AtFatA, the percentage of palmitic acid (16:0), the most abundant saturated fatty acid found in E. coli, was reduced to 29.9% and the ratio of unsaturated fatty acid to saturated fatty acid reached 2:1. Free fatty acids accounted for about 40% of total fatty acid profiles in the recombinant strain expressing both two genes, and the unsaturated fatty acid contents reached nearly 75% in the free fatty acid profiles. The increase of unsaturated fatty acid level might provide some implication for the construction of cold tolerant strains.