Self-regulated efficient production of L-threonine via an artificial quorum sensing system in engineered Escherichia coli.

Imbalance in carbon flux distribution is one of the most important factors affecting the further increase in the yield of high value-added natural products in microbial metabolic engineering. Meanwhile, the most common inducible expression systems are difficult to achieve industrial-scale production due to the addition of high-cost or toxic inducers during the fermentation process. Quorum sensing system, as a typical model for density-dependent induction of gene expression, has been widely applied in synthetic biology. However, there are currently few reports for efficient production of microbial natural products by using quorum sensing system to self-regulate carbon flux distribution. Here, we designed an artificial quorum sensing system to achieve efficient production of L-threonine in engineered Escherichia coli by altering the carbon flux distribution of the central metabolic pathways at specific periods. Under the combination of switch module and production module, the system was applied to divide the microbial fermentation process into two stages including growth and production, and improve the production of L-threonine by self-inducing the expression of pyruvate carboxylase and threonine extracellular transporter protease after a sufficient amount of cell growth. The final strain TWF106/pST1011, pST1042pr could produce 118.2 g/L L-threonine with a yield of 0.57 g/g glucose and a productivity of 2.46 g/(L· h). The establishment of this system has important guidance and application value for the production of other high value-added chemicals in microorganisms by self-regulation.

Highly Sensitive Colorimetric Detection of a Variety of Analytes via the Tyndall Effect.

This work initially reports the use of a quite familiar optical phenomenon of colloidal solutions, namely, the Tyndall Effect (TE) as signal readout for highly sensitive colorimetric chemical and biological analysis. Taking gold nanoparticles (GNPs) as a model colloid, the TE-inspired assay (TEA) is developed based on the conversion of a specific recognition event (e.g., the aptamer-analyte binding) into the aggregation of GNPs, leading to a significant TE enhancement. In the TEA, a cheap laser pointer pen is used as a hand-held light source, while a smartphone serves as a portable quantitative reader. The results show that the TE signaling strategy achieves a ∼1000-fold sensitivity improvement compared with the most common surface plasmon resonance signaling method using GNPs. The utility of the TEA is well demonstrated with the inexpensive, rapid, and portable detection of trace levels of analytes ranging from an important small-molecule drug (cocaine, ∼1.5 pM detection limit) to a protein biomarker (interferon-γ, ∼2.2 fM detection limit) and a toxic metal ion (Ag+, ∼1.4 nM detection limit). In addition, as the TE enhancement simply stems from the aggregation of either bare (unmodified) or modified GNPs, the TEA is universally applicable to almost all of the existing GNP-based liquid-phase colorimetric assays. The TEA method developed herein lights a new way for equipment-free point-of-care analysis in various fields including medical diagnosis, food safety evaluation, and environmental monitoring, especially in the resource-poor areas of the world.

Uricase-containing coacervate microdroplets as enzyme active membrane-free protocells for detoxification of uric acid in serum.

Based on the unique property of preferential sequestration of guest molecules, coacervate microdroplets are proposed as enzyme active membrane-free protocells, in which uricase is loaded for efficient detoxification of uric acid in serum.