Tetrahydrobiopterin self-sufficiency and serotonin production in Escherichia coli
Because of public concern over the rise in depression, serotonin has gained attention as a feel-good messenger. It is an inhibitory neurotransmitter that has many clinical and pharmaceutical applications, such as regulating mood, managing behavior, maintaining sleep cycles, and scavenging harmful free radicals in the body. It affects almost every aspect of brain activity: from regulating mood, energy, and memory to shaping outlook on life. The antidepressant fluoxetine hydrochloride, for example, works by increasing serotonin levels in the brain.
Serotonin can be obtained in vitro from its precursor 5-hydroxytryptophan (5-HTP) through a one-step conversion. The main source of 5-HTP depends on plant tissue extraction. At present, the seeds of Ghanaian cereals are known to contain high levels of 5-HTP, so the plant is a major source of 5-HTP on the market. However, the geographical limitations of cultivation and the lack of raw materials have severely affected the industrial production of 5-HTP, which in turn affects the yield of serotonin obtained by this method. With the rapid development of modern synthetic biology in recent years, the use of metabolically engineered Escherichia coli as a cell factory to produce serotonin has been gradually practiced by many researchers.
A research team in China synthesized serotonin de novo using glucose or glycerol as a carbon source, or through whole-cell catalytic means, using L-tryptophan as substrate by hydroxylation and decarboxylation. The team first optimized two key enzymes in the heterologous serotonin synthesis pathway, tryptophan hydroxylase, and decarboxylase, then introduced the BH4 biosynthesis and regeneration modules into the E. coli genome and, through further metabolic engineering. These include enhancing the biosynthesis of the BH4 precursor GTP and increasing the intracellular availability of the reducing cofactor NADH/NADPH to ensure adequate endogenous BH4 supply. The optimal fed-batch fermentation was used to achieve 40.3% (mol/mol) overall maximum serotonin production and 1.68g/L peak titer (0.016g/L/h). The strategy employed in this study showed the promise of using E. coli for tetrahydrobiopterin self-sufficiency and high levels of serotonin production, demonstrating the potential of engineered strains for industrial applications.
The development of synthetic biology technology opens up new ways of realization and application in the bioenergy field
In the field of bioenergy, the comprehensive utilization of lignocellulose has received a lot of attention. Lignocellulose is the most abundant organic matter in nature. Bioconversion of lignocellulose with biotechnology as the core has become one of the key technologies in bioenergy development, biomass resource processing, and the green chemical industry. Related research has also become a hot but difficult point in the current industrial microbial technology.
As a sustainable form of energy, bioenergy is the most promising alternative to traditional energy, can be developed on a large scale, is conducive to protecting the environment and solving the energy crisis, and can also promote the development of other emerging bioenergy industries. Bioenergy mainly includes biodiesel, bioethanol, and biohydrogen production.
- Biodiesel
Biodiesel is high-fatty acid methane derived from bioenergy resources such as aquatic plants, oil crops, and animal fats by biochemical means, which can be used as a substitute for conventional diesel. Compared with traditional diesel oil, biodiesel has the characteristics of strong knock resistance, high cetane number, excellent ignition, good mobility, and high safety, and does not contain carcinogenic harmful components such as aromatic hydrocarbons. The energy consumption of biodiesel accounts for 25% of that of traditional diesel. It is high-quality green energy, and its biodegradation rate is as high as 98%, which is twice that of traditional diesel. Synthetic biology strategies are currently used to enable oleaginogenic microorganisms such as yeast and E. coli to produce biodiesel without the use of plant and animal oils. - Bioethanol
Bioethanol can be used to improve the quality of the oil. It comes from plants and is the processing product of alcohol. The existing oil amendments mainly include methyl tert-butyl ether, bioethanol, and ethyl tert-butyl ether. Bioethanol amendments have been popularized and used in some countries, and have achieved remarkable results. At present, remarkable progress has been made in enhancing the production of bioethanol from Saccharomyces cerevisiae with synthetic biology technology, which has a remarkable driving effect on the industrialization of agriculture. - Biological hydrogen production
Biological hydrogen production is hydrogen produced by anaerobic bacteria or photosynthetic bacteria using carbohydrate hydrogen donors. Biological hydrogen production is made from processing wastewater of sugar, starch, soybean, winemaking, and wheat dairy products, as well as agricultural wastes such as bran, residue, and straw. Biological hydrogen production can not only meet the needs of production and daily life of hydrogen sources but also realize the recycling of waste. Hydrogen-producing bacteria can produce hydrogen from biomass under anaerobic or aerobic conditions through synthetic biological modification. Some companies such as Boeing are focusing on and investing in the field of biological hydrogen production.
Conclusion
Biomass-fueled cogeneration is, of course, still achieved by direct combustion of lignocellulose. However, for biodiesel and fuel ethanol, the cost and capacity would be greatly increased if the supply chain could fully utilize the huge stock of lignocellulose. But the difficulty of biological energy effective utilization of lignocellulose still lies in the degradation of lignin separation and low-cost treatment and comprehensive utilization, if can completely solve these problems, will greatly through the use of biofuels supply chain, and the development of synthetic biology technology realization and application for bio-energy field opens up a new way.
