The opal-like SiO 2 microcarriers with different pore diameters named opal-SiO 2 I and opal-SiO 2 II were synthesized and utilized as microcarriers to immobilize Rhizopus oryzae lipase (ROL) and Aspergillus oryzae α-amylases (AOA). ROL and AOA can be more stably immobilized on the cross-linked SiO 2 opals by neopentyl glycol diglycidyl ether (NGDE), which is the first attempt to use it as a cross-linking agent compared with glutaraldehyde. According to the morphology analysis, multiple layers of SiO 2 monodisperse microspheres were regularly packed and formed an opal-like structure, and enzymes were well scattered and immobilized throughout the SiO 2 opals. The results showed that the performance of enzymes immobilized on opal-SiO 2 II with a larger specific surface area was much better than that of opal-SiO 2 I.
Serotonin is a neurotransmitter that plays an essential
regulatory
role in numerous cognitive and behavioral functions. Recent advances
in synthetic biology have enabled engineering of non-natural biosynthetic
pathways for serotonin production in E. coli. Here, an optimized heterologous serotonin biosynthetic pathway
was engineered in E. coli and coupled with the
biosynthetic and regeneration modules of the endogenous vital cofactor
tetrahydrobiopterin (BH4) for efficient serotonin production using
whole-cell catalysis. Further metabolic engineering efforts were performed
to ensure an adequate endogenous BH4 supply, including enhancements
of GTP biosynthesis and intracellular reducing power availability.
Using the optimized fed-batch fermentation, an overall maximum serotonin
yield of 40.3% (mol/mol) and a peak titer of 1.68 g/L (production
rate of 0.016 g/L/h) were achieved. The strategies employed in this
study show the promise of using E. coli for
pterin self-sufficiency and high-level serotonin production, and the
engineered strains hold the potential for use in industrial applications.
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