Beet molasses-based feeding strategy enhances recombinant thermostable glucose isomerase production byEscherichia coliBL21 (DE3)

Sustainable production of a biotechnologically relevant β-galactosidase in Escherichia coli cells using crude glycerol and cheese whey permeate

Responsible use of natural resources and waste reduction are key concepts in bioeconomy. This study demonstrates that agro-food derived-biomasses from the Italian food industry, such as crude glycerol and cheese whey permeate (CWP), can be combined in a high-density fed-batch culture to produce a recombinant β-galactosidase from Marinomonas sp. ef1 (M-βGal). In a small-scale process (1.5 L) using 250 mL of crude glycerol and 300 mL of lactose-rich CWP, approximately 2000 kU of recombinant M-βGal were successfully produced along with 30 g of galactose accumulated in the culture medium. The purified M-βGal exhibited high hydrolysis efficiency in lactose-rich matrices, with hydrolysis yields of 82 % in skimmed milk at 4 °C and 94 % in CWP at 50 °C, highlighting its biotechnological potential. This approach demonstrates the effective use of crude glycerol and CWP in sustainable and cost-effective high-density Escherichia coli cultures, potentially applicable to recombinant production of various proteins.

Rational engineering of the Trichoderma reesei RUT-C30 strain into an industrially relevant platform for cellulase production

BACKGROUND

The path for the development of hypersecreting strains of Trichoderma reesei capable of producing industrially relevant enzyme titers remains elusive despite over 70 years of research and industrial utilization. Herein, we describe the rational engineering of the publicly available T. reesei RUT-C30 strain and a customized process for cellulase production based on agroindustrial by-products.

RESULTS

A CRISPR/Cas9 system was used to introduce six genetic modifications in RUT-C30. Implemented changes included the constitutive expression of a mutated allele of the cellulase master regulator XYR1, the expression of two heterologous enzymes, the β-glucosidase CEL3A from Talaromyces emersonii and the invertase SUC1 from Aspergillus niger, and the deletion of genes encoding the cellulase repressor ACE1 and the extracellular proteases SLP1 and PEP1. These alterations resulted in a remarkable increase of protein secretion rates by RUT-C30 and amended its well described β-glucosidase deficiency while enabling the utilization of sucrose and eliminating the requirement of inducing sugars for enzyme production. With a developed sugarcane molasses-based bioprocess, the engineered strain reached an extracellular protein titer of 80.6 g L^-1 (0.24 g L^-1 h^-1), which is the highest experimentally supported titer so far reported for T. reesei. The produced enzyme cocktail displayed increased levels of cellulase and hemicellulase activities, with particularly large increments being observed for the specific activities of β-glucosidase (72-fold) and xylanase (42-fold). Notably, it also exhibited a saccharification efficiency similar to that of a commercially available cellulase preparation in the deconstruction of industrially pretreated sugarcane straw.

CONCLUSION

This work demonstrates the rational steps for the development of a cellulase hyperproducing strain from a well-characterized genetic background available in the public domain, the RUT-C30, associated with an industrially relevant bioprocess, paving new perspectives for Trichoderma research on cellulase production.

High-level expression of Thermobifida fusca glucose isomerase for high fructose corn syrup biosynthesis

Glucose isomerase (GIase), an efficient enzyme in the isomerization of d-glucose to d-fructose, has been widely used in food processing. In this study, an efficient expression system for a Thermobifida fusca GIase (GIase_Tfus) in Escherichia coli was firstly designed via a two-stage feeding strategy for improving expression level. The cultivation strategy was performed at an exponential feeding rate during the pre-induction phase, followed by a gradient-decreasing feeding rate at the induction phase in a 3-L fermenter. During this process, the effect of induction conditions and the complex nitrogen supplementation in feeding solutions on GIase_Tfus production were investigated and optimized. Under the optimal conditions, the yield of GIase_Tfus reached 124.1 U/mL, which is the highest expression level of GIase by recombinant E. coli reported to date. Additionally, the obtained GIase_Tfus was performed to produce high fructose corn syrup (HFCS) with conversion approacing 55 % from glucose (45 %, w/v) to fructose. According to the molecular dynamic simulation, a number of hydrogen bonds existed in the enzyme-substrate complex could stablilize the transient states, and a appreciate reaction distance of M1 catalytic site and oxygen atom of glucose make the reaction proceed easily, thus resulting in the efficient biosynthesis of HFCS. The function of GIase_Tfus renders it a valuable catalyst for HFCS-55 (containing 55 % d-fructose) manufacturing, the most favorable industrial product of HFCS. The efficient expression of GIase_Tfus and its efficient HFCS production lays the foundation for its proming industrial application.