Improving the cost effectiveness of enhanced green fluorescent protein production using recombinant Escherichia coli BL21 (DE3): Decreasing the expression inducer concentration.

Green fluorescent protein (GFP) is a globular protein used as biosensor and biomarker in medical and industrial fields. However, due to the expensive production costs of expressing proteins using high-cost inducers like isopropyl-ß-d-1-thiogalactopyranoside (IPTG), the number of GFP applications are still scarce. This work studied the production of enhanced GFP (EGFP) using Escherichia coli BL21 (DE3) [pLysS; pET28(a)], aiming to increase its yield and reduce costs. First, the influence of agitation rate, induction time, and concentration of IPTG in the production of EGFP was evaluated, but only the first two parameters were significant. Subsequently, aiming to reduce costs related to the use of inducer, the IPTG concentration (0.005, 0.010, and 0.025 mM) was decreased and, interestingly, the production levels were maintained or increased. These results show that a proper choice of production conditions, particularly through the decrease of inducer concentration, is effective to reduce the upstream production costs and guarantee high EGFP expression.

Random knock-in expression system for high yield production of heterologous protein in Bacillus subtilis.

Chromosome-integrated recombinant protein expression in bacteria has advantages for the stable maintenance of genes without any use of antibiotics during large-scale fermentation. Even though different levels of gene expression were reported, depending upon their chromosomal position in bacterial species, only a limited number of integration sites have been used in B. subtilis. In this study, we randomly integrated the GFP and AprE expression cassettes into the B. subtilis genome to determine integration sites that can produce a high yield of heterologous protein expression. Our mariner transposon-based expression cassette integration system was able to find integration sites, which can produce up to 2.9-fold and 1.5-fold increased expression of intracellular GFP and extracellular AprE, respectively, compared to the common integration site amyE. By analyzing the location of integration sites, we observed an adjacent promoter effect, gene dosage effect, and gene knock-out effect all complexly contributing to the increased level of integrated gene expression. Besides obtaining a high yield of heterologous protein expression, our system can also provide a wide-range of expression to expand the systematic application for steady-state metabolic protein production.

Mild and cost-effective green fluorescent protein purification employing small synthetic ligands.

The green fluorescent protein (GFP) is a useful indicator in a broad range of applications including cell biology, gene expression and biosensing. However, its full potential is hampered by the lack of a selective, mild and low-cost purification scheme. In order to address this demand, a novel adsorbent was developed as a generic platform for the purification of GFP or GFP fusion proteins, giving GFP a dual function as reporter and purification tag. After screening a solid-phase combinatorial library of small synthetic ligands based on the Ugi-reaction, the lead ligand (A4C7) selectively recovered GFP with 94% yield and 94% purity under mild conditions and directly from Escherichia coli extracts. Adsorbents containing the ligand A4C7 maintained the selectivity to recover other proteins fused to GFP. The performance of A4C7 adsorbents was compared with two commercially available methods (immunoprecipitation and hydrophobic interaction chromatography), confirming the new adsorbent as a low-cost viable alternative for GFP purification.