An auto-inducible expression system based on the RhlI-RhlR quorum-sensing regulon for recombinant protein production in E. coli

Efficient 2,3-Butanediol/Acetoin Production Using Whole-Cell Biocatalyst with a New Nadh/Nad(+) Regeneration System

An auto-inducing expression system was developed that could express target genes in S. marcescens MG1. Using this system, MG1 was constructed as a whole-cell biocatalyst to produce 2,3-butanediol/acetoin. Formate dehydrogenase (FDH) and 2,3-butanediol dehydrogenase were expressed together to build an NADH regeneration system to transform diacetyl to 2,3-butanediol. After fermentation, the extract of recombinant S. marcescens MG1ABC (pETDuet-bdhA-fdh) showed 2,3-BDH activity of 57.8 U/mg and FDH activity of 0.5 U/mg. And 27.95 g/L of 2,3-BD was achieved with a productivity of 4.66 g/Lh using engineered S. marcescens MG1(Pswnb+pETDuet-bdhA-fdh) after 6 h incubation. Next, to produce 2,3-butanediol from acetoin, NADH oxidase and 2,3-butanediol dehydrogenase from Bacillus subtilis were co-expressed to obtain a NAD+ regeneration system. After fermentation, the recombinant strain S. marcescens MG1ABC (pSWNB+pETDuet-bdhA-yodC) showed AR activity of 212.4 U/mg and NOX activity of 150.1 U/mg. We obtained 44.9 g/L of acetoin with a productivity of 3.74 g/Lh using S. marcescens MG1ABC (pSWNB+pETDuet-bdhA-yodC). This work confirmed that S. marcescens could be designed as a whole-cell biocatalyst for 2,3-butanediol and acetoin production.

Development of an Autoinducible Plasmid for Recombinant Protein Production

BACKGROUND

The production of recombinant proteins in E. coli involves such factors as host strains, expression vectors, culture media, and induction methods. The typical procedure to produce heterologous proteins consists of the following: (1) insertion of the target gene into a suitable vector to construct an overexpression plasmid, (2) transformation of a strain specialized for protein production with the constructed plasmid DNA, (3) growth of the host in a suitable medium and induction of the protein production at a right moment, and (4) further growth to get the maximum yield. There are hurdles involved in each of these steps, and researchers have developed many materials or methods, which often require special recipes or procedures.

OBJECTIVE

To eliminate the special requirements for the recombinant protein production by using readily available materials. Also to save time and effort in the routine protein production work.

METHOD

We started with a vector capable of producing a target protein fused to the C-terminus of the maltose binding protein (MBP). The mCherry (red fluorescent protein) gene was fused to MBP. It acted as a reporter in the initial screening procedure. The original lethal gene (barnase) was replaced with sacB. We chose 3 stationary phase promoters, and made hybrids of them by mixing halves from each one. The T5 promoter was replaced with these stationary phase promoters or their hybrids. The best plasmid was selected by the color intensity of the cell pellet. MBP and GST genes were inserted in place of sacB, and their production yields were compared with the original plasmid in the conventional way of expression.

RESULTS

We constructed an expression plasmid with an autoinducible promoter working in a host that was not specially designed for protein production and in a TB medium which did not contain any secret ingredient, nor was difficult to prepare unlike Studier's defined medium. This plasmid also contains a color indicator which turns red when protein production is successful. We tested our system with the maltose binding protein (MBP) and the glutathione S-transferase (GST), and showed that both proteins were produced to a level comparable to what the commercial medium and/or the specialized strain yielded.

CONCLUSION

We developed a plasmid equipped with an autoinducible promoter, a hybrid of the two promoters which were activated at the stationary phase. This plasmid does not need a special E. coli strain nor a sophisticated nor an expensive medium. It produces an intense red (or pink) color, which can be used as an indicator of a successful production of the target protein and as a predictive measure of the amount of the produced target protein. We speculate that this plasmid will have its greatest advantage when growing cells at low temperatures which would inevitably take a long time.  .

Scalable, two-stage, autoinduction of recombinant protein expression in E. coli utilizing phosphate depletion

We report the scalable production of recombinant proteins in Escherichia coli, reliant on tightly controlled autoinduction, triggered by phosphate depletion in the stationary phase. The method, reliant on engineered strains and plasmids, enables improved protein expression across scales. Expression levels using this approach have reached as high as 55% of the total cellular protein. The initial use of the method in instrumented fed-batch fermentations enables cell densities of ∼30 gCDW/L and protein titers up to 8.1 ± 0.7 g/L (∼270 mg/gCDW). The process has also been adapted to an optimized autoinduction media, enabling routine batch production at culture volumes of 20 μl (384-well plates), 100 μl (96-well plates), 20 ml, and 100 ml. In batch cultures, cell densities routinely reach ∼5-7 gCDW/L, offering protein titers above 2 g/L. The methodology has been validated with a set of diverse heterologous proteins and is of general use for the facile optimization of routine protein expression from high throughput screens to fed-batch fermentation.

Construction and Characterization of a Medium Copy Number Expression Vector Carrying Auto-Inducible dps Promoter to Overproduce a Bacterial Superoxide Dismutase in Escherichia coli

Medium copy number expression vector and auto-inducible promoter could be a solution for producing recombinant therapeutic proteins in industrial scale regarding plasmid stability, cost, and product quality. This work aimed to construct a medium copy number pBR322-based expression vector carrying auto-inducible promoter, determine its ability to express heterologous gene, and study its segregational stability. Three stationary-phase promoters of Escherichia coli genes (gadA, dps and sbmC) were used to produce a superoxide dismutase from Staphylococcus equorum (rMnSODSeq) coding region from pBR322Δtet (pBR322-mini). Four plasmids were constructed with different promoters, i.e., T7 (pBMsod), gadA (pMCDsod), dps (pCADsod), and sbmC (pCDSsod) using pBR322-mini as backbone. Results showed that rMnSODSeq expression from pBMsod was significantly higher than that from pJExpress414sod (high copy number plasmid). Meanwhile, rMnSODSeq from pCADsod (auto-inducible promoter) was as high as from pBMsod (IPTG-inducible T7 promoter). rMnSODSeq expressed from pCADsod when bacterial cells entered stationary phase appeared as an active protein band of 23.5 kDa when analyzed by zymography and SDS-PAGE. pCADsod displayed the highest stability compared with pBMsod and pJEXpress414sod by plasmid retention assay. We demonstrate the use of an auto-inducible dps promoter to express high level of heterologous protein, an SOD of S. equorum, from a stable expression vector with medium copy number.