Development of a high-copy plasmid for enhanced production of recombinant proteins in Leuconostoc citreum

Production of bioactive recombinant monoclonal antibody fragment in periplasm of Escherichia coli expression system

The microbial expression system (Escherichia coli) is the most widely studied host for the production of biotherapeutic products, such as antibody fragments, single chain variable fragments and nanobodies. However, recombinant biotherapeutic proteins are often expressed as insoluble proteins, thereby limiting the utility of E. coli as expression system. To overcome this limitation, various strategies have been developed, such as changes at DNA level (codon optimization), fusion with soluble tags and variations in process parameters (temperature), and inducer concentration. However, there is no "one size fits all" strategy. The most commonly used approach involves induction at low temperature, as reducing the temperature during cultivation has been reported to increase bioactive protein production in E. coli. In this study, we examine the impact of various process parameters, such as temperature and inducer concentration, as well as, high plasmid copy number vector for achieving enhanced soluble expression of TNFα inhibitor Fab. An interaction amongst these parameters has been observed and their optimization has been demonstrated to result in expression of 30 ± 3 mg/L antibody fragment using E. coli. This case study illustrates how process optimization can contribute toward making biotherapeutics affordable.

Engineering of Leuconostoc citreum for Efficient Bioconversion of Soy Isoflavone Glycosides to Their Aglycone Forms

Soy isoflavones are phytochemicals that possess various beneficial physiological properties such as anti-aging, anti-tumor, and antioxidant properties. Since soy isoflavones exist in glycoside forms, their bioavailability requires initial hydrolysis of the sugar moieties bound to them to be efficiently absorbed through the gut epithelium. Instead of conventional chemical hydrolysis using acids or organic solvents, alternative strategies for enhancing the bioavailability of soy isoflavones using biological methods are gaining attention. Here, we engineered Leuconostoc citreum isolated from Korean kimchi for efficient bioconversion of soy isoflavone glycosides into their aglycone forms to enhance their bioavailability. We first constructed an expression module based on the isoflavone hydrolase (IH)-encoding gene of Bifidobacterium lactis, which mediates conversion of isoflavone glycosides to aglycone forms. Using a high copy number plasmid and bicistronic expression design, the IH was successfully synthesized in L. citreum. Additionally, we determined enzymatic activity of the IH using an in vivo β-glucosidase assay and confirmed its highly efficient bioconversion efficiency for various types of isoflavone glycosides. Finally, we successfully demonstrated that the engineered L. citreum could convert isoflavone glycosides present in fermented soymilk into aglycones.

A brief overview on the application and sources of α-amylase and expression hosts properties in order to production of recombinant α-amylase

By reducing the activation energy, enzymes accelerate the chemical reaction; therefore, they are good alternative for industrial catalysts. Amylase is a suitable enzyme as a catalyst for the chemical decomposition of starch. This enzyme is of great importance, and its production is highly profitable. α-Amylase is among the most important amylases produced naturally by animals, plants, and microorganisms. Still, the α-amylases produced by bacteria have a special place in industry and commerce. Moreover, a large volume of this enzyme can be produced by selecting an appropriate and optimized host to clone and express the α-amylase gene. The present study briefly reviews the structure, application, sources, and hosts used to produce recombinant α-amylase.

Optimized expression of Hfq protein increases Escherichia coli growth

Escherichia coli is a widely used platform for metabolic engineering due to its fast growth and well-established engineering techniques. However, there has been a demand for faster-growing E. coli for higher production of desired substances. Here, to increase the growth of E. coli cells, we optimized the expression level of Hfq protein, which plays an essential role in stress responses. Six variants of the hfq gene with a different ribosome binding site sequence and thereby a different expression level were constructed. When the Hfq expression level was optimized in DH5α, its growth rate was increased by 12.1% and its cell density was also increased by 4.5%. RNA-seq and network analyses revealed the upregulation of stress response genes and metabolic genes, which increases the tolerance against pH changes. When the same strategy was applied to five other E. coli strains (BL21 (DE3), JM109, TOP10, W3110, and MG1655), all their growth rates were increased by 18-94% but not all their densities were increased (- 12 - + 32%). In conclusion, the Hfq expression optimization can increase cell growth rate and probably their cell densities as well. Since the hfq gene is highly conserved across bacterial species, the same strategy could be applied to other bacterial species to construct faster-growing strains.

Biosynthesis and industrial applications of α-amylase: a review

Amylase is amongst the most indispensable enzymes that have a large number of applications in laboratories and industries. Mostly, α-amylase is synthesized from microbes such as bacteria, fungi and yeast. Due to the high demand for α-amylase, its synthesis can be enhanced using recombinant DNA technology, different fermentation methods, less expensive and good carbon and nitrogen sources, and optimizing the various parameters during fermentation, e.g., temperature, pH and fermentation duration. Various methods are used to measure the production and activity of synthesized α-amylase like iodine, DNS, NS and dextrinizing methods. The activity of crude α-amylase can be elevated to the maximum level by optimizing the temperature and pH. Some metals also interact with α-amylase and increase its activity like K⁺, Na⁺, Mg²⁺ and Ca²⁺. Some industries such as starch conversion, food, detergent, paper, textile industries and fuel alcohol production extensively utilize α-amylase for their various purposes.

Development of CRISPR Interference (CRISPRi) Platform for Metabolic Engineering of Leuconostoc citreum and Its Application for Engineering Riboflavin Biosynthesis

Leuconostoc citreum, a hetero-fermentative type of lactic acid bacteria, is a crucial probiotic candidate because of its ability to promote human health. However, inefficient gene manipulation tools limit its utilization in bioindustries. We report, for the first time, the development of a CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) interference (CRISPRi) system for engineering L. citreum. For reliable expression, the expression system of synthetic single guide RNA (sgRNA) and the deactivated Cas9 of Streptococcus pyogenes (SpdCas9) were constructed in a bicistronic design (BCD) platform using a high-copy-number plasmid. The expression of SpdCas9 and sgRNA was optimized by examining the combination of two synthetic promoters and Shine-Dalgarno sequences; the strong expression of sgRNA and the weak expression of SpdCas9 exhibited the most significant downregulation (20-fold decrease) of the target gene (sfGFP), without cell growth retardation caused by SpdCas9 overexpression. The feasibility of the optimized CRISPRi system was demonstrated by modulating the biosynthesis of riboflavin. Using the CRISPRi system, the expression of ribF and folE genes was downregulated (3.3-fold and 5.6-fold decreases, respectively), thereby improving riboflavin production. In addition, the co-expression of the rib operon was introduced and the production of riboflavin was further increased up to 1.7 mg/L, which was 1.53 times higher than that of the wild-type strain.

Fungal β-1,3-1,4-glucanases: production, proprieties and biotechnological applications

β-1,3-1,4-glucanases (or lichenases; EC 3.2.1.73) comprise one of the main enzymes used in industry during recent decades. These enzymes hydrolyze β-glucans containing β-1,3 and β-1,4 linkages, such as cereal β-glucans and lichenan. The β-1,3-1,4-glucanases are produced by a variety of bacteria, fungi, plants and animals. A large number of microbial β-1,3-1,4-glucanases have potential application in industrial processes, such as feed, food and detergent industries. The present review summarizes the available studies with respect to β-1,3-1,4-glucanases production conditions, enzyme biochemical properties and potential industrial application. © 2018 Society of Chemical Industry.

Development of bicistronic expression system for the enhanced and reliable production of recombinant proteins in Leuconostoc citreum

The lactic acid bacteria (LAB) Leuconostoc citreum are non-sporulating hetero-fermentative bacteria that play an important role in the fermented food industry. In this study, for the enhanced and reliable production of recombinant proteins in L. citreum, we developed a bicistronic design (BCD) expression system which includes a short leader peptide (1^st cistron) followed by target genes (2^nd cistron) under the control of a single promoter. Using superfolder green fluorescent protein (sfGFP) as a reporter, the functionality of BCD in L. citreum was verified. Further, to improve the expression in BCD, we tried to engineer a Shine-Dalgarno sequence (SD2) for the 2^nd cistron and a promoter by FACS screening of random libraries, and both strong SD2 (eSD2) and promoter (P_710V4) were successfully isolated. The usefulness of the engineered BCD with P_710V4 and eSD2 was further validated using three model proteins—glutathione-s-transferase, human growth hormone, and α-amylase. All examined proteins were successfully produced with levels highly increased compared with those in the original BCD as well as the monocistronic design (MCD) expression system.

Re-engineering of an Escherichia coli K-12 strain for the efficient production of recombinant human Interferon Gamma

The Escherichia coli phosphoglucose isomerase (pgi) mutant strain GALG20 was developed previously from wild-type K12 strain MG1655 for increased plasmid yield. To investigate the potential effects of the pgi deletion/higher plasmid levels on recombinant human Interferon Gamma (IFN-γ) production, a detailed network of the central metabolic pathway (100 metabolites, 114 reactions) of GALG20 and MG1655 was constructed. Elementary mode analysis (EMA) was then performed to compare the phenotypic spaces of both the strains and to check the effect of the pgi deletion on flux efficiency of each metabolic reaction. The results suggested that pgi deletion increases amino acid biosynthesis and flux efficiency towards IFN-γ synthesis by 11%. To further confirm the qualitative prediction that the pgi mutation favours recombinant human IFN-γ expression, GALG20 and MG1655 were lysogenised, transformed with a plasmid coding for IFN-γ and tested alongside with BL21(DE3) for their expression capabilities in shake flask experiments using complex media. IFN-γ gene expression was analysed by quantifying plasmid and mRNA copy number per cell and IFN-γ protein production level. Specific IFN-γ yields confirmed the in silico metabolic network predictions, with GALG20(DE3) producing 3.0-fold and 1.5-fold more IFN-γ as compared to MG1655(DE3) and BL21(DE3), respectively. Most of the total IFN-γ was expressed as inclusion bodies across the three strains: 95% in GALG20(DE3), 97% in BL21(DE3) and 72% in MG1655(DE3). The copy number of mRNA coding for IFN-γ was found to be higher in GALG20(DE3) as compared to the other two strains. Overall, these findings show that GALG20(DE3) has the potential to become an excellent protein expression strain.

Biotechnological Processes in Microbial Amylase Production

Amylase is an important and indispensable enzyme that plays a pivotal role in the field of biotechnology. It is produced mainly from microbial sources and is used in many industries. Industrial sectors with top-down and bottom-up approaches are currently focusing on improving microbial amylase production levels by implementing bioengineering technologies. The further support of energy consumption studies, such as those on thermodynamics, pinch technology, and environment-friendly technologies, has hastened the large-scale production of the enzyme. Herein, the importance of microbial (bacteria and fungi) amylase is discussed along with its production methods from the laboratory to industrial scales.