A Novel Sequence Element Derived from Bacteriophage T7 mRNA Acts as an Enhancer of Translation of the lacZ Gene in Escherichia coli

Efficient heterologous expression of cellobiose 2-epimerase gene in Escherichia coli under the control of T7 lac promoter without addition of IPTG and lactose

In this study, the cellobiose 2-epimerase gene csce from Caldicellulosiruptor saccharolyticus was expressed in Escherichia coli using TB medium containing yeast extract Oxoid and tryptone Oxoid. Interesting, it was found that when the concentration of isopropyl-beta-d-thiogalactopyranoside (IPTG) and lactose was 0 (no addition), the activity of cellobiose 2-epimerase reached 5.88 U/mL. It was 3.70-fold higher than the activity observed when 1.0 mM IPTG was added. When using M9 medium without yeast extract Oxoid and tryptone Oxoid, cellobiose 2-epimerase gene could not be expressed without IPTG and lactose. However, cellobiose 2-epimerase gene could be expressed when yeast extract Oxoid or tryptone Oxoid was added, indicating that these supplements contained inducers for gene expression. In the absence of IPTG and lactose, the addition of soy peptone Angel-1 or yeast extract Angel-1 to M9 medium significantly upregulated the expression of cellobiose 2-epimerase gene in E. coli BL21 pET28a-csce, and these inductions led to higher expression levels compared to tryptone Oxoid or yeast extract Oxoid. The relative transcription level of csce was consistent with its expression level in E. coli BL21 pET28a-csce. In the medium TB without IPTG and lactose and containing yeast extract Angel-1 and soy peptone Angel-1, the activity of cellobiose 2-epimerase reached 6.88 U/mL, representing a 2.2-fold increase compared to previously reported maximum activity in E. coli. The significance of this study lies in its implications for efficient heterologous expression of recombinant enzyme proteins in E. coli without the need for IPTG and lactose addition.

Recombinant expression and purification of phenylalanyl-tRNA synthetase from wheat: a long-lasting poly(U)-dependent poly(Phe) synthesis system

Synthetic genes for the two subunits of phenylalanyl-tRNA synthetase (PheRS) from wheat were expressed in Escherichia coli. When each gene was induced individually, the α subunit with a cleavable 6 × His tag at the amino terminus was largely soluble, while the β subunit was almost completely insoluble. When the two subunits were co-expressed, a soluble fraction containing the two subunits were obtained. This was purified by a standard method in which the tag was cleaved off with a specific protease after affinity purification. As the sample contained slightly more PheRSα than PheRSβ, we further resolved the sample by gel filtration to obtain the fraction that showed the size of the conventional α2β2 tetrameric complex and contains an almost equal amount of the two subunits. The final yield was 0.6 mg per 1 liter of the culture medium, and the specific activity was 28 nmol min-1 mg-1, which was higher than that of a fraction purified from wheat germ. This recombinant PheRS was used, along with purified samples of the elongation factors and the ribosomes from wheat germ, for a poly(U)-dependent poly(Phe) synthesis reaction. The reaction was dependent on the added components and lasted for more than several hours.

Borrelia burgdorferi BB0346 is an Essential, Structurally Variant LolA Homolog that is Primarily Required for Homeostatic Localization of Periplasmic Lipoproteins

In diderm bacteria, the Lol pathway canonically mediates the periplasmic transport of lipoproteins from the inner membrane (IM) to the outer membrane (OM) and therefore plays an essential role in bacterial envelope homeostasis. After extrusion of modified lipoproteins from the IM via the LolCDE complex, the periplasmic chaperone LolA carries lipoproteins through the periplasm and transfers them to the OM lipoprotein insertase LolB, itself a lipoprotein with a LolA-like fold. Yet, LolB homologs appear restricted to γ-proteobacteria and are missing from spirochetes like the tick-borne Lyme disease pathogen Borrelia burgdorferi, suggesting a different hand-off mechanism at the OM. Here, we solved the crystal structure of the B. burgdorferi LolA homolog BB0346 (LolABb) at 1.9 Å resolution. We identified multiple structural deviations in comparative analyses to other solved LolA structures, particularly a unique LolB-like protruding loop domain. LolABb failed to complement an Escherichia coli lolA knockout, even after codon optimization, signal I peptide adaptation, and a C-terminal chimerization which had allowed for complementation with an α-proteobacterial LolA. Analysis of a conditional B. burgdorferi lolA knockout strain indicated that LolABb was essential for growth. Intriguingly, protein localization assays indicated that initial depletion of LolABb led to an emerging mislocalization of both IM and periplasmic OM lipoproteins, but not surface lipoproteins. Together, these findings further support the presence of two separate primary secretion pathways for periplasmic and surface OM lipoproteins in B. burgdorferi and suggest that the distinct structural features of LolABb allow it to function in a unique LolB-deficient lipoprotein sorting system.

Modifications of the 5' region of the CASPONTM tag's mRNA further enhance soluble recombinant protein production in Escherichia coli

BACKGROUND

Escherichia coli is one of the most commonly used host organisms for the production of biopharmaceuticals, as it allows for cost-efficient and fast recombinant protein expression. However, challenging proteins are often produced with low titres or as inclusion bodies, and the manufacturing process needs to be developed individually for each protein. Recently, we developed the CASPONTM technology, a generic fusion tag-based platform process for high-titer soluble expression including a standardized downstream processing and highly specific enzymatic cleavage of the fusion tag. To assess potential strategies for further improvement of the N-terminally fused CASPONTM tag, we modified the 5'UTR and 5' region of the tag-coding mRNA to optimize the ribosome-mRNA interactions.

RESULTS

In the present work, we found that by modifying the 5'UTR sequence of a pET30acer plasmid-based system, expression of the fusion protein CASPONTM-tumour necrosis factor α was altered in laboratory-scale carbon-limited fed-batch cultivations, but no significant increase in expression titre was achieved. Translation efficiency was highest for a construct carrying an expression enhancer element and additionally possessing a very favourable interaction energy between ribosome and mRNA (∆Gtotal). However, a construct with comparatively low transcriptional efficiency, which lacked the expression enhancer sequence and carried the most favourable ∆Gtotal tested, led to the highest recombinant protein formation alongside the reference pET30a construct. Furthermore, we found, that by introducing synonymous mutations within the nucleotide sequence of the T7AC element of the CASPONTM tag, utilizing a combination of rare and non-rare codons, the free folding energy of the nucleotides at the 5' end (-4 to + 37) of the transcript encoding the CASPONTM tag increased by 6 kcal/mol. Surprisingly, this new T7ACrare variant led to improved recombinant protein titres by 1.3-fold up to 5.3-fold, shown with three industry-relevant proteins in lab-scale carbon limited fed-batch fermentations under industrially relevant conditions.

CONCLUSIONS

This study reveals some of the complex interdependencies between the ribosome and mRNA that govern recombinant protein expression. By modifying the 5'UTR to obtain an optimized interaction energy between the mRNA and the ribosome (ΔGtotal), transcript levels were changed, highlighting the different translation efficiencies of individual transcripts. It was shown that the highest recombinant titre was not obtained by the construct with the most efficient translation but by a construct with a generally high transcript amount coupled with a favourable ΔGtotal. Furthermore, an unexpectedly high potential to enhance expression by introducing silent mutations including multiple rare codons into the 5'end of the CAPONTM tag's mRNA was identified. Although the titres of the fusion proteins were dramatically increased, no formation of inclusion bodies or negative impact on cell growth was observed. We hypothesize that the drastic increase in titre is most likely caused by better ribosomal binding site accessibility. Our study, which demonstrates the influence of changes in ribosome-mRNA interactions on protein expression under industrially relevant production conditions, opens the door to the applicability of the new T7ACrare tag in biopharmaceutical industry using the CASPONTM platform process.

Engineering cellular communication between light-activated synthetic cells and bacteria

Gene-expressing compartments assembled from simple, modular parts, are a versatile platform for creating minimal synthetic cells with life-like functions. By incorporating gene regulatory motifs into their encapsulated DNA templates, in situ gene expression and, thereby, synthetic cell function can be controlled according to specific stimuli. In this work, cell-free protein synthesis within synthetic cells was controlled using light by encoding genes of interest on light-activated DNA templates. Light-activated DNA contained a photocleavable blockade within the T7 promoter region that tightly repressed transcription until the blocking groups were removed with ultraviolet light. In this way, synthetic cells were activated remotely, in a spatiotemporally controlled manner. By applying this strategy to the expression of an acyl homoserine lactone synthase, BjaI, quorum-sensing-based communication between synthetic cells and bacteria was controlled with light. This work provides a framework for the remote-controlled production and delivery of small molecules from nonliving matter to living matter, with applications in biology and medicine.

The production of the first functional antibody mimetic in higher plants: the chloroplast makes the DARPin G3 for HER2 imaging in oncology

Background

Designed mimetic molecules are attractive tools in biopharmaceuticals and synthetic biology. They require mass and functional production for the assessment of upcoming challenges in the near future. The DARPin family is considered a mimetic pharmaceutical peptide group with high affinity binding to specific targets. DARPin G3 is designed to bind to the HER2 (human epidermal growth factor receptor 2) tyrosine kinase receptor. Overexpression of HER2 is common in some cancers, including breast cancer, and can be used as a prognostic and predictive tool for cancer. The chloroplasts are cost-effective alternatives, equal to, and sometimes better than, bacterial, yeast, or mammalian expression systems. This research examined the possibility of the production of the first antibody mimetic, DARPin G3, in tobacco chloroplasts for HER2 imaging in oncology.

Results

The chloroplast specific DARPin G3 expression cassette was constructed and transformed into N. tabacum chloroplasts. PCR and Southern blot analysis confirmed integration of transgenes as well as chloroplastic and cellular homoplasmy. The Western blot analysis and ELISA confirmed the production of DARPin G3 at the commercial scale and high dose with the rate of 20.2% in leaf TSP and 33.7% in chloroplast TSP. The functional analysis by ELISA confirmed the binding of IMAC purified chloroplast-made DARPin G3 to the extracellular domain of the HER2 receptor with highly effective picomolar affinities. The carcinoma cellular studies by flow cytometry and immunofluorescence microscopy confirmed the correct functioning by the specific binding of the chloroplast-made DARPin G3 to the HER2 receptor on the surface of HER2-positive cancer cell lines.

Conclusion

The efficient functional bioactive production of DARPin G3 in chloroplasts led us to introduce plant chloroplasts as the site of efficient production of the first antibody mimetic molecules. This report, as the first case of the cost-effective production of mimetic molecules, enables researchers in pharmaceuticals, synthetic biology, and bio-molecular engineering to develop tool boxes by producing new molecular substitutes for diverse purposes.

Comparative Analysis of Catabolic and Anabolic Dehydroshikimate Dehydratases for 3,4-DHBA Production in Escherichia coli

The production of 3,4-dihydroxybenzoic acid (3,4-DHBA or protocatechuate) is a relevant task owing to 3,4-DHBA’s pharmaceutical properties and its use as a precursor for subsequent synthesis of high value-added chemicals. The microbial production of 3,4-DHBA using dehydroshikimate dehydratase (DSD) (EC: 4.2.1.118) has been demonstrated previously. DSDs from soil-dwelling organisms (where DSD is involved in quinate/shikimate degradation) and from Bacillus spp. (synthesizing the 3,4-DHBA-containing siderophore) were compared in terms of the kinetic properties and their ability to produce 3,4-DHBA. Catabolic DSDs from Corynebacterium glutamicum (QsuB) and Neurospora crassa (Qa-4) had higher K_m (1 and 0.6 mM, respectively) and k_cat (61 and 220 s⁻¹, respectively) than biosynthetic AsbF from Bacillus thuringiensis (K_m~0.04 mM, k_cat~1 s⁻¹). Product inhibition was found to be a crucial factor when choosing DSD for strain development. AsbF was more inhibited by 3,4-DHBA (IC₅₀~0.08 mM), and Escherichia coli MG1655 ΔaroE P_lacUV5-asbF_attφ80 strain provided only 0.2 g/L 3,4-DHBA in test-tube fermentation. Isogenic strains MG1655 ΔaroE P_lacUV5-qsuB_attφ80 and MG1655 ΔaroE P_lacUV5-qa-4_attφ80 expressing QsuB and Qa-4 with IC₅₀ ~0.35 mM and ~0.64 mM, respectively, accumulated 2.7 g/L 3,4-DHBA under the same conditions.

Construction of Recombinant Lactococcus lactis Strain Expressing VP1 Fusion Protein of Duck Hepatitis A Virus Type 1 and Evaluation of Its Immune Effect

With the continuous development of duck farming and the increasing breeding density, the incidence of duck hepatitis A virus type 1 (DHAV-1) has been on the rise, seriously endangering the development of duck farming. To reduce the use of antibiotics in duck breeding, susceptibility risks and mortality, and avoid virulence recovery and immune failure risk, this study aims to develop a new type of mucosal immune probiotics and make full use of molecular biology techniques, on the level of genetic engineering, to modify Lactococcus lactis (L. lactis). In this study, a secretory recombinant L. lactis named MG1363-VP1 with an enhanced Green Fluorescent Protein (eGFP) and translation enhancer T7g10L was constructed, which could express the VP1-eGFP fusion protein of DHAV-1. The animal experiment in ducklings was performed to detect the immune response and protection effect of oral microecologics by recombinant L. lactis. The results showed that oral L. lactis MG1363-VP1 significantly induced the body’s humoral immune system and mucosal immune system to produce specific anti-VP1 IgG antibodies and mucosal secretory immunoglobulin A (sIgA) for DHAV-1 in ducklings, and cytokines including interleukin-2 (IL-2), interleukin-4 (IL-4), interleukin-10 (IL-10), and interferon gamma (IFN-γ). The mortality rate was monitored simultaneously by the natural infestation in the process of production and breeding; notably, the ducklings vaccinated with L. lactis MG1363-VP1 were effectively protected against the nature infection of DHAV-1. The recombinant L. lactis MG1363-VP1 constructed in this study provides a new means of preventing and controlling DHAV-1 infection in the future.

Translation initiation from sequence variants of the bacteriophage T7 g10RBS in Escherichia coli and Agrobacterium fabrum

BACKGROUND

The bacteriophage T7 gene 10 ribosome binding site (g10RBS) has long been used for robust expression of recombinant proteins in Escherichia coli. This RBS consists of a Shine-Dalgarno (SD) sequence augmented by an upstream translational "enhancer" (Enh) element, supporting protein production at many times the level seen with simple synthetic SD-containing sequences. The objective of this study was to dissect the g10RBS to identify simpler derivatives that exhibit much of the original translation efficiency.

METHODS AND RESULTS

Twenty derivatives of g10RBS were tested using multiple promoter/reporter gene contexts. We have identified one derivative (which we call "CON_G") that maintains 100% activity in E. coli and is 33% shorter. Further minimization of CON_G results in variants that lose only modest amounts of activity. Certain nucleotide substitutions in the spacer region between the SD sequence and initiation codon show strong decreases in translation. When testing these 20 derivatives in the alphaproteobacterium Agrobacterium fabrum, most supported strong reporter protein expression that was not dependent on the Enh.

CONCLUSIONS

The g10RBS derivatives tested in this study display a range of observed activity, including a minimized version (CON_G) that retains 100% activity in E. coli while being 33% shorter. This high activity is evident in two different promoter/reporter sequence contexts. The array of RBS sequences presented here may be useful to researchers in need of fine-tuned expression of recombinant proteins of interest.

Influence of the expression vector and its elements on recombinant human prolactin synthesis in Escherichia coli; co-directional orientation of replication and transcription is highly critical

The aim of the present work was to define a bacterial expression system that is particularly efficient for the synthesis of recombinant human prolactin (hPRL). In previous work, based on experiments that were basically carried out in parallel with the present ones, the synthesis of rec-hPRL by the p1813-hPRL vector in E. coli HB2151 was >500 mg/L, while it was much lower here (2.5-4-fold), in the RB791 and RRI strains. The highest positive influence on rec-hPRL synthesis was due to the transcription-replication co-orientation of hPRL cDNA and the ori/antibiotic resistance gene, responsible for up to a ~ 5-6-fold higher expression yield. In conclusion, this work confirmed that each bacterial strain of E. coli has a genetic background that can allow a different level of heterologous protein synthesis. The individual study of each element indicated that its action critically depends on the reading orientation in which it is located inside the vector: co-directional orientation of replication and transcription, in fact, greatly increased the level of rec-hPRL expression.

Guidelines for nucleic acid template design for optimal cell-free protein synthesis using an Escherichia coli reconstituted system or a lysate-based system

Cell-free protein synthesis is an attractive method for generating enzyme/protein variants for simplified functional analysis as both in vitro protein expression and analysis may often be performed in a single vial or well. Today, researchers may choose from multiple commercial cell lysate products or reconstituted systems which are compatible with either mRNA, linear DNA or plasmid DNA templates. Here we provide guidance for optimal design of the genetic elements within linear and plasmid DNA templates which are required to reliably practice cell-free protein synthesis. Protocols are presented for generating linear DNA templates, and data are presented to show that linear DNA templates may in many cases provide robust protein yields even when employing an Escherichia coli lysate for protein synthesis. Finally, the use of linear DNA templates makes it possible to bypass all cell cultivation steps and proceed from PCR amplification of synthetic DNA to generation of target protein in a matter of hours.

Improved Dynamic Range of a Rhamnose-Inducible Promoter for Gene Expression in Burkholderia spp

A diverse genetic toolkit is critical for understanding bacterial physiology and genotype-phenotype relationships. Inducible promoter systems are an integral part of this toolkit. In Burkholderia and related species, the l-rhamnose-inducible promoter is among the first choices due to its tight control and the lack of viable alternatives. To improve upon its maximum activity and dynamic range, we explored the effect of promoter system modifications in Burkholderia cenocepacia with a LacZ-based reporter. By combining the bacteriophage T7 gene 10 stem-loop and engineered rhaI transcription factor-binding sites, we obtained a rhamnose-inducible system with a 6.5-fold and 3.0-fold increases in maximum activity and dynamic range, respectively, compared to the native promoter. We then added the modified promoter system to pSCrhaB2 and pSC201, common genetic tools used for plasmid-based and chromosome-based gene expression, respectively, in Burkholderia, creating pSCrhaB2plus and pSC201plus. We demonstrated the utility of pSCrhaB2plus for gene expression in B. thailandensis, B. multivorans, and B. vietnamiensis and used pSC201plus to control highly expressed essential genes from the chromosome of B. cenocepacia. The utility of the modified system was demonstrated as we recovered viable mutants to control ftsZ, rpoBC, and rpsF, whereas the unmodified promoter was unable to control rpsF. The modified expression system allowed control of an essential gene depletion phenotype at lower levels of l-rhamnose, the inducer. pSCRhaB2plus and pSC201plus are expected to be valuable additions to the genetic toolkit for Burkholderia and related species. IMPORTANCE Species of Burkholderia are dually recognized as being of attractive biotechnological potential but also opportunistic pathogens for immunocompromised individuals. Understanding the genotype-phenotype relationship is critical for synthetic biology approaches in Burkholderia to disentangle pathogenic from beneficial traits. A diverse genetic toolkit, including inducible promoters, is the foundation for these investigations. Thus, we sought to improve on the commonly used rhamnose-inducible promoter system. Our modifications resulted in both higher levels of heterologous protein expression and broader control over highly expressed essential genes in B. cenocepacia. The significance of our work is in expanding the genetic toolkit to enable more comprehensive studies into Burkholderia and related bacteria.

Folding of Circularly Permuted and Split Outer Membrane Protein F via Electrostatic Interactions with Terminal Residues

Membrane proteins are essential targets in drug design, biosensing, and catalysis. In this study, we explored the folding of engineered outer membrane protein F (OmpF), an abundant and functional β-barrel protein expressed in Gram-negative bacteria. We carried out circular permutation, splitting and self-complementation, and point mutation. The folding efficiency and kinetic analyses demonstrated that the N- and C-terminal residues of OmpF played critical roles in folding via electrostatic interactions with lipid headgroups. Our results indicate that native porins without charged terminal residues may be tightly downregulated to retain the integrity of the outer membrane, and this modification may facilitate the insertion and folding of modified membrane proteins under in vitro and in vivo conditions for various applications.

Plasmid Design for Tunable Two-Enzyme Co-Expression Promotes Whole-Cell Production of Cellobiose

Catalyst development for biochemical cascade reactions often follows a "whole-cell-approach" in which a single microbial cell is made to express all required enzyme activities. Although attractive in principle, the approach can encounter limitations when efficient overall flux necessitates precise balancing between activities. This study shows an effective integration of major design strategies from synthetic biology to a coherent development of plasmid vectors, enabling tunable two-enzyme co-expression in E. coli, for whole-cell-production of cellobiose. An efficient transformation of sucrose and glucose into cellobiose by a parallel (countercurrent) cascade of disaccharide phosphorylases requires the enzyme co-expression to cope with large differences in specific activity of cellobiose phosphorylase (14 U mg^-1 ) and sucrose phosphorylase (122 U mg^-1 ). Mono- and bicistronic co-expression strategies controlling transcription, transcription-translation coupling or plasmid replication are analyzed for effect on activity and stable producibility of the whole-cell-catalyst. A key role of bom (basis of mobility) for plasmid stability dependent on the ori is reported and the importance of RBS (ribosome binding site) strength is demonstrated. Whole cell catalysts show high specific rates (460 µmol cellobiose min^-1  g^-1 dry cells) and performance metrics (30 g L^-1 ; ∼82% yield; 3.8 g L^-1 h^-1 overall productivity) promising for cellobiose production.

Metagenomics-Guided Discovery of Potential Bacterial Metallothionein Genes from the Soil Microbiome That Confer Cu and/or Cd Resistance

Metallothionein (MT) genes are valuable genetic materials for developing metal bioremediation tools. Currently, a limited number of prokaryotic MTs have been experimentally identified, which necessitates the expansion of bacterial MT diversity. In this study, we conducted a metagenomics-guided analysis for the discovery of potential bacterial MT genes from the soil microbiome. More specifically, we combined resistance gene enrichment through diversity loss, metagenomic mining with a dedicated MT database, evolutionary trace analysis, DNA chemical synthesis, and functional genomic validation to identify novel MTs. Results showed that Cu stress induced a compositional change in the soil microbiome, with an enrichment of metal-resistant bacteria in soils with higher Cu concentrations. Shotgun metagenomic sequencing was performed to obtain the gene pool of environmental DNA (eDNA), which was subjected to a local BLAST search against an MT database for detecting putative MT genes. Evolutional trace analysis led to the identification of 27 potential MTs with conserved cysteine/histidine motifs different from those of known prokaryotic MTs. Following chemical synthesis of these 27 potential MT genes and heterologous expression in Escherichia coli, six of them were found to improve the hosts' growth substantially and enhanced the hosts' sorption of Cu, Cd, and Zn, among which MT5 led to a 13.7-fold increase in Cd accumulation. Furthermore, four of them restored Cu and/or Cd resistance in two metal-sensitive E. coli strains.IMPORTANCE The metagenomics-guided procedure developed here bypasses the difficulties encountered in classic PCR-based approaches and led to the discovery of novel MT genes, which may be useful in developing bioremediation tools. The procedure used here expands our knowledge on the diversity of bacterial MTs in the environment and may also be applicable to identify other functional genes from eDNA.

In vitro self-replication and multicistronic expression of large synthetic genomes

The generation of a chemical system capable of replication and evolution is a key objective of synthetic biology. This could be achieved by in vitro reconstitution of a minimal self-sustaining central dogma consisting of DNA replication, transcription and translation. Here, we present an in vitro translation system, which enables self-encoded replication and expression of large DNA genomes under well-defined, cell-free conditions. In particular, we demonstrate self-replication of a multipartite genome of more than 116 kb encompassing the full set of Escherichia coli translation factors, all three ribosomal RNAs, an energy regeneration system, as well as RNA and DNA polymerases. Parallel to DNA replication, our system enables synthesis of at least 30 encoded translation factors, half of which are expressed in amounts equal to or greater than their respective input levels. Our optimized cell-free expression platform could provide a chassis for the generation of a partially self-replicating in vitro translation system.

Compensating for over-production inhibition of the Hsmar1 transposon in Escherichia coli using a series of constitutive promoters

Background

Transposable elements (TEs) are a diverse group of self-mobilizing DNA elements. Transposition has been exploited as a powerful tool for molecular biology and genomics. However, transposition is sometimes limited because of auto-regulatory mechanisms that presumably allow them to cohabit within their hosts without causing excessive genomic damage. The papillation assay provides a powerful visual screen for hyperactive transposases. Transposition is revealed by the activation of a promoter-less lacZ gene when the transposon integrates into a non-essential gene on the host chromosome. Transposition events are detected as small blue speckles, or papillae, on the white background of the main Escherichia coli colony.

Results

We analysed the parameters of the papillation assay including the strength of the transposase transcriptional and translational signals. To overcome certain limitations of inducible promoters, we constructed a set of vectors based on constitutive promoters of different strengths to widen the range of transposase expression. We characterized and validated our expression vectors with Hsmar1, a member of the mariner transposon family. The highest rate of transposition was observed with the weakest promoters. We then took advantage of our approach to investigate how the level of transposition responds to selected point mutations and the effect of joining the transposase monomers into a single-chain dimer.

Conclusions

We generated a set of vectors to provide a wide range of transposase expression which will be useful for screening libraries of transposase mutants. The use of weak promoters should allow screening for truly hyperactive transposases rather than those that are simply resistant to auto-regulatory mechanisms, such as overproduction inhibition (OPI). We also found that mutations in the Hsmar1 dimer interface provide resistance to OPI in bacteria, which could be valuable for improving bacterial transposon mutagenesis techniques.

Protective Immunity against Canine Distemper Virus in Dogs Induced by Intranasal Immunization with a Recombinant Probiotic Expressing the Viral H Protein

Canine distemper virus (CDV) elicits a severe contagious disease in a broad range of hosts. CDV mortality rates are 50% in domestic dogs and 100% in ferrets. Its primary infection sites are respiratory and intestinal mucosa. This study aimed to develop an effective mucosal CDV vaccine using a non-antibiotic marked probiotic pPG^ΔCm-T7g10-EGFP-H/L. casei 393 strain expressing the CDV H protein. Its immunogenicity in BALB/c mice was evaluated using intranasal and oral vaccinations, whereas in dogs the intranasal route was used for vaccination. Our results indicate that this probiotic vaccine can stimulate a high level of secretory immunoglobulin A (sIgA)-based mucosal and IgG-based humoral immune responses in mice. SIgA levels in the nasal lavage and lungs were significantly higher in intranasally vaccinated mice than those in orally vaccinated mice. Both antigen-specific IgG and sIgA antibodies were effectively elicited in dogs through the intranasal route and demonstrated superior immunogenicity. The immune protection efficacy of the probiotic vaccine was evaluated by challenging the immunized dogs with virulent CDV 42 days after primary immunization. Dogs of the pPG^ΔCm-T7g10-EGFP-H/L. casei 393 group were completely protected against CDV. The proposed probiotic vaccine could be promising for protection against CDV infection in dogs.

Recombinant Lactobacillus casei Expressing Capsid Protein VP60 can Serve as Vaccine Against Rabbit Hemorrhagic Disease Virus in Rabbits

Rabbit hemorrhagic disease virus (RHDV) is the causative agent of rabbit hemorrhagic disease (RHD). RHD, characterized by hemorrhaging, liver necrosis, and high morbidity and mortality in rabbits and hares, causes severe economic losses in the rabbit industry worldwide. Due to the lack of an efficient in-vitro propagation system for RHDV, the current vaccine is produced via chemical inactivation of crude RHDV preparation derived from the livers of infected rabbits. Inactivated vaccines are effective for controlling RHD, but the potential problems of biosafety and animal welfare have negative effects on the application of inactivated vaccines. In this study, an oral Lactobacillus casei (L. casei) vaccine was used as an antigen delivery system to express RHDV capsid protein VP60(VP1)-eGFP fusion protein. The expression of the recombinant protein was confirmed via western blotting and immunofluorescence (IFA). Our results indicate that oral administration of this probiotic vaccine can stimulate secretory immunoglobulin A (SIgA)-based mucosal and IgG-based humoral immune responses in rabbits. The immunized rabbits were completely protected against challenge with RHDV. Our findings indicate that the L. casei expression system is a new strategy for the development of a safe and efficient vaccine against RHDV.

The biosynthetic origin of psychoactive kavalactones in kava

Kava (Piper methysticum) is an ethnomedicinal shrub native to the Polynesian islands with well-established anxiolytic and analgesic properties. Its main psychoactive principles, kavalactones, form a unique class of polyketides that interact with the human central nervous system through mechanisms distinct from those of conventional psychiatric drugs. However, an unknown biosynthetic machinery and difficulty in chemical synthesis hinder the therapeutic use of kavalactones. In addition, kava also produces flavokavains, which are chalconoids with anticancer properties structurally related to kavalactones. Here, we report de novo elucidation of the key enzymes of the kavalactone and flavokavain biosynthetic network. We present the structural basis for the evolutionary development of a pair of paralogous styrylpyrone synthases that establish the kavalactone scaffold and the catalytic mechanism of a regio- and stereo-specific kavalactone reductase that produces a subset of chiral kavalactones. We further demonstrate the feasibility of engineering styrylpyrone production in heterologous hosts, thus opening a way to develop kavalactone-based non-addictive psychiatric therapeutics through synthetic biology.

Oral immunization of mice with a probiotic Lactobacillus casei constitutively expressing the α-toxoid induces protective immunity against Clostridium perfringens α-toxin

Clostridium perfringens α-toxin is one of the major virulence factors during C. perfringens infection, causing hemolysis of erythrocytes in various species. Here, genetically engineered Lactobacillus casei (pPG-α/L. casei 393) constitutively expressing the toxoid of C. perfringens α-toxin was generated and its immunogenicity in mice for induction of protective immunity against the α-toxin was evaluated via oral immunization. The α-toxoid was constitutively expressed by pPG-α/L. casei 393 without a specific inducer, as confirmed by western blotting, laser confocal microscopy, and flow cytometry. In an experiment on BALB/c mice to evaluate the oral immunogenicity of pPG-α/L. casei 393, significant levels of a specific secretory IgA (sIgA) antibody in the intestinal mucus and feces and an IgG antibody in the serum of the probiotic vaccine group were detected after booster immunization (p < 0.05) as compared with the pPG/L. casei 393 and PBS control groups. These antibodies effectively neutralized C. perfringens natural α-toxin. Moreover, significantly higher levels of cytokines IL-2, IL-4, IL-10, IL-12, IL-17, and interferon (IFN) γ in the serum and increased proliferation of spleen lymphocytes obtained from mice orally immunized with pPG-α/L. casei 393 were detected. With a commercial C. perfringens type A inactivated vaccine as a control, immune protection provided by the probiotic vaccine against C. perfringens α-toxin was evaluated, and 90% and 80% protection rates were observed, respectively. Therefore, strain pPG-α/L. casei 393 effectively elicited mucosal, humoral, and cellular immunity, suggesting that pPG-α/L. casei 393 is a promising candidate for development of a vaccine against C. perfringens α-toxin.

A Mini-ISY100 Transposon Delivery System Effective in γ Proteobacteria

Transposons are invaluable biological tools for the genetic manipulation of microorganisms. ISY100 from Synechocystis sp. PCC6803 is a member of the Tc1/mariner/IS630 superfamily, and is characterized by high transposition efficiency and a strong preference for TA target sequences. In this paper, we describe the design and application of a mini-ISY100 suicide vector for the in vivo creation of stable random transposon insertion libraries. The system was successfully applied in seven species belonging to four different orders of γ proteobacteria. In all cases, delivery using conjugation consistently showed the highest transposition efficiency compared to chemical transformation or electroporation. We determined the frequency of transposon insertions in all the species and proved the utility of the system by identifying genes involved in colony coloration in Shewanella oneidensis. The ease and the efficiency of the protocol developed here allow the creation of complete knock-out libraries in an extensive range of host microorganisms in less than a week with no requirement for preparatory modification.

Intercistronic expression elements (IEE) from the chloroplast of Chlamydomonas reinhardtii can be used for the expression of foreign genes in synthetic operons

Two intercistronic regions were identified as functional intercistronic expression elements (IEE) for the simultaneous expression of aphA-6 and gfp in a synthetic operon in the chloroplast of C. reinhardtii. Chlamydomonas reinhardtii, a biflagellate photosynthetic microalga, has been widely used in basic and applied science. Already three decades ago, Chlamydomonas had its chloroplast genome transformed and to this day constitutes the only alga routinely used in transplastomic technology. Despite the fact that over a 100 foreign genes have been expressed from the chloroplast genome, little has been done to address the challenge of expressing multiple genes in the form of operons, a development that is needed and crucial to push forward metabolic engineering and synthetic biology in this organism. Here, we studied five intercistronic regions and investigated if they can be used as intercistronic expression elements (IEE) in synthetic operons to drive the expression of foreign genes in the chloroplast of C. reinhardtii. The intercistronic regions were those from the psbB-psbT, psbN-psbH, psaC-petL, petL-trnN and tscA-chlN chloroplast operons, and the foreign genes were the aminoglycoside 3'-phosphotransferase (aphA-6), which confers resistance to kanamycin, and the green fluorescent protein gene (gfp). While all the intercistronic regions yielded lines that were resistant to kanamycin, only two (obtained with intercistronic regions from psbN-psbH and tscA-chlN) were identified as functional IEEs, yielding lines in which the second cistron (gfp) was translated and generated GFP. The IEEs we have identified could be useful for the stacking of genes for metabolic engineering or synthetic biology circuits in the chloroplast of C. reinhardtii.

Modernized Tools for Streamlined Genetic Manipulation and Comparative Study of Wild and Diverse Proteobacterial Lineages

A great challenge in microbiota research is the immense diversity of symbiotic bacteria with the capacity to impact the lives of plants and animals. Moving beyond correlative DNA sequencing-based studies to define the cellular and molecular mechanisms by which symbiotic bacteria influence the biology of their hosts is stalling because genetic manipulation of new and uncharacterized bacterial isolates remains slow and difficult with current genetic tools. Moreover, developing tools de novo is an arduous and time-consuming task and thus represents a significant barrier to progress. To address this problem, we developed a suite of engineering vectors that streamline conventional genetic techniques by improving postconjugation counterselection, modularity, and allelic exchange. Our modernized tools and step-by-step protocols will empower researchers to investigate the inner workings of both established and newly emerging models of bacterial symbiosis.

Correlating the presence of bacteria and the genes they carry with aspects of plant and animal biology is rapidly outpacing the functional characterization of naturally occurring symbioses. A major barrier to mechanistic studies is the lack of tools for the efficient genetic manipulation of wild and diverse bacterial isolates. To address the need for improved molecular tools, we used a collection of proteobacterial isolates native to the zebrafish intestinal microbiota as a testbed to construct a series of modernized vectors that expedite genetic knock-in and knockout procedures across lineages. The innovations that we introduce enhance the flexibility of conventional genetic techniques, making it easier to manipulate many different bacterial isolates with a single set of tools. We developed alternative strategies for domestication-free conjugation, designed plasmids with customizable features, and streamlined allelic exchange using visual markers of homologous recombination. We demonstrate the potential of these tools through a comparative study of bacterial behavior within the zebrafish intestine. Live imaging of fluorescently tagged isolates revealed a spectrum of distinct population structures that differ in their biogeography and dominant growth mode (i.e., planktonic versus aggregated). Most striking, we observed divergent genotype-phenotype relationships: several isolates that are predicted by genomic analysis and in vitro assays to be capable of flagellar motility do not display this trait within living hosts. Together, the tools generated in this work provide a new resource for the functional characterization of wild and diverse bacterial lineages that will help speed the research pipeline from sequencing-based correlations to mechanistic underpinnings.

The Construction of an Engineered Bacterial Strain and Its Application in Accumulating Mercury from Wastewater

To remove organic and inorganic mercury from wastewater, an engineered bacterial strain, BL21-7, was constructed that contained the artificial operon P16S-g10-merT-merP-merB1-merB2-ppk-rpsT. For BL21-7, the minimum inhibitory concentrations of mercuric chloride, methylmercury chloride and phenylmercury chloride in Luria-Bertani (LB) medium were 100 µmol/L, 60 µmol/L and 80 µmol/L, respectively. After being cultured in three media (liquid LB containing 80 µmol/L mercuric chloride, 40 µmol/L methylmercury chloride or 60 µmol/L phenylmercury chloride) for 72 h, the engineered bacteria accumulated up to 70.5 ± 1.5 µmol/L, 33.5 ± 3.2 µmol/L and 45.3 ± 3.7 µmol/L of mercury, respectively. In the presence of 10 µmol/L Cd2+, 10 µmol/L Pb2+ or 10 µmol/L Cu2+, the accumulation of mercurial derivatives by BL21-7 was not affected. BL21-7 could accumulate mercury well in media with pH values ranging from 5 to 8 and it could work well at temperatures from 25 °C to 37 °C. After BL21-7 was added to wastewater and cultured for 24 h, approximately 43.7% of the Hg in the wastewater was removed.

Immunogenicity and protective efficacy of orally administered recombinant Lactobacillus plantarum expressing VP2 protein against IBDV in chicken

AIM

To develop an effective oral vaccine against the very virulent infectious bursal disease virus (vvIBDV), we generated two recombinant Lactobacillus plantarum strains (pPG612-VP2/LP and pPG612-T7g10-VP2/LP, which carried the T7g10 translational enhancer) that displayed the VP2 protein on the surface, and compared the humoral and cellular immune responses against vvIBDV in chickens.

METHODS AND RESULTS

We genetically engineered the L. plantarum strains pPG612-VP2/LP and pPG612-T7g10-VP2/LP constitutively expressing the VP2 protein of vvIBDV. We found that the T7g10 enhancer efficiently upregulates VP2 expression in pPG612-T7g10-VP2/LP. Orally administered, pPG612-T7g10-VP2/LP exhibited significant levels of protection (87·5%) against vvIBDV in chickens, indicating improved immunogenicity. Chickens in the pPG612-T7g10-VP2/LP group produced higher levels of interferons (IFN-γ) and interleukins (IL-2 and IL-4) than those in the pPG612-VP2/LP group. CD8+ and CD4+ lymphocyte counts indicated greater stimulation in the pPG612-T7g10-VP2/LP group (13·3 and 21·0% respectively) than in the pPG612-VP2/LP group (10·4 and 14·0% respectively). Thus, pPG612-T7g10-VP2/LP could induce strong humoral and cellular immune responses against vvIBDV.

CONCLUSIONS

The recombinant L. plantarum that expresses pPG612-T7g10-VP2 is a promising candidate for oral vaccine development against vvIBDV.

SIGNIFICANCE AND IMPACT OF THE STUDY

The recombinant Lactobacillus delivery system provides a promising strategy for vaccine development against vvIBDV in chickens.

Correlation of Antagonistic Regulation of leuO Transcription with the Cellular Levels of BglJ-RcsB and LeuO in Escherichia coli

LeuO is a conserved and pleiotropic transcription regulator, antagonist of the nucleoid-associated silencer protein H-NS, and important for pathogenicity and multidrug resistance in Enterobacteriaceae. Regulation of transcription of the leuO gene is complex. It is silenced by H-NS and its paralog StpA, and it is autoregulated. In addition, in Escherichia coli leuO is antagonistically regulated by the heterodimeric transcription regulator BglJ-RcsB and by LeuO. BglJ-RcsB activates leuO, while LeuO inhibits activation by BglJ-RcsB. Furthermore, LeuO activates expression of bglJ, which is likewise H-NS repressed. Mutual activation of leuO and bglJ resembles a double-positive feedback network, which theoretically can result in bi-stability and heterogeneity, or be maintained in a stable OFF or ON states by an additional signal. Here we performed quantitative and single-cell expression analyses to address the antagonistic regulation and feedback control of leuO transcription by BglJ-RcsB and LeuO using a leuO promoter mVenus reporter fusion and finely tunable bglJ and leuO expression plasmids. The data revealed uniform regulation of leuO expression in the population that correlates with the relative cellular concentration of BglJ and LeuO. The data are in agreement with a straightforward model of antagonistic regulation of leuO expression by the two regulators, LeuO and BglJ-RcsB, by independent mechanisms. Further, the data suggest that at standard laboratory growth conditions feedback regulation of leuO is of minor relevance and that silencing of leuO and bglJ by H-NS (and StpA) keeps these loci in the OFF state.

Pseudomonas putida as a platform for the synthesis of aromatic compounds

Aromatic compounds such as l-phenylalanine, 2-phenylethanol and trans-cinnamate are aromatic compounds of industrial interest. Current trends support replacement of chemical synthesis of these compounds by 'green' alternatives produced in microbial cell factories. The solvent-tolerant Pseudomonas putida DOT-T1E strain was genetically modified to produce up to 1 g l-1 of l-phenylalanine. In order to engineer this strain, we carried out the following stepwise process: (1) we selected random mutants that are resistant to toxic phenylalanine analogues; (2) we then deleted up to five genes belonging to phenylalanine metabolism pathways, which greatly diminished the internal metabolism of phenylalanine; and (3) in these mutants, we overexpressed the pheAfbr gene, which encodes a recombinant variant of PheA that is insensitive to feedback inhibition by phenylalanine. Furthermore, by introducing new genes, we were able to further extend the diversity of compounds produced. Introduction of histidinol phosphate transferase (PP_0967), phenylpyruvate decarboxylase (kdc) and an alcohol dehydrogenase (adh) enabled the strain to produce up to 180 mg l-1 2-phenylethanol. When phenylalanine ammonia lyase (pal) was introduced, the resulting strain produced up to 200 mg l-1 of trans-cinnamate. These results demonstrate that P. putida can serve as a promising microbial cell factory for the production of l-phenylalanine and related compounds.

Gene selection and cloning approaches for co-expression and production of recombinant protein-protein complexes

Multiprotein complexes play essential roles in all cells and X-ray crystallography can provide unparalleled insight into their structure and function. Many of these complexes are believed to be sufficiently stable for structural biology studies, but the production of protein-protein complexes using recombinant technologies is still labor-intensive. We have explored several strategies for the identification and cloning of heterodimers and heterotrimers that are compatible with the high-throughput (HTP) structural biology pipeline developed for single proteins. Two approaches are presented and compared which resulted in co-expression of paired genes from a single expression vector. Native operons encoding predicted interacting proteins were selected from a repertoire of genomes, and cloned directly to expression vector. In an alternative approach, Helicobacter pylori proteins predicted to interact strongly were cloned, each associated with translational control elements, then linked into an artificial operon. Proteins were then expressed and purified by standard HTP protocols, resulting to date in the structure determination of two H. pylori complexes.

Backbone circularization of Bacillus subtilis family 11 xylanase increases its thermostability and its resistance against aggregation

While using a serine (S) as linker for circularization increases the thermostability, a longer linker (RGKCWE) leads to reduced aggregation after heat shock at elevated temperatures.

The delta domain of the HK97 major capsid protein is essential for assembly

The 102 residue N-terminal extension of the HK97 major capsid protein, the delta domain, is normally present during the assembly of immature HK97 procapsids, but it is removed during maturation like well-known internal scaffolding proteins of other tailed phages and herpesviruses. The delta domain also shares other unusual properties usually found in other viral and phage scaffolding proteins, including its location on the inside of the capsid, a high predicted and measured α-helical content, and an additional prediction for the ability to form parallel coiled-coils. Viral scaffolding proteins are essential for capsid assembly and phage viability, so we tested whether the HK97 delta domain was essential for capsid assembly. We studied the effects of deleting all or parts of the delta domain on capsid assembly and on complementation of capsid-protein-defective phage, and our results demonstrate that the delta domain is required for HK97 capsid assembly.

The PURE system for protein production

In the field of molecular biology or biochemistry, preparation and use of purified proteins involved in a certain biological system is crucial for understanding their mechanisms and functions in cells or organisms. The recent progress in a cell-free translation system allows us to prepare proteins in a test tube directly from cDNAs that encode the amino acid sequences. The use of the reconstituted cell-free translation system termed PURE (Protein synthesis Using Recombinant Elements) for these purposes is effective in several applications. Here we describe methods of recombinant protein expression using the PURE system for molecular biological or biochemical studies.

Translation enhancer improves the ribosome liberation from translation initiation

For translation initiation in bacteria, the Shine-Dalgarno (SD) and anti-SD sequence of the 30S subunit play key roles for specific interactions between ribosomes and mRNAs to determine the exact position of the translation initiation region. However, ribosomes also must dissociate from the translation initiation region to slide toward the downstream sequence during mRNA translation. Translation enhancers upstream of the SD sequences of mRNAs, which likely contribute to a direct interaction with ribosome protein S1, enhance the yields of protein biosynthesis. Nevertheless, the mechanism of the effect of translation enhancers to initiate the translation is still unknown. In this paper, we investigated the effects of the SD and enhancer sequences on the binding kinetics of the 30S ribosomal subunits to mRNAs and their translation efficiencies. mRNAs with both the SD and translation enhancers promoted the amount of protein synthesis but destabilized the interaction between the 30S subunit and mRNA by increasing the dissociation rate constant (koff) of the 30S subunit. Based on a model for kinetic parameters, a 16-fold translation efficiency could be achieved by introducing a tandem repeat of adenine sequences (A20) between the SD and translation enhancer sequences. Considering the results of this study, translation enhancers with an SD sequence regulate ribosomal liberation from translation initiation to determine the translation efficiency of the downstream coding region.

How to achieve high-level expression of microbial enzymes: strategies and perspectives

Microbial enzymes have been used in a large number of fields, such as chemical, agricultural and biopharmaceutical industries. The enzyme production rate and yield are the main factors to consider when choosing the appropriate expression system for the production of recombinant proteins. Recombinant enzymes have been expressed in bacteria (e.g., Escherichia coli, Bacillus and lactic acid bacteria), filamentous fungi (e.g., Aspergillus) and yeasts (e.g., Pichia pastoris). The favorable and very advantageous characteristics of these species have resulted in an increasing number of biotechnological applications. Bacterial hosts (e.g., E. coli) can be used to quickly and easily overexpress recombinant enzymes; however, bacterial systems cannot express very large proteins and proteins that require post-translational modifications. The main bacterial expression hosts, with the exception of lactic acid bacteria and filamentous fungi, can produce several toxins which are not compatible with the expression of recombinant enzymes in food and drugs. However, due to the multiplicity of the physiological impacts arising from high-level expression of genes encoding the enzymes and expression hosts, the goal of overproduction can hardly be achieved, and therefore, the yield of recombinant enzymes is limited. In this review, the recent strategies used for the high-level expression of microbial enzymes in the hosts mentioned above are summarized and the prospects are also discussed. We hope this review will contribute to the development of the enzyme-related research field.

Minimal effect of gene clustering on expression in Escherichia coli

Genes that interact or function together are often clustered in bacterial genomes, and it has been proposed that this clustering may affect gene expression. In this study, we directly compared gene expression in nonclustered arrangements and in three common clustered arrangements (codirectional, divergent, and operon) using synthetic circuits in Escherichia coli. We found that gene clustering had minimal effects on gene expression. Specifically, gene clustering did not alter constitutive expression levels or stochastic fluctuations in expression ("expression noise"). Remarkably, the expression of two genes that share the same chromosome position with the same promoter (operon) or with separate promoters (codirectional and divergent arrangements) was not significantly more correlated than genes at different chromosome positions (nonclustered arrangements). The only observed effect of clustering was increased transcription factor binding in codirectional and divergent gene arrangements due to DNA looping, but this is not a specific feature of clustering. In summary, we demonstrate that gene clustering is not a general modulator of gene expression, and therefore any effects of clustering are likely to occur only with specific genes or under certain conditions.

Robust translation of the nucleoid protein Fis requires a remote upstream AU element and is enhanced by RNA secondary structure

Synthesis of the Fis nucleoid protein rapidly increases in response to nutrient upshifts, and Fis is one of the most abundant DNA binding proteins in Escherichia coli under nutrient-rich growth conditions. Previous work has shown that control of Fis synthesis occurs at transcription initiation of the dusB-fis operon. We show here that while translation of the dihydrouridine synthase gene dusB is low, unusual mechanisms operate to enable robust translation of fis. At least two RNA sequence elements located within the dusB coding region are responsible for high fis translation. The most important is an AU element centered 35 nucleotides (nt) upstream of the fis AUG, which may function as a binding site for ribosomal protein S1. In addition, a 44-nt segment located upstream of the AU element and predicted to form a stem-loop secondary structure plays a prominent role in enhancing fis translation. On the other hand, mutations close to the AUG, including over a potential Shine-Dalgarno sequence, have little effect on Fis protein levels. The AU element and stem-loop regions are phylogenetically conserved within dusB-fis operons of representative enteric bacteria.

An efficient design strategy for a whole-cell biosensor based on engineered ribosome binding sequences

In prokaryotes, the ribosome binding sequence (RBS), located in the 5' untranslated region (5' UTR) of an mRNA, plays a critical role in enhancing mRNA translation and stability. To evaluate the effect of the RBS on the sensitivity and signal intensity of an environmental whole-cell biosensor, three Escherichia coli-based biosensors that respond to benzene, toluene, ethylbenzene, and the xylenes (BTEX) were constructed; the three biosensors have the same Pu promoter and xylR regulator from the Pseudomonas putida TOL plasmid but differ in the engineered RBS in their reporter genes. The results from time and dose-dependent induction of luminescence activity by 2-chlorotoluene showed that the BTEX-SE and BTEX-SD biosensors with engineered RBS had signal intensities approximately 10-35 times higher than the primary BTEX-W biosensor. The limits of detection (LOD) of the BTEX-SE and BTEX-SD biosensors were also significantly lower than the LOD of the BTEX-W biosensor (20 ± 5 μmol L(-1) and 25 ± 5 μmol L(-1) vs. 120 ± 10 μmol L(-1)). Moreover, the BTEX-SE and BTEX-SD biosensors responded three times more rapidly to the analytes. These results suggest that rationally designed RBS in the 5' UTR of a reporter gene may be a promising strategy for increasing the sensitivity, signal intensity, and response speed of whole-cell biosensors.

Characterization of mercury bioremediation by transgenic bacteria expressing metallothionein and polyphosphate kinase

Background

The use of transgenic bacteria has been proposed as a suitable alternative for mercury remediation. Ideally, mercury would be sequestered by metal-scavenging agents inside transgenic bacteria for subsequent retrieval. So far, this approach has produced limited protection and accumulation. We report here the development of a transgenic system that effectively expresses metallothionein (mt-1) and polyphosphate kinase (ppk) genes in bacteria in order to provide high mercury resistance and accumulation.

Results

In this study, bacterial transformation with transcriptional and translational enhanced vectors designed for the expression of metallothionein and polyphosphate kinase provided high transgene transcript levels independent of the gene being expressed. Expression of polyphosphate kinase and metallothionein in transgenic bacteria provided high resistance to mercury, up to 80 μM and 120 μM, respectively. Here we show for the first time that metallothionein can be efficiently expressed in bacteria without being fused to a carrier protein to enhance mercury bioremediation. Cold vapor atomic absorption spectrometry analyzes revealed that the mt-1 transgenic bacteria accumulated up to 100.2 ± 17.6 μM of mercury from media containing 120 μM Hg. The extent of mercury remediation was such that the contaminated media remediated by the mt-1 transgenic bacteria supported the growth of untransformed bacteria. Cell aggregation, precipitation and color changes were visually observed in mt-1 and ppk transgenic bacteria when these cells were grown in high mercury concentrations.

Conclusion

The transgenic bacterial system described in this study presents a viable technology for mercury bioremediation from liquid matrices because it provides high mercury resistance and accumulation while inhibiting elemental mercury volatilization. This is the first report that shows that metallothionein expression provides mercury resistance and accumulation in recombinant bacteria. The high accumulation of mercury in the transgenic cells could present the possibility of retrieving the accumulated mercury for further industrial applications.

The interplay of mRNA stimulatory signals required for AUU-mediated initiation and programmed -1 ribosomal frameshifting in decoding of transposable element IS911

The IS911 bacterial transposable element uses -1 programmed translational frameshifting to generate the protein required for its mobility: translation initiated in one gene (orfA) shifts to the -1 frame and continues in a second overlapping gene (orfB), thus generating the OrfAB transposase. The A-AAA-AAG frameshift site of IS911 is flanked by two stimulatory elements, an upstream Shine-Dalgarno sequence and a downstream stem-loop. We show here that, while they can act independently, these stimulators have a synergistic effect when combined. Mutagenic analyses revealed features of the complex stem-loop that make it a low-efficiency stimulator. They also revealed the dual role of the upstream Shine-Dalgarno sequence as (i) a stimulator of frameshifting, by itself more potent than the stem-loop, and (ii) a mandatory determinant of initiation of OrfB protein synthesis on an AUU codon directly preceding the A6G motif. Both roles rely on transient base pairing of the Shine-Dalgarno sequence with the 3' end of 16S rRNA. Because of its effect on frameshifting, the Shine-Dalgarno sequence is an important determinant of the level of transposase in IS911-containing cells, and hence of the frequency of transposition.

Overexpression of mouse estrogen receptor-β decreases but its transactivation and ligand binding domains increase the growth characteristics of E. coli

Escherichia coli is one of the most common and widely used prokaryotic hosts for the expression of recombinant proteins. The overexpression of recombinant proteins occasionally increases bacterial growth but sometimes reduces it and becomes lethal to the host cells. Here, we report the overexpression of mouse ER-β and its domains in the prokaryotic expression system and its opposite effect on the growth characteristics of E. coli. ER-β protein was immunologically detected as a 53 kDa his-tag protein in the pellet of the bacterial lysate. Its overexpression, as reflected by the total protein content and expression pattern, resulted in the decrease of bacterial growth. However, the overexpression of ER-β transactivation domain (TAD) using pIVEX and ligand binding domain (LBD) using pRSETA in E. coli BL21 (DE3) show opposite pattern. TAD was immunologically detected as 20 kDa and LBD as 22 kDa protein in the supernatant of the bacterial lysate and their overexpression increased the bacterial growth.

In vitro transcription and translation inhibition via DNA functionalized gold nanoparticles

The use of gold nanoparticles (AuNPs) has been gaining momentum as vectors for gene silencing strategies, combining the AuNPs' ease of functionalization with DNA and/or siRNA, high loading capacity and fast uptake by target cells. Here, we used AuNP functionalized with thiolated oligonucleotides to specifically inhibit transcription in vitro, demonstrating the synergetic effect between AuNPs and a specific antisense sequence that blocks the T7 promoter region. Also, AuNPs efficiently protect the antisense oligonucleotide against nuclease degradation, which can thus retain its inhibitory potential. In addition, we demonstrate that AuNPs functionalized with a thiolated oligonucleotide complementary to the ribosome binding site and the start codon, effectively shut down in vitro translation. Together, these two approaches can provide for a simple yet robust experimental set up to test for efficient gene silencing of AuNP-DNA conjugates. What is more, these results show that appropriate functionalization of AuNPs can be used as a dual targeting approach to an enhanced control of gene expression-inhibition of both transcription and translation.

PURE technology

The Escherichia coli-based reconstituted cell-free protein synthesis system, which we named the PURE (Protein synthesis Using Recombinant Elements) system, provides several advantages compared with the conventional cell-extract-based system. Stability of RNA or protein is highly improved because of the lack of harmful degradation enzymes. The system can be easily engineered according to purposes or the proteins to be synthesized, by manipulating the components in the system. In this chapter, we describe the construction and exploitation of the PURE system. Methods for preparing and assembling the components composing the PURE system for the protein synthesis reaction are shown.