High-level fed-batch fermentative expression of an engineered Staphylococcal protein A based ligand in E. coli: purification and characterization

Accelerated Adaptive Laboratory Evolution by Automated Repeated Batch Processes in Parallelized Bioreactors

Adaptive laboratory evolution (ALE) is a valuable complementary tool for modern strain development. Insights from ALE experiments enable the improvement of microbial cell factories regarding the growth rate and substrate utilization, among others. Most ALE experiments are conducted by serial passaging, a method that involves large amounts of repetitive manual labor and comes with inherent experimental design flaws. The acquisition of meaningful and reliable process data is a burdensome task and is often undervalued and neglected, but also unfeasible in shake flask experiments due to technical limitations. Some of these limitations are alleviated by emerging automated ALE methods on the μL and mL scale. A novel approach to conducting ALE experiments is described that is faster and more efficient than previously used methods. The conventional shake flask approach was translated to a parallelized, L scale stirred-tank bioreactor system that runs controlled, automated, repeated batch processes. The method was validated with a growth optimization experiment of E. coli K-12 MG1655 grown with glycerol minimal media as a benchmark. Off-gas analysis enables the continuous estimation of the biomass concentration and growth rate using a black-box model based on first principles (soft sensor). The proposed method led to the same stable growth rates of E. coli with the non-native carbon source glycerol 9.4 times faster than the traditional manual approach with serial passaging in uncontrolled shake flasks and 3.6 times faster than an automated approach on the mL scale. Furthermore, it is shown that the cumulative number of cell divisions (CCD) alone is not a suitable timescale for measuring and comparing evolutionary progress.

How to Perform a Microfluidic Cultivation Experiment—A Guideline to Success

As a result of the steadily ongoing development of microfluidic cultivation (MC) devices, a plethora of setups is used in biological laboratories for the cultivation and analysis of different organisms. Because of their biocompatibility and ease of fabrication, polydimethylsiloxane (PDMS)-glass-based devices are most prominent. Especially the successful and reproducible cultivation of cells in microfluidic systems, ranging from bacteria over algae and fungi to mammalians, is a fundamental step for further quantitative biological analysis. In combination with live-cell imaging, MC devices allow the cultivation of small cell clusters (or even single cells) under defined environmental conditions and with high spatio-temporal resolution. Yet, most setups in use are custom made and only few standardised setups are available, making trouble-free application and inter-laboratory transfer tricky. Therefore, we provide a guideline to overcome the most frequently occurring challenges during a MC experiment to allow untrained users to learn the application of continuous-flow-based MC devices. By giving a concise overview of the respective workflow, we give the reader a general understanding of the whole procedure and its most common pitfalls. Additionally, we complement the listing of challenges with solutions to overcome these hurdles. On selected case studies, covering successful and reproducible growth of cells in MC devices, we demonstrate detailed solutions to solve occurring challenges as a blueprint for further troubleshooting. Since developer and end-user of MC devices are often different persons, we believe that our guideline will help to enhance a broader applicability of MC in the field of life science and eventually promote the ongoing advancement of MC.

Control algorithms and strategies of feeding for fed-batch fermentation of Escherichia coli: a review of 40 years of experience

Fed-batch cultivation is a well-known type of submerged fermentation that is frequently used in manufacture of recombinant proteins and various kinds of enzymes, owing to its ability to produce products with high concentrations and high efficiency. In fed-batch culture, several issues must be considered; most of them are also presented in batch culture. However, feed flow rate calculation only corresponds to fed-batch fermentation and its value has a significant impact on productivity, efficiency, final concentration of product, formation of by-products, and viscosity of the culture. From this background, the present review article is an effort to gather the information on feeding strategies for fed-batch cultivation of Escherichia coli, which is a well-known microorganism in the production of recombinant proteins and industrial enzymes, especially for therapeutic applications. Moreover, this review is an aid to comprehend and compare the fundamental concept of different feeding strategies and their advantages and drawbacks.

Peptide binding to metal oxide nanoparticles

Magnetic metal oxide nanoparticles demonstrate great applicability in several fields such as biotechnology, medicine and catalysis. A stable, magnetic and low-cost material, nanoscale magnetite, is an interesting adsorbent for protein purification. Downstream processing can account for up to 80% of the total production costs in biotechnological production. As such, the development of new innovative separation methods can be regarded as highly profitable. While short peptide sequences can be used as specific affinity tags for functionalised adsorber surfaces, they need expensive affinity ligands on the particle surface for adsorption. In order to identify peptide tags for several non-functionalised inorganic surfaces, different binding conditions to iron oxide nanoparticles are evaluated. Therefore, magnetite nanoparticles in a range of 5-20 nm were synthesised with a co-precipitation method. Zeta potential measurements indicated an amphiphilic surface with an isoelectric point in the neutral pH region. Glutamic acid-based homo-peptides were used as affinity peptides for the magnetite nanoparticles. We demonstrate a dependence of the binding affinity of the peptides on pH and buffer ions in two different experimental set-ups. The nature of surface coordination for glutamic acid-based peptides can be demonstrated with different spectroscopic approaches such as infrared spectroscopy (IR), Raman spectroscopy and circular dichroism spectroscopy (CD). We want to emphasise the importance of physicochemical properties such as surface energy, polarity, morphology and charge. These parameters, which are dependent on the environmental conditions, play a crucial role in peptide interactions with iron oxide surfaces. The understanding of the adsorption of simple biomolecules on nanoscale metal oxide surfaces also represents the key to the even more complex interactions of proteins at the bio-nano interface. From the identification of interaction patterns and an understanding of the adsorption of these peptides, the up-scaling to tagged model proteins facilitates the possibility of an industrial magnetic separation process and might therefore reduce time and costs in purification processes.

A comprehensive review on staphylococcal protein A (SpA): Its production and applications

The Staphylococcus aureus protein A (SpA) can be obtained through the culture of wild-type S. aureus and also as a recombinant protein in safe bacterial hosts. Several methods have been used to purify SpA among which ion-exchange chromatography, affinity chromatography, gel filtration, and per aqueous liquid chromatography (PALC) are common. SpA has a wide range of biochemical, biotechnological, and medical applications and is most commonly used in test methods such as immunoprecipitation, enzyme-linked immunosorbent assay, and Western blotting. SpA has also been widely utilized in pharmaceutical applications to bind to immune complexes and serum immunoglobulins. SpA also directly binds to the B-cells preventing initiation of infectious diseases as well as having a role in the development of various autoimmune diseases. This review considers different applications of SpA in biotechnology and its novel clinical application for effective treatment of autoimmune diseases. It also discusses various strategies for expression and purification of the SpA including types of column chromatography that are commonly used in protein purification and developing SpA surface display technologies. Finally, this review highlights the potential and novel applications of SpA immobilization, SpA typing, protein engineering for further development of immunological and biochemical research, and also application of SpA as a diagnostic biosensor.

Preparation of kenaf stem hemicellulosic hydrolysate and its fermentability in microbial production of xylitol by Escherichia coli BL21

Kenaf (Hibiscus cannabinus L.), a potential fibre crop with a desirably high growth rate, could serve as a sustainable feedstock in the production of xylitol. In this work, the extraction of soluble products of kenaf through dilute nitric-acid hydrolysis was elucidated with respect to three parameters, namely temperature, residence time, and acid concentration. The study will assist in evaluating the performance in terms of xylose recovery. The result point out that the maximum xylose yield of 30.7 g per 100 g of dry kenaf was attained from 2% (v/v) HNO₃ at 130 °C for 60 min. The detoxified hydrolysate was incorporated as the primary carbon source for subsequent fermentation by recombinant Escherichia coli and the performance of strain on five different semi-synthetic media on xylitol production were evaluated herein. Among these media, batch cultivation in a basal salt medium (BSM) afforded the highest xylitol yield of 0.35 g/g based on xylose consumption, which corresponded to 92.8% substrate utilization after 38 h. Subsequently, fermentation by E. coli in the xylose-based kenaf hydrolysate supplemented with BSM resulting in 6.8 g/L xylitol which corresponding to xylitol yield of 0.38 g/g. These findings suggested that the use of kenaf as the fermentation feedstock could be advantageous for the development of sustainable xylitol production.

An engineered Staphylococcal Protein A based ligand: Production, characterization and potential application for the capture of Immunoglobulin and Fc-fusion proteins

In antibody purification processes, affinity chromatography has been used with Staphylococcus aureus protein A (SpA) as the main ligand. In this work, we present a novel Staphylococcal Protein A (AviPure thereafter), a synthetic ligand analogue based on native SpA B domain, with a molecular weight of approximately 14 kDa. The binding affinity of mAbs to AviPure was evaluated using Surface Plasmon Resonance (SPR) and affinity chromatography methods. The equilibrium dissociation constant (K_D) between the AviPure and mAbs was systematically measured using 1:1 (Langmuir) model and found to be 4.7 × 10^-8 M, with constant of dissociation at k_d ≤ 1.0 × 10^-3 s^-1 and k_a being 3.1 × 10⁴ M^-1 s^-1. When immobilized on Sepharose, the AviPure ligand density was 429 nmol/g moist weight resin and was able to effectively bind immunoglobulin and Fc fragment samples with higher affinity and the most effective flow rate when using ligand - Sepharose beads was at 75 cm/h giving the dynamic binding capacity of 53 mg/mL and 91% recovery of IgG. Suitable ligands used in affinity purification should have a K_D ≤ 10^-6 M and a dissociation rate (k_a) averaging 10^-3 M^-1 s^-1 with the k_d ranging between 10³ - 10⁸ M^-1. Therefore, the AviPure ligand can be used as an alternative to the standard protein A ligand in the purification of mAbs and Fc-fused proteins.

Milligram scale production of potent recombinant small interfering RNAs in Escherichia coli

Small interfering RNAs (siRNAs) are invaluable research tools for studying gene functions in mammalian cells. siRNAs are mainly produced by chemical synthesis or by enzymatic digestion of double-stranded RNA (dsRNA) produced in vitro. Recently, bacterial cells, engineered with ectopic plant viral siRNA binding protein p19, have enabled the production of "recombinant" siRNAs (pro-siRNAs). Here, we describe an optimized methodology for the production of milligram amount of highly potent recombinant pro-siRNAs from Escherichia coli cells. We first optimized bacterial culture medium and tested new designs of pro-siRNA production plasmid. Through the exploration of multiple pro-siRNA related factors, including the expression of p19 protein, (dsRNA) generation method, and the level of RNase III, we developed an optimal pro-siRNA production plasmid. Together with a high-cell density fed-batch fermentation method in a bioreactor, we have achieved a yield of ~10 mg purified pro-siRNA per liter of bacterial culture. The pro-siRNAs produced by the optimized method can achieve high efficiency of gene silencing when used at low nanomolar concentrations. This new method enables fast, economical, and renewable production of pure and highly potent bioengineered pro-siRNAs at the milligram level. Our study also provides important insights into the strategies for optimizing the production of RNA products in bacteria, which is an under-explored field.

Human heart failure biomarker immunosensor based on excessively tilted fiber gratings

A label-free immunosensor platform based on excessively tilted fiber gratings (Ex-TFGs) was developed for highly specific and fast detection of human N-terminal pro-B-type natriuretic peptide (NT-proBNP), which is considered a powerful biomarker for prognosis and risk stratification of heart failure (HF). High-purity anti-NT-proBNP monoclonal antibodies (MAbs) prepared in our laboratory were immobilized on fiber surface through the staphylococcal protein A (SPA) method for subsequent specific binding of the targeted NT-proBNP. Utilizing fiber optic grating demodulation system (FOGDS), immunoassays were carried out in vitro by monitoring the resonance wavelength shift of Ex-TFG biosensor with immobilized anti-NT-proBNP MAbs. Lowest detectable concentration of ~0.5ng/mL for NT-proBNP was obtained, and average sensitivity for NT-proBNP at a concentration range of 0~1.0 ng/mL was approximately 45.967 pm/(ng/mL). Several human serum samples were assessed by the proposed Ex-TFG biomarker sensor, with high specificity for NT-proBNP, indicating potential application in early diagnosing patients with acute HF symptoms.

Life-history strategies and carbon metabolism gene dosage in the Nakaseomyces yeasts

The Nakaseomyces clade consists of a group of six hemiascomyceteous yeasts (Candida glabrata, Nakaseomyces delphensis, C. nivarensis, C. bracarensis, C. castelli, N. bacillisporus), phylogenetically close to the yeast Saccharomyces cerevisiae, their representative being the well-known pathogenic yeast C. glabrata. Four species had been previously examined for their carbon assimilation properties and found to have similar properties to S. cerevisiae (repression of respiration in high glucose-i.e. Crabtree positivity-and being a facultative anaerobe). We examined here the complete set of the six species for their carbon metabolic gene content. We also measured different metabolic and life-history traits (glucose consumption rate, population growth rate, carrying capacity, cell size, cell and biomass yield). We observed deviations from the glycolytic gene redundancy observed in S. cerevisiae presumed to be an important property for the Crabtree positivity, especially for the two species C. castelli and N. bacillisporus which frequently have only one gene copy, but different life strategies. Therefore, we show that the decrease in carbon metabolic gene copy cannot be simply associated with a reduction of glucose consumption rate and can be counterbalanced by other beneficial genetic variations.