Extractive cultivation of recombinant Escherichia coli using aqueous two phase systems for production and separation of extracellular xylanase

An integrative approach to improving the biocatalytic reactions of whole cells expressing recombinant enzymes

Biotransformation is a selective, stereospecific, efficient, and environment friendly method, compared to chemical synthesis, and a feasible tool for industrial and pharmaceutical applications. The design of biocatalysts using enzyme engineering and metabolic engineering tools has been widely reviewed. However, less importance has been given to the biocatalytic reaction of whole cells expressing recombinant enzymes. Along with the remarkable development of biotechnology tools, a variety of techniques have been applied to improve the biocatalytic reaction of whole cell biotransformation. In this review, techniques related to the biocatalytic reaction are examined, reorganized, and summarized via an integrative approach. Moreover, equilibrium-shifted biotransformation is reviewed for the first time.

Enzymatic Hydrolysis of Sugarcane Bagasse in Aqueous Two-Phase Systems (ATPS): Exploration and Conceptual Process Design

The enzymatic conversion of lignocellulosic material to sugars can provide a carbon source for the production of energy (fuels) and a wide range of renewable products. However, the efficiency of this conversion is impaired due to product (sugar) inhibition. Even though several studies investigate how to overcome this challenge, concepts on the process to conduct the hydrolysis are still scarce in literature. Aqueous two-phase systems (ATPS) can be applied to design an extractive reaction due to their capacity to partition solutes to different phases in such a system. This work presents strategies on how to conduct extractive enzymatic hydrolysis in ATPS and how to explore the experimental results in order to design a feasible process. While only a limited number of ATPS was explored, the methods and strategies described could easily be applied to any further ATPS to be explored. We studied two promising ATPS as a subset of a previously high throughput screened large set of ATPS, providing two configurations of processes having the reaction in either the top phase or in the bottom phase. Enzymatic hydrolysis in these ATPS was performed to evaluate the partitioning of the substrate and the influence of solute partitioning on conversion. Because ATPS are able to partition inhibitors (sugar) between the phases, the conversion rate can be maintained. However, phase forming components should be selected to preserve the enzymatic activity. The experimental results presented here contribute to a feasible ATPS-based conceptual process design for the enzymatic conversion of lignocellulosic material.

Expansion of bone marrow-derived human mesenchymal stem/stromal cells (hMSCs) using a two-phase liquid/liquid system

BACKGROUND

Human mesenchymal stem/stromal cells (hMSCs) are at the forefront of regenerative medicine applications due to their relatively easy isolation and availability in adults, potential to differentiate and to secrete a range of trophic factors that could determine specialised tissue regeneration. To date, hMSCs have been successfully cultured in vitro on substrates such as polystyrene dishes (TCPS) or microcarriers. However, hMSC sub-cultivation and harvest typically employs proteolytic enzymes that act by cleaving important cell membrane proteins resulting in long-term cell damage. In a process where the cells themselves are the product, a non-enzymatic and non-damaging harvesting approach is desirable.

RESULTS

An alternative system for hMSC expansion and subsequent non-enzymatic harvest was investigated here. A liquid/liquid two-phase system was proposed, comprising a selected perfluorocarbon (FC40) and growth medium (DMEM). The cells exhibited similar cell morphologies compared with TCPS. Moreover, they retained their identity and differentiation potential post-expansion and post-harvest. Further, no significant difference was found when culturing hMSCs in the culture systems prepared with either fresh or recycled FC40 perfluorocarbon.

CONCLUSIONS

These findings make the FC40/DMEM system an attractive alternative for traditional cell culture substrates due to their ease of cell recovery and recyclability, the latter impacting on overall process costs. © 2017 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Thermoseparating aqueous two-phase systems: Recent trends and mechanisms

Having the benefits of being environmentally friendly, providing a mild environment for bioseparation, and scalability, aqueous two-phase systems (ATPSs) have increasingly caught the attention of industry and researchers for their application in the isolation and recovery of bioproducts. The limitations of conventional ATPSs give rise to the development of temperature-induced ATPSs that have distinctive thermoseparating properties and easy recyclability. This review starts with a brief introduction to thermoseparating ATPSs, including its history, unique characteristics and advantages, and lastly, key factors that influence partitioning. The underlying mechanism of temperature-induced ATPSs is covered together with a summary of recent applications. Thermoseparating ATPSs have been proven as a solution to the demand for economically favorable and environmentally friendly industrial-scale bioextraction and purification techniques.

Extractive fermentation for improved production and recovery of lipase derived from Burkholderia cepacia using a thermoseparating polymer in aqueous two-phase systems

An extractive fermentation technique was developed using a thermoseparating reagent to form a two-phase system for simultaneous cell cultivation and downstream processing of extracellular Burkholderia cepacia lipase. A 10% (w/w) solution of ethylene oxide-propylene oxide (EOPO) with a molecular mass of 3900 g/mol and pH 8.5, a 200 rpm speed, and 30 °C were selected as the optimal conditions for lipase production (55 U/ml). Repetitive batch fermentation was performed by continuous replacement of the top phase every 24h, which resulted in an average cell growth mass of 4.7 g/L for 10 extractive batches over 240 h. In scaling-up the process, a bench-scale bioreactor was tested under the conditions that had been optimized in flasks. The production rate and recovery yield were higher in the bioreactor compared to fermentation performed in flasks.

Engineering hyperthermostability into a GH11 xylanase is mediated by subtle changes to protein structure

Understanding the structural basis for protein thermostability is of considerable biological and biotechnological importance as exemplified by the industrial use of xylanases at elevated temperatures in the paper pulp and animal feed sectors. Here we have used directed protein evolution to generate hyperthermostable variants of a thermophilic GH11 xylanase, EvXyn11. The Gene Site Saturation Mutagenesis (GSSM) methodology employed assesses the influence on thermostability of all possible amino acid substitutions at each position in the primary structure of the target protein. The 15 most thermostable mutants, which generally clustered in the N-terminal region of the enzyme, had melting temperatures (Tm) 1-8 degrees C higher than the parent protein. Screening of a combinatorial library of the single mutants identified a hyperthermostable variant, EvXyn11TS, containing seven mutations. EvXyn11TS had a Tm approximately 25 degrees C higher than the parent enzyme while displaying catalytic properties that were similar to EvXyn11. The crystal structures of EvXyn11 and EvXyn11TS revealed an absence of substantial changes to identifiable intramolecular interactions. The only explicable mutations are T13F, which increases hydrophobic interactions, and S9P that apparently locks the conformation of a surface loop. This report shows that the molecular basis for the increased thermostability is extraordinarily subtle and points to the requirement for new tools to interrogate protein folding at non-ambient temperatures.

Research and application of microbial enzymes--India's contribution

Enzymes have attracted the attention of scientists world over due to their wide range of physiological, analytical and industrial applications. Although enzymes have been isolated, purified and studied from microbial, animal and plant sources, microorganisms represent the most common source of enzymes due to their broad biochemical diversity, feasibility of mass culture and ease of genetic manipulation. With the advent of molecular biology techniques, a number of genes of industrially important enzymes has been cloned and expressed in order to improve the production of enzymes, substrate utilization and other commercially useful properties. Special attention has been focused on enzymes isolated from thermophiles due to their inherent stability and industrial applications. In addition, a variety of methods have been employed to modify enzymes for their industrial usage including strain improvement, chemical modifications, modification of reaction environment, immobilization and protein engineering. A wide range of applications of enzymes in different bioprocess industries is discussed.

In situ product removal (ISPR) in whole cell biotechnology during the last twenty years

This review sums up the activity in the field of in situ product removal in whole cell bioprocesses over the last 20 years. It gives a complete summary of ISPR operations with microbial cells and cites a series of interesting ISPR applications in plant and animal cell technology. All the ISPR projects with microbial cells are categorized according to their products, their ISPR techniques, and their applied configurations of the ISPR set-up. Research on ISPR application has primarily increased in the field of microbial production of aromas and organic acids such lactic acid over the last ten years. Apart from the field of de novo formation of bioproducts, ISPR is increasingly applied to microbial bioconversion processes. However, despite of the large number of microbial whole cell ISPR projects (approximately 250), very few processes have been transferred to an industrial scale. The proposed processes have mostly been too complex and consequently not cost effective. Therefore, this review emphasizes that the planning of a successful whole cell ISPR process should not only consider the choice of ISPR technique according to the physicochemical properties of the product, but also the potential configuration of the whole process set-up. Furthermore, additional process aspects, biological and legal constraint need to be considered from the very beginning for the design of an ISPR project. Finally, future trends of new, modified or improved ISPR techniques are given.

Membrane-assisted extractive bioconversions

This chapter summarizes the use of membrane reactors in extractive bioconversions as process integration systems leading to in situ product recovery. Several membrane reactor configurations are analyzed, taking into account the type of bioconversion, biocatalyst type and location (either in the aqueous phase or in the membrane), membrane chemistry and morphology, solvent (extractant) type and its biocompatibility. Modeling of liquid-liquid extractive membrane bioreactors operation is also analyzed considering kinetics and mass-transfer aspects. The chapter includes examples from the authors' laboratory as well as other published in the field. Both enzyme and whole cell-based bioconversions are considered. Relevant aspects related to the solvent (extractant) toxicity and how the membrane could protect the biocatalytic activity are analyzed. Trends in this field are also given.

Electroelution as a simple and fast protein purification method: isolation of an extracellular xylanase from Bacillus sp. CCMI 966

An efficient and simple modified method of electroelution is described that can be used as a time-saving method for eluting multiple protein bands. Provided that the proteins are highly expressed, they can be purified rapidly and without requiring any prior knowledge of the protein characteristics. A xylanase excreted by Bacillus sp. CCMI 966 was purified directly from the polyacrylamide gel. Some of the properties of this enzyme are presented. It had an unusually apparent high molecular mass of 340kDa, as determined by native PAGE. The specific activity of the purified xylanase was 137 U/mg.

Xylanase II from an alkaliphilic thermophilic Bacillus with a distinctly different structure from other xylanases: evolutionary relationship to alkaliphilic xylanases

A 1.0 kilobase gene fragment from the genomic DNA of an alkaliphilic thermophilic Bacillus was found to code for a functional xylanase (XynII). The complete nucleotide sequence including the structural gene and the 5' and 3' flanking sequences of the xylanase gene have been determined. An open reading frame starting from ATG initiator codon comprising 402 nucleotides gave a preprotein of 133 amino acids of calculated molecular mass 14.090 kDa. The occurrence of three potential N-glycosylation sites in XynII gene is a unique feature for a gene of bacterial origin. The stop codon was followed by hairpin loop structures indicating the presence of transcription termination signals. The secondary structure analysis of XynII predicted that the polypeptide was primarily formed of beta-sheets. XynII appeared to be a member of family G/11 of xylanases based on its molecular weight and basic pI (8.0). However, sequence homology revealed similar identity with families 10 and 11 of xylanases. The conserved triad (Val-Val-Xaa, where Xaa is Asn or Asp) was identified only in the xylanases from alkaliphilic organisms. Our results implicate for the first time the concept of convergent evolution for XynII and provide a basis for research in evolutionary relationship among the xylanases from alkaliphilic and neutrophilic organisms.