Bioreactors: Design and Operation

Biodegradation of highly crystallized poly(ethylene terephthalate) through cell surface codisplay of bacterial PETase and hydrophobin

The process of recycling poly(ethylene terephthalate) (PET) remains a major challenge due to the enzymatic degradation of high-crystallinity PET (hcPET). Recently, a bacterial PET-degrading enzyme, PETase, was found to have the ability to degrade the hcPET, but with low enzymatic activity. Here we present an engineered whole-cell biocatalyst to simulate both the adsorption and degradation steps in the enzymatic degradation process of PETase to achieve the efficient degradation of hcPET. Our data shows that the adhesive unit hydrophobin and degradation unit PETase are functionally displayed on the surface of yeast cells. The turnover rate of the whole-cell biocatalyst toward hcPET (crystallinity of 45%) dramatically increases approximately 328.8-fold compared with that of purified PETase at 30 °C. In addition, molecular dynamics simulations explain how the enhanced adhesion can promote the enzymatic degradation of PET. This study demonstrates engineering the whole-cell catalyst is an efficient strategy for biodegradation of PET.

Combining a Genetically Engineered Oxidase with Hydrogen-Bonded Organic Frameworks (HOFs) for Highly Efficient Biocomposites

Enzymes incorporated into hydrogen-bonded organic frameworks (HOFs) via bottom-up synthesis are promising biocomposites for applications in catalysis and sensing. Here, we explored synthetic incorporation of d-amino acid oxidase (DAAO) with the metal-free tetraamidine/tetracarboxylate-based BioHOF-1 in water. N-terminal enzyme fusion with the positively charged module Zbasic2 strongly boosted the loading (2.5-fold; ≈500 mg enzyme gmaterial-1 ) and the specific activity (6.5-fold; 23 U mg-1 ). The DAAO@BioHOF-1 composites showed superior activity with respect to every reported carrier for the same enzyme and excellent stability during catalyst recycling. Further, extension to other enzymes, including cytochrome P450 BM3 (used in the production of high-value oxyfunctionalized compounds), points to the versatility of genetic engineering as a strategy for the preparation of biohybrid systems with unprecedented properties.

Enzymatic Bioreactors: An Electrochemical Perspective

Biocatalysts provide a number of advantages such as high selectivity, the ability to operate under mild reaction conditions and availability from renewable resources that are of interest in the development of bioreactors for applications in the pharmaceutical and other sectors. The use of oxidoreductases in biocatalytic reactors is primarily focused on the use of NAD(P)-dependent enzymes, with the recycling of the cofactor occurring via an additional enzymatic system. The use of electrochemically based systems has been limited. This review focuses on the development of electrochemically based biocatalytic reactors. The mechanisms of mediated and direct electron transfer together with methods of immobilising enzymes are briefly reviewed. The use of electrochemically based batch and flow reactors is reviewed in detail with a focus on recent developments in the use of high surface area electrodes, enzyme engineering and enzyme cascades. A future perspective on electrochemically based bioreactors is presented.

Dynamic Culture Systems and 3D Interfaces Models for Cancer Drugs Testing

The mass use of biological agents for pharmaceutical purposes started with the development and distribution of vaccines, followed by the industrial production of antibiotics. The use of dynamic systems, such as bioreactors, had been already applied in the food industry in fermentation processes and started being used for the development of pharmaceutical agents from this point on. In the last decades, the use of bioreactors and microfluidic systems has been expanded in different fields. The emergence of the tissue engineering led to the development of in vitro models cultured in dynamic systems. This is particularly relevant considering the urgent reduction of the total dependence on animal disease models that is undermining the development of novel drugs, using alternatively human-based models to make the drug discovery process more reliable. The failure out coming from animal models has been more prevalent in certain types of cancer, such as glioblastoma multiform and in high-grade metastatic cancers like bone metastasis of breast or prostatic cancer. The difficulty in obtaining novel drugs for these purposes is mostly linked to the barriers around the tumors, which these bioactive molecules have to overcome to become effective. For that reason, the individualized study of each interface is paramount and is only realistic once applying human-based samples (e.g. cells or tissues) in three-dimensions for in vitro modeling under dynamic conditions. In this chapter, the most recent approaches to model these interfaces in 3D systems will be explored, highlighting their major contributions to the field. In this section, these systems' impact on increased knowledge in relevant aspects of cancer aggressiveness as invasive or motile cellular capacity, or even resistance to chemotherapeutic agents will have particular focus. The last section of this chapter will focus on the integration of the tumor interfaces in dynamic systems, particularly its application on high-throughput drug screening. The industrial translation of such platforms will be discussed, as well as the main upcoming challenges and future perspectives.

Efficient biodegradation of highly crystallized polyethylene terephthalate through cell surface display of bacterial PETase

Polyethylene terephthalate (PET) is one of the most widely used plastics in the world. Accumulation of the discarded PET in the environment is creating a global environmental problem. Recently, a bacterial enzyme named PETase was found to have the novel ability to degrade the highly crystallized PET. However, the enzymatic activity of native PETase is still low limiting its possible use in recycling of PET. In this study, we developed a whole-cell biocatalyst by displaying PETase on the surface of yeast (Pichia pastoris) cell to improve its degradation efficiency. Our data shows that PETase could be functionally displayed on the yeast cell with enhanced pH and thermal stability. The turnover rate of the PETase-displaying yeast whole-cell biocatalyst towards highly crystallized PET dramatically increased about 36-fold compared with that of purified PETase. Furthermore, the whole-cell biocatalyst showed stable turnover rate after seven repeated use and under some chemical/solvent conditions, and its ability to degrade different commercial highly crystallized PET bottles. Our results reveal that PETase-displaying whole-cell biocatalyst affords a promising route for efficient biological recycling of PET.

Multi-stage continuous high cell density culture systems: a review

A multi-stage continuous high cell density culture (MSC-HCDC) system makes it possible to achieve high productivity together with high product titer of many bioproducts. For long-term continuous operation of MSC-HCDC systems, the cell retention time and hydraulic retention time must be decoupled and strains (bacteria, yeast, plant, and animal cells) must be stable. MSC-HCDC systems are suitable for low-value high-volume extracellular products such as fuel ethanol, lactic acid or volatile fatty acids, and high-value products such as monoclonal antibodies as well as intracellular products such as polyhydroxybutyric acid (PHB), microbial lipids or a number of therapeutics. Better understanding of the fermentation kinetics of a specific product and reliable high-density culture methods for the product-generating microorganisms will facilitate timely industrialization of MSC-HCDC systems for products that are currently obtained in fed-batch bioreactors.

Heterotrophic cultures of microalgae: metabolism and potential products

This review analyzes the current state of a specific niche of microalgae cultivation; heterotrophic growth in the dark supported by a carbon source replacing the traditional support of light energy. This unique ability of essentially photosynthetic microorganisms is shared by several species of microalgae. Where possible, heterotrophic growth overcomes major limitations of producing useful products from microalgae: dependency on light which significantly complicates the process, increase costs, and reduced production of potentially useful products. As a general role, and in most cases, heterotrophic cultivation is far cheaper, simpler to construct facilities, and easier than autotrophic cultivation to maintain on a large scale. This capacity allows expansion of useful applications from diverse species that is now very limited as a result of elevated costs of autotrophy; consequently, exploitation of microalgae is restricted to small volume of high-value products. Heterotrophic cultivation may allow large volume applications such as wastewater treatment combined, or separated, with production of biofuels. In this review, we present a general perspective of the field, describing the specific cellular metabolisms involved and the best-known examples from the literature and analyze the prospect of potential products from heterotrophic cultures.

Single-cell proteins

Both photosynthetic and nonphotosynthetic microorganisms, grown on various carbon and energy sources, are used in fermentation processes for the production of single-cell proteins. Commercial-scale production has been limited to two algal processes, one bacterial process, and several yeast and fungal processes. High capital and operating costs and the need for extensive nutritional and toxicological assessments have limited the development and commercialization of new processes. Any increase in commercial-scale production appears to be limited to those regions of the world where low-cost carbon and energy sources are available and conventional animal feedstuff proteins, such as soybean meal or fish meal, are in short supply.

Modelling of the enzymatic kinetically controlled synthesis of cephalexin: influence of diffusion limitation

In this study the influence of diffusion limitation on enzymatic kinetically controlled cephalexin synthesis from phenylglycine amide and 7-aminodeacetoxycephalosporinic acid (7-ADCA) was investigated systematically. It was found that if diffusion limitation occurred, both the synthesis/hydrolysis ratio (S/H ratio) and the yield decreased, resulting in lower product and higher by-product concentrations. The effect of pH, enzyme loading, and temperature was investigated, their influence on the course of the reaction was evaluated, and eventually diffusion limitation was minimised. It was found that at pH >or=7 the effect of diffusion limitation was eminent; the difference in S/H ratio and yield between free and immobilised enzyme was considerable. At lower pH, the influence of diffusion limitation was minimal. At low temperature, high yields and S/H ratios were found for all enzymes tested because the hydrolysis reactions were suppressed and the synthesis reaction was hardly influenced by temperature. The enzyme loading influenced the S/H ratio and yield, as expected for diffusion-limited particles. For Assemblase 3750 (the number refers to the degree of enzyme loading), it was proven that both cephalexin synthesis and hydrolysis were diffusion limited. For Assemblase 7500, which carries double the enzyme load of Assemblase 3750, these reactions were also proven to be diffusion limited, together with the binding-step of the substrate phenylglycine amide to the enzyme. For an actual process, the effects of diffusion limitation should preferably be minimised. This can be achieved at low temperature, low pH, and high substrate concentrations. An optimum in S/H ratio and yield was found at pH 7.5 and low temperature, where a relatively low reaction pH can be combined with a relatively high solubility of 7-ADCA. When comparing the different enzymes at these conditions, the free enzyme gave slightly better results than both immobilised biocatalysts, but the effect of diffusion limitation was minimal.

Polyethyleneimine in immobilization of biocatalysts

A variety of polymers with amino pendant groups have been accepted as suitable enzyme carriers. A number of synthesis strategies and techniques are adopted to anchor enzymes. The polymers are activated through derivatization either prior to or during adsorption to facilitate the covalent binding of enzyme. Polyethyleneimine (PEI), with the highest concentration of amino groups, has found acceptance as a carrier in a number of industrial immobilized biosystems. The two forms of PEI known are the linear crystalline type and the more important amorphous branched structure with a distribution of primary, secondary, and tertiary amino groups in the ratio 1:2:1. The primary and secondary amino groups are conveniently modified to generate facile enzyme carriers. A number of patents have been filed on the use of PEI to bind a rich variety of enzymes and whole cells. This review is primarily a compilation of these reports and purports to highlight the potential of PEI.

Expression of Different Levels of Ethanologenic Enzymes from Zymomonas mobilis in Recombinant Strains of Escherichia coli

The expression of Zymomonas mobilis genes encoding pyruvate decarboxylase and alcohol dehydrogenase II in Escherichia coli converted this organism from the production of organic acids to the production of ethanol. Ethanol was produced during both anaerobic and aerobic growth. The extent to which these ethanologenic enzymes were expressed correlated with the extent of ethanol production. The replacement of organic acids with ethanol as a metabolic product during aerobic and anaerobic growth resulted in dramatic increases in final cell density, indicating that these acids (and the associated decline in pH) are more damaging than the production of ethanol. Of the plasmids examined, the best plasmid for growth and ethanol production expressed pyruvate decarboxylase and alcohol dehydrogenase II at levels of 6.5 and 2.5 IU/mg of total cell protein, respectively.

The nature of biotechnology

This review introduces the multidisciplinary subject of biotechnology and the exploitation of the 'biomolecule'. The author describes practical applications of micro-organisms and biologically derived molecules. Some of these processes have been known for many years but recent developments have led to very rapid expansion of understanding and knowledge of the subject. Areas of the technology discussed include monoclonal antibodies, gene manipulation, enzymes, cell cultures, biosensors and biological processing products.

The acetone-butanol-ethanol fermentation

Renewed interest in the acetone-butanol-ethanol (ABE) fermentation as a route for industrial production of butanol has been evident since the oil crisis of the 1970s. The present review includes an historical recap of the traditional industrial process and culturing practices useful in maintaining viable solvent-producing cultures, and then summarizes new and exciting research on the physiology and genetics of the microorganisms as well as process design. Most of these reports relate to improvements in solvent yield and the overall process, since traditional production is not efficient under present economic conditions. Conclusions are then made on future developments necessary for the establishment of an economically viable industrial process.

Genetic engineering of ethanol production in Escherichia coli

The genes encoding essential enzymes of the fermentative pathway for ethanol production in Zymomonas mobilis, an obligately ethanologenic bacterium, were inserted into Escherichia coli under the control of a common promoter. Alcohol dehydrogenase II and pyruvate decarboxylase from Z. mobilis were expressed at high levels in E. coli, resulting in increased cell growth and the production of ethanol as the principal fermentation product from glucose. These results demonstrate that it is possible to change the fermentation products of an organism, such as E. coli, by the addition of genes encoding appropriate enzymes which form an alternative system for the regeneration of NAD+.

Simple-kinetic descriptions of alcohol dehydrogenase after immobilization on tresyl-chloride-activated agarose

Yeast alcohol dehydrogenase was successfully immobilized on tresyl-chloride-activated agarose; the optimized conditions allowed an enzyme activity recovery of over 90%. Comparison of free and immobilized enzyme properties showed an unchanged intrinsic activation energy of the reaction and a shift of optimum activity to a higher pH medium after immobilization. Comparison of the kinetic parameters for both substrates of the reaction showed that the Michaelis-Menten model could not take into consideration all the constraints induced by the immobilization on the enzyme properties but that the Theorell-Chance model was more appropriate. These results are discussed taking into consideration the factors affecting the immobilized enzyme. Finally, we discuss the possibilities of cofactor regeneration with this immobilized alcohol dehydrogenase.

Biotechnology in Food Production and Processing

The food processing industry is the oldest and largest industry using biotechnological processes. Further development of food products and processes based on biotechnology depends upon the improvement of existing processes, such as fermentation, immobilized biocatalyst technology, and production of additives and processing aids, as well as the development of new opportunities for food biotechnology. Improvements are needed in the characterization, safety, and quality control of food materials, in processing methods, in waste conversion and utilization processes, and in currently used food microorganism and tissue culture systems. Also needed are fundamental studies of the structure-function relationship of food materials and of the cell physiology and biochemistry of raw materials.