生物技术导论教案 - 天津科技大学

生物技术导论教案 - 天津科技大学

生物技术导论教案

1

生物技术导论教案 - 天津科技大学

生物技术导论（Introduction to biotechnology）课程教案Topic:Chapter 1 Overview of biotechnology

Learning targets：

1.Understanding the basic concepts of biotechnology.

2.Knowing the public conceptions of biotechnology.

3.Understanding the use of biotechnology in commercial production.

Key issues: biotechnology, genetic engineering, product safety.

Difficult issues: applications of biotechnology.

Teaching outline and time distribution:

1.1 Introduction 1.2 Applications of biotechnology

1.2.1 Medicine 1.2.2 Agriculture and food 1.2.3 Other industries 1.3 Public perception of biotechnology

1.4 Product safety

1.5 The future of biotechnology Methodology:

1.Describe the principles with help of practical cases;

2.Show pictures and photos;

3.Ask questions and summarizing;

4.Multiple media and handwriting;

2

生物技术导论教案 - 天津科技大学

Chapter 1 Overview of biotechnology

1.1I ntroduction

Biotechnology is technology based on biology, especially when used in agriculture, food science, medicine, and environment. United Nations Convention on Biological Diversity defines biotechnology as: “Any technological application that uses biological systems, dead organisms, or derivatives thereof, to make or modify products or processes for specific use.” And The European Federation of Biotechnology (EFB) considers biotechnology as “the integration of natural sciences and organisms, cells, parts thereof, and molecular analogues for products and services.”

In simple words biotechnology is any technological application which is used to make a change in a cell or in biological system. Biotechnology draws on the pure biological sciences (genetics, microbiology, cell biology, molecular biology, biochemistry) and in many instances is also dependent on knowledge and methods from outside the sphere of biology (physics, chemistry, mathematics). Conversely, modern biological sciences (including even concepts such as molecular ecology) are intimately dependent on the methods developed through biotechnology.

Historically, biotechnology evolved as an agricultural skill rather than a science. Through early biotechnology, farmers were able to use microbes to produce foods and beverages, such as bread and beer, and to modify plants and animals through progressive selection for desired traits.

The new biotechnology revolution began in the 1970s and early 1980s when scientists learned to alter precisely the genetic constitution of living organisms by processes outside of traditional breeding practices. This ‘genetic engineering’ has had a profound impact on almost all areas of traditional biotechnology and further permitted breakthroughs in medicine and agriculture, in particular, that would be impossible by traditional breeding approaches.

Some of the most exciting advances will be in new pharmaceutical drugs and therapies to improve the treatment of many diseases, and in the production of healthier foods, selective pesticides and innovative environmental technologies.

Since the 1980s biotechnology has been recognized and accepted as a strategic technology by most industrialized nations. Revenue in the industry over the world is expected to be more than 130 billion US dollars in 2007, and to grow by 12.9% in 2008. The economic returns from investing in strategic technologies accrue not just to

3

生物技术导论教案 - 天津科技大学

the companies conducting research and development (R&D) but more importantly returns to society overall are estimated to be even higher.

The present industrial activities to be affected most will include human and animal food production, provision of chemical feed stocks to replace petrochemical sources, alternative energy sources, waste recycling, pollution control, agriculture, aquaculture and forestry.

1.2A pplications of biotechnology

1.2.1Medicine

Most traditional pharmaceutical drugs are relatively simple molecules that have been found primarily through trial and error to treat the symptoms of a disease or illness. Biopharmaceuticals are large biological molecules known as proteins and these usually target the underlying mechanisms and pathways of a disease. It is a relatively young industry. They can deal with targets in humans that may not be accessible with traditional medicines.

Biotechnology is commonly associated with landmark breakthroughs in new medical therapies to treat hepatitis B, hepatitis C, cancers, arthritis, haemophilia, bone fractures, multiple sclerosis, and cardiovascular disorders. The biotechnology industry has also been instrumental in developing molecular diagnostic devices that can be used to define the target patient population for a given biopharmaceutical.

Modern biotechnology can be used to manufacture existing medicines relatively easily and cheaply. The first genetically engineered products were medicines designed to treat human diseases. Modern biotechnology has evolved, making it possible to produce more easily and relatively cheaply human growth hormone, clotting factors for hemophiliacs, fertility drugs, erythropoietin and other drugs. Most drugs today are based on about 500 molecular targets. Genomic knowledge of the genes involved in diseases, disease pathways, and drug-response sites are expected to lead to the discovery of thousands more new targets.

1.2.2Agriculture and food

Agriculture and Food is more important economically than health-care, even in western countries, and is clearly of much greater concern to the rest of the world.

Biotechnology has been widely used in agriculture and food in many areas. For example, using the techniques of modern biotechnology, one or two genes may be transferred to a highly developed crop variety to impart a new character that would increase its yield. Moreover, crops containing genes that will enable them to

4

生物技术导论教案 - 天津科技大学

withstand environmental stresses may be developed.

Biotechnological methods for improving field crops, such as wheat, corn and soybeans, are also being sought, since seeds serve both as a source of nutrition for people and animals and as the material for producing the next plant generation. By increasing the quality and quantity of protein or varying the types in these crops, we can improve their nutritional value.

Modern biotechnology can also be used to slow down the process of spoilage so that fruit can ripen longer on the plant and then be transported to the consumer with a still reasonable shelf life. This alters the taste, texture and appearance of the fruit. More importantly, it could expand the market for farmers in developing countries due to the reduction in spoilage.

1.2.3Other industries

Many other industries could, in principle, benefit from biotechnology. The fabric and textiles industries are using biotechnology quite substantially, using enzymes to treat textiles and leather, for example. The paper pulp industry is taking up biotechnology rapidly as a cleaner alternative to chemical and mechanical processes. The plastics industry also uses some polymers made by micro-organisms.

Other biomaterials such as xanthan gums are used in some specialized industrial applications, but this is rare and opportunistic, and usually does not exploit our systematic knowledge of biological systems, but only our accidental knowledge of their properties and products. This is because oil is very cheap, and the industry for converting it into products is flexible, efficient and sophisticated.

1.3P ublic perception of biotechnology

While biotechnology presents enormous potential for healthcare and the production, processing and quality of foods through genetic engineering of crops, fertilizers, pesticides, vaccines and various animal species, the implications of these new biotechnological processes go well beyond the technical benefits offered.

Central to most of the debates about biotechnology is the single main issue – should regulation be dependent on the characteristics of the products modified by (rDNA) technology? The product versus process debate has continued for many years and exposes conflicting views on what should represent public policies on new technology development. What is public interest? Should this be left to the scientists and technologists to decide, or should the ‘public’ become part of such decision-making processes? The many crucial decisions to be made will affect the

5

生物技术导论教案 - 天津科技大学

future of humanity and the planet’s natural resources.

In fact, public debate is essential for new biotechnology to grow up, and undoubtedly for the foreseeable future biotechnology will be under scrutiny. Public understanding of these new technologies could well hasten public acceptance. However, the low level of scientific literacy (e.g. in the USA where only 7% are scientifically literate) does mean that most of the public will not be able to draw informed conclusions about important biotechnology issues. Consequently, it is conceivable that a small number of activists might argue the case against genetic engineering in such emotive and ill-reasoned ways that both the public and the politicians are misled. The biotechnology community needs to sit up and take notice of, and work with, the public. People influence decision-making by governments through the ballot box or through the presence of public opinion.

While genetic engineering is an immensely complicated subject, not easily explained, that doesn’t mean that it must remain, in decision-making terms, only in the control of the scientist, industrialist or politician. There is no doubt that many of the public or consumers are interested in the science of genetic engineering but are unable to understand the complexity of this subject. Furthermore, genetic engineering and its myriad of implications must not be beyond debate. Public attitudes to genetic engineering will influence its evolution and marketplace applications. It is important for public confidence for everyone to recognize that all science is fallible-especially complex biological science. All too often press and TV reports on genetic engineering present the discoveries as absolute certainties when this is rarely the case

1.4 Product safety

Much debate is now taking place on the safety and ethical aspects of genetically modified organisms (GMOs) and their products destined for public consumption. Can such products with ‘unnatural’ gene changes lead to unforeseen problems for present and future generations?

The safety of the human food supply is of critical importance to most nations and all foods should be fit for consumption i.e. not injurious to health or contaminated. When foods or food ingredients are derived from GMOs they must be seen to be as safe as, or safer than, their traditional counterparts. The concept of substantial equivalence is widely applied in the determination of safety by comparison with analogous conventional food products together with intended use and exposure.

When such novel products are moving into the marketplace the consumer must be assured of their quality and safety. Thus there must be toxicological and nutritional

6

生物技术导论教案 - 天津科技大学

guidance in the evolution of novel foods and ingredients to highlight any potential risks which can then be dealt with appropriately. Safety assessment of novel foods and food ingredients must satisfy the producer, the manufacture, the legislator and the consumer. The approach should be in line with accepted scientific considerations, the results of the safety assessment must be reproducible and acceptable to responsible health authorities and the outcome must satisfy and convince the consumer.

In biotechnology, governmental regulations will represent a critical determinant of the time and total costs in bringing a product to market. Regulatory agencies can act as ‘gate-keepers’ for the development and availability of new biotechnology products, but can also erect considerable barriers to industrial development.

1.5 The future of biotechnology

Biotechnology is increasingly being viewed as a Promethean science, because in so many ways it is transforming the relationship between humans and the planet. In recent years biotechnology has been shown to be a spectrum of enabling technologies, which are increasingly being applied in many aspects of modern society. A central feature of new biotechnological advances derives from an increasing understanding of the mechanisms of life and how these will eventually transform human lives, as well as giving a deeper appreciation of agriculture, aquaculture, forestry and the biological environment. The ability to select and manipulate genetic material within and outside species has permitted unprecedented opportunities to alter life forms for the benefit of society.

Many molecular biologists have postulated that a genetic or DNA sequence analysis of an inpidual could be predictive of future disease occurrence, e.g. cardiovascular, cancer, Alzheimer’s, etc. Undoubtedly, there will be continued research and application in this area. The further implementation of genomics and proteomics will allow a much deeper understanding of the biology of molecules, cells and whole organisms. Doctors and patients will have much to gain from the outcome of these studies. Much will be learned about human inpiduality and how these findings could influence inpidual health and disease susceptibility.

Plant-based genetic engineering started in the early 1980s with the development of the Ti plasmid of Agrobacterium, which has allowed the introduction of simple genetic constructs into most of the important crop plants. There is increasing evidence that GM crops are giving significant yield increases, savings for growers and pesticide use reductions in both developed and developing countries. Yet another important feature of certain GM plants is that they use less water, and undoubtedly in many

7

生物技术导论教案 - 天津科技大学

parts of the world water availability will be the determining factor for successful food production by both animals and plants.

The new aspects of biotechnology such as biofuel will bring huge benefits to humankind. Climate change is now a worldwide recognized concern. A number of approaches are now being considered to counter the effects of global warming. From a biotechnological consideration biofuel development has gained international recognition and a wide range of options are being progressed to determine which biofuels can become cost-effective alternatives to fossil fuels..

In summary, biotechnology will play a major role in the continued search for solutions to the many problems that will affect the society of tomorrow: health, food supply and a safe biological environment. And more scientific research will be continued to achieve these ends.

1.6 Further reading

Fumento M. (2003). Bioevolution: How Biotechnology is Changing our World. Encounter Books, USA.

John E. Smith (2009). Biotechnology (5th edition). Cambridge University Press, UK.

8

生物技术导论教案 - 天津科技大学

9

生物技术导论教案 - 天津科技大学

Chapter 2 Bioreactor

Bioreactors are the containment vehicles of any biotechnology-based production process, be it for brewing, organic or amino acids, antibiotics,enzymes, vaccines or for bioremediation. For each biotechnology process the most suitable containment system must be designed to give the cor-rect environment for optimising the growth and metabolic activity of the biocatalyst. Bioreactors range from simple stirred or non-stirred open con-tainers to complex aseptic integrated systems involving varying levels of advanced computer control (Fig.1).

Bioreactors occur in two distinct types (Fig.1. In the ?rst instance they are primarily non-aseptic systems where it is not absolutely essential to operate with entirely pure cultures, e.g. brewing, ef?uent disposal sys-tems; while in the second type, aseptic conditions are a prerequisite for successful product formation, e.g. antibiotics, vitamins, polysaccharides and recombinant proteins. This type of process involves considerable chal-lenges on the part of engineering construction and operation.The physical form of many of the most widely used bioreactors has not altered much over the past forty years; however, in recent years, novel forms of bioreactors have been developed to suit the needs of speci?c bioprocesses and such innovations are ?nding increasingly specialised roles in bioprocess technology (Fig.

1).

In all forms of fermentation the ultimate aim is to ensure that all parts of the system are subject to the same conditions. Within the bioreactor the microorganisms are suspended in the aqueous nutrient medium con-taining the necessary substrates for growth of the organism and required product formation. All nutrients, including oxygen, must be provided to diffuse into each cell and waste products such as heat, carbon dioxide and waste metabolites removed.

10

生物技术导论教案 - 天津科技大学

Fig. 1 Various forms of bioreactor.

(a) Continuous stirred tank reactor.

(b) Tower reactor.

(c) Loop (recycle) bioreactor.

(d) Anaerobic digester or bioreactor.

11

生物技术导论教案 - 天津科技大学

(e) Activated sludge bioreactor. (Source: (a) and (b)reproduced by permission from Kristiansen and Chamberlain, 1983.)

Table1 Standards of materials used in sophisticated fermenter design

The concentration of the nutrients in the vicinity of the organismmust be held within a de?nite range since low values will limit the rate of organ-ism metabolism while excessive concentrations can be toxic. Biological reactions run most ef?ciently within optimum ranges of environmental parameters, and in biotechnological processes these conditions must be provided on a micro-scale so that each cell is equally provided for. When the large scale of many bioreactor systems is considered it will be realized how dif?cult it is to achieve these conditions in a whole population. It is here that the skills of the process or biochemical engineer and the micro-biologist must come together.

Fermentation reactions are multiphase, involving a gas phase (containing N2,O2 and CO2), one or more liquid phases (aqueous medium and liquid substrate) and solid microphase (the microorganisms and possibly solid substrates). All phases must be kept in close contact to achieve rapid mass and heat transfer. In a perfectly mixed bioreactor all reactants entering the system must be immediately mixed and uniformly distributed to ensure homogeneity inside the reactor.

To achieve optimisation of the bioreactor system, the following operating guidelines must be closely adhered to:

(1) the bioreactor should be designed to exclude entrance of contaminating organisms as well as containing the desired organisms

(2) the culture volume should remain constant, i.e. no leakage or evaporation

(3) the dissolved oxygen level must be maintained above critical levels of aeration and culture agitation for aerobic organisms

(4) environmental parameters such as temperature, pH, etc., must be con-trolled and the culture volume must be well mixed.

The standard of materials used in the construction of sophisticated fermenters is

12

生物技术导论教案 - 天津科技大学

important (Table 1).

Fermentation technologists seek to achieve a maximisation of culture potential by accurate control of the bioreactor environment. But still there is a great lack of true understanding of just what environmental conditions will produce an optimal yield of organism or product. Organisms with large cell size, such as animal cells compared to bacteria, have a complex demand for nutrients and lower growth rate. On the other hand their ability to produce complicated proteins is increased.

Successful bioprocessing will only occur when all the speci?c growth-related parameters are brought together, and the information used to improve and optimise the process. For successful commercial operation of these bioprocesses quantitative description of the cellular processes is an essential prerequisite: the two most relevant aspects, yield and productivity, are quantitative measures that will indicate how the cells convert the substrate into the product. The yield represents the amount of product obtained from the substrate while the productivity speci?es the rate of product formation.

To understand and control a fermentation process it is necessary to know the state

of the process over a small time increment and, further, to know how the organism responds to a set of measurable environmental conditions. Process optimisation requires accurate and rapid feedback control. In the future, the computer will be an integral part of most bioreactor systems. However, there is a lack of good sensor probes that will allow on-line analysis to be made on the chemical components of the fermentation process.

A large worldwide market exists for the development of new rapid methods monitoring the many reactions within a bioreactor. In particular, the greatest need is

for innovatory microelectronic designs.

When endeavouring to improve existing process operations or design it is often advisable to set up mathematical models of the overall system. A model is a set of relationships between the variables in the system being studied. Such relationships are usually expressed in the form of mathe-matical equations but can also be speci?ed as cause/effect relationships,which can be used in the operation of the speci?c processes. The actual variables involved can be extensive but will include any parameter that is

of importance for the process and can include: pH, temperature, substrate concentration, agitation, feed rate, etc.

Bioreactor con?gurations have changed considerably over the last few decades. The original fermentation system was a shallow tank agitated or stirred by manpower.

13

生物技术导论教案 - 天津科技大学

From this has developed the basic aeration tower system, which now dominates industrial usage. As fermentation systems were further developed, two design solutions to the problems of aeration and agitation have been implemented. The ?rst approach uses mechanical aeration and agitation devices, with relatively high power requirements;the standard example is the centrally stirred tank reactor (CSTR), which is widely used throughout conventional laboratory and industrial fermentations. Such bioreactors ensure good gas/liquid mass transfer, have reason-able heat transfer, and ensure good mixing of the bioreactor contents.

The vertical shaft of the CSTR will carry one or more impellers depending on size of the bioreactor (Fig.1a). A broad range of impellers have been investigated for stirring and creating homogeneous conditions within the bioreactor. The impellers are usually spaced at intervals equivalent to one tank diameter along the shaft to avoid a swirling type of liquid movement. The six ?at-bladed (Rushton) turbine impellers are used in the majority of bioreactors and normally three to ?ve are mounted to achieve good mixing and dispersion throughout the system. The function of the impellers is to create agitation or mixing within the bioreactor and to facilitate aera-tion. The primary function of agitation is to suspend the cells and nutrient evenly throughout the medium, to ensure that the nutrients, including oxygen, are available to the cells and to allow heat transfer. Most industrial organisms are aerobic and, in most fermentations, the organisms will exhibit a high oxygen demand. Since oxygen is sparingly soluble in aqueous solutions (solubility of CO2 in water is about 30 times higher than that of O2) aerobic fermentations can only be supported by vigorous and constant aeration of the medium.

The second main approach to aerobic bioreactor design uses air distribution (with lowpower consumption) to create forced and controlled liquid ?ow in a recycle or loop bioreactor. In this way the contents are subjected to a controlled recycle ?ow, either within the bioreactor or involving an external recycle loop. Thus stirring has been replaced by pumping, which may be mechanical or pneumatic, as in the case of the airlift bioreactor.

The centrally stirred tank reactor consists of a cylindrical vessel with a motor-driven central shaft that supports one or several agitators with the shaft entering either through the top or the bottom of the vessels. The aspect ratio (i.e. height-to-diameter ratio) of the vessel is three to ?ve for microbial systems while for mammalian cell culture the aspect ratios do not normally exceed two. Sterile air is sparged into the bioreactor liquid below the bottom impeller by way of a perforated

14

生物技术导论教案 - 天津科技大学

ring sparger. The speed of the impellors will be related to the degree of fragility of the cells. Mammalian cells are extremely fragile when compared to most microorganisms. In a greatmany of the high-value processes the bioreactors will be operated in a batch manner under aseptic monoculture. The bioreactors can range fromc. 20L to in excess of 790m3 for particular processes. The initial culture expansion of the microorganisms will commence in the smallest bioreactor, and when growth is optimised it will then be transferred to a larger bioreactor, and so forth, until the ?nal operation bioreactor. Throughout such operations it is imperative tomaintain aseptic conditions to ensure the success of the process. Bioreactors are normally sterilised prior to inoculation and contaminationmust be avoided during all subsequent operations.If contamination occurs during the cultivation this will invariably lead to process failure since more often than not the contaminant can outgrow the participating monoculture.

The number of distinct types of bioreactor is quite limited when measured against the wide range of production processes and the varied biological systems involved. In industrial practice, and less as a result of special advantage than as a need for ?exibility in production equipment, the CSTR now occupies a dominant position and is virtually the only bioreactor design used in full-scale bioprocessing. Large amounts of organic waste waters from domestic and industrial sources are routinely treated in aerobic and anaerobic systems. Activated sludge processes are widely used for the oxidative treatment of sewage and other liquid wastes (Fig. 1d). Such processes use batch or continuous agitated bioreactor systems to increase the entrainment of air to optimize oxidative breakdown of the organic material. These bioreactors are large and for optimum functioning will have several or many agitator units to facilitate mixing and oxygen uptake. They are widely used in most municipal sewage treatment plants.

Anaerobic bioreactors or digestors have long been used to treat sewage matter. In the absence of free oxygen certain microbial consortia are able to convert biodegradable organicmaterial tomethane, carbon dioxide and new microbial biomass. Most common anaerobic digesters work on a continuous or semi-continuous manner.

An outstanding example of methane generation is the Chinese biogas programme where millions of family-size anaerobic bioreactors are in operation. Such bioreactors are used for treatment of manure, human excreta, etc., producing biogas for cooking and lighting and the sanitisation of the waste, which then becomes an excellent fertiliser. In almost all fermentation processes performed in a bioreactor there is generally a need to measure speci?c growth-related and environmental parameters, record them and then use the information to improve and optimise the process.

15

生物技术导论教案 - 天津科技大学

Bioreactor control measurements are made in either an on-line or an off-line manner. With an on-line measurement the sensor is placed directly within the process stream whereas for off-line measurement a sample is removed aseptically from the process stream and analysed. Bioreactor processing is still severely limited by a shortage of reliable instruments capable of on-line measurement of important variables such as DNA, RNA, enzymes and biomass. Off-line analysis is still essential for these compounds and since the results of these analyses are usually not available until several hours after sampling, they cannot be used for immediate control purposes. However, on-line measurement is readily available for temperature, pH, dissolved oxygen and carbon dioxide analyses.

The continued discovery of new products such as therapeutic drugs from microorganisms and mammalian cells will continue to depend on the development of innovative exploratory culture systems, which encourage the biosynthesis of novel compounds. New miniaturised, computer-controlled incubator systems with automated analysis units are now available as single units that can perform hundreds of experiments simultaneously, thus producing a wealth of data in a short time to facilitate optimum fermentation conditions for product formation. A new and quite novel approach involving combinatorial biology generates new products from genetically engineered microorganisms. DNA fragments or genes derived from unusual microorganisms that are not easily cultivated (recalcitrant microorganisms) can be transferred into easily cultivated or surrogate microorganisms and the resulting mixing and matching of genes encoding biosynthetic machinery is now offering the opportunity to discover new or modi?ed molecules or drugs. This could be of great signi?cance in antibiotic discovery.

While most high-value biotechnological compounds such as antibiotics and therapeutic proteins are produced in monoculture under strict conditions of asepsis there are now new avenues of research exploring product formation from mixed culture systems. Such systems may well produce different patterns of metabolites or indeed novel metabolites as a result of interactions that can occur between competing microorganisms. Because of the complexity of these mixed organism processes, they have all but been ignored by the scienti?c community. Monoculture under aseptic conditions is totally unnatural and rarely, if ever, occurs in nature. The norm is for microorganisms to exist together in the environment and to compete and respond to substrate availability and to the prevailing environmental conditions.

16

生物技术导论教案 - 天津科技大学

Topic: Chapter 3 Biotransformation

Learning targets：

1.Understanding what is biotransformation and the biotransformation process

2.Knowing the methods of biocatalyst selection

3.Understanding why should biocatalyst be immobilised

4.Knowing the methods of biocatalyst immobilisation

5.Understanding the main application of biotransformation

Key issues: Biocatalyst selection, methods of biocatalyst immobilisation, use of biotransformation in industry.

Difficult issues: “Metagenome” approach, metabolic pathway and protein engineering of existing biocatalysts, biotransformation application. Teaching outline and time distribution:

3.1 Introduction 10min 3.2 Biocatalyst selection

3.2.1 Screening for novel biocatalysts 10min 3.2.2 Use of existing biocatalysts 10min 32.3 Genetic modification of existing biocatalysts 10min 3.3 Biocatalyst immobilisation and performance

3.3.1 Biocatalyst immobilisation 15min 3.3.2 Methods of immobilisation 15min 3.4 Biotransformation application 20min Methodology:

1.Describe the principles with help of practical cases;

2.Show pictures and photos;

3.Ask questions and summarizing;

4.Multiple media and handwriting.

17

生物技术导论教案 - 天津科技大学

Chapter 3 Biotransformation

3.1 Introduction

Biotransformation is the process whereby a substance is converted into a product in a limited number of enzymatic steps by the use of biological catalysts. Biocatalysis can be broadly defined as the use of biological molecules to catalyse specific chemical reactions. The biological catalyst can be used as an enzyme, resting whole cells or a whole, dead microorganism (that contains an enzyme or several enzymes). The extensive examination of factors required for the establishment of an efficient biotransformation process affect the development of optimal biocatalysts, reaction media and bioreactors (Fig.1). Metabolic transformations or metabolism are terms frequently used for the biotransformation process.

The opportunities for industrial use of biological catalysts for biotransformations include not only the traditional hydrolytic (e.g. protein and starch hydrolysis), isomerisation (e.g. glucose conversion to fructose) reactions but, more recently, synthesis of chiral compounds, reversal of hydrolytic reactions, complex synthetic

18

生物技术导论教案 - 天津科技大学

reactions such as aromatic hydroxylations and enzymatic group protection chemistry and degradation of toxic and environmentally harmful compounds.

Biological catalysts have the advantages of the reactions at near neutral pH, ambient temperatures and atmospheric pressures; industrially useful chemistry often requires extremes of these conditions. More importantly biocatalysts are highly reaction specific, enantiomer-specific and regio-specific, which lead to single enantiomeric products with regulatory requisites for pharmaceutical, food and agricultural use.

Biotransformations have been performed by a variety of biological catalysts, in the form of whole cells, isolated enzymes, immobilised enzymes or cells, to catalyze chemical reactions. Such biotransformations systems may be used for environmentally benign biocatalysis of synthetic reactions, bioremediation of pollutants, or waste beneficiation, a combination of these in which the biological catalysts convert industrial residues to useful chemical products. In each case, suitable biocatalysts with particular characteristics are required. The suitable biocatalysts must be selective, active and stable under operational conditions in terms of composition, concentration, pH, pressure and temperature. More rational screening and selection techniques are required to produce suitable biocatalysts. One is the isolation of biocatalysts, e.g. enzymes and cells, able to catalyse novel reactions of industrial interest. The other is the selection and designment of biocatalysts suitable for industrial use with improved operational stabilities and kinetic properties. A much greater understanding is required. This includes the machanisms of protein denaturation and decay of biocatalytic activities under process conditions and an evaluation of methods to maintain and improve biocatalyst stability, e.g. chemical modification, immobilisation and protein engineering.

The biotransformations have two purpose: one is to remove them from effluents and convert them to less toxic products, the other is to convert them into products with economic value. These reactions can be accomplished utilizing various isolated-enzyme, whole-cell, immobilised enzymes or cells biological catalysts.

3.2 Biocatalyst selection

19

本文来源：https://www.bwwdw.com/article/jl3n.html