Environmental Biotechnology - Chapter 11 potx

For one thing, many of these organisms are found in very specific and specialised ecological niches and replicating their optimum environmental requirements is likely to prove difficult, p

11 The Way Ahead

Implicit in the very essence of biotechnology is the idea of the use of biological systems for commercial benefit and consequently, as has been a recurrent theme throughout much of this book, this inescapably means that it is subject to business pressures Economic, legislative and political forces will shape the future of environmental biotechnology every bit as much as they have its past Such is the inherent nature of the subject At the same time, the use of biological solutions

in environmental applications depends on the current state of the art and this is ever changing as new developments are made One of the areas where major advancement may occur is in the field of biosensors

Biosensors

Some are currently available which have been very successful in environmen-tal monitoring of pollution A genetically modified yeast has been developed which detects oestrogen, 17ß-oestradiol and other molecules many of which are also endocrine disrupters Although this sensor was designed for use in human therapeutics, there is the potential for use in pollutant detection, especially in the light of concern over these chemicals in the watercourses, although consid-erable development is required (Tucker and Fields 2001) However, the use of biosensors for ‘one-off’ analyses such as in testing materials about to be tipped into landfill sites, must await refinement to a much higher level of reliability The possibility of producing them with enormous sensitivity and selectivity is becoming a reality with the development of ‘microchip’ type sensors combining

biological activity with nanowire electronics (Cui et al 2001a) This

technol-ogy has reached a stage of being able to detect a change in an electric current

attributable to the binding of a single molecule (Cui et al 2001b) Although these

studies raise exciting prospects for biosensors, the ‘ever-present’ question of cost remains for environmental applications

Manufacturing

In the manufacturing sphere, it seems certain that there will be increasing pres-sures to continue the reductions in pollution and waste production These are

related issues, of course, and both may be addressed by one of two general

approaches: a priori methods to avoid the problem in the first place or a posteriori

to clean it up more efficiently after the event Clean production methods, which have been variously discussed in Chapters 4 and 10, seem likely to play a grow-ing part in achievgrow-ing the former The use of various production biotechnologies will limit the environmental impact of ever more industrial processes by reducing their energy demands, the strength of effluents generated, the amount of waste requiring ultimate disposal and so on The growing importance of biocatalysis, and the general use of biological macromolecules in manufacturing procedures will, inevitably, lead to the development of novel and innovative techniques for many substances currently generated by conventional means There are many candidates for the forthcoming major roles in the bioindustrial production cycles

of the near future but probably amongst the most revolutionary and beneficial are likely to be found amid the ranks of the extremophiles, which were previously discussed in Chapter 3 Extremozymes isolated from these bacteria and archaea, which dwell happily in some of the most unlikely and biologically challenging

of environments on the planet, offer the potential to catalyse reactions previously the exclusive realm of physical chemistry Their potential lies both in primary action and secondary effect The first of these utilises enzymes obtained to bring about the desired effect, where such specificity of action is a natural characteris-tic of the donor microbe Secondary effects arise by virtue of the elucidation of the functionally key features of naturally occurring substances This allows the same mechanisms to be incorporated into artificial chemicals which subsequently achieve a goal for which no direct analogue exists in nature In this respect, for instance, further study of extremozymes isolated from hyperthermophilic organ-isms may well permit the mechanism of their heat tolerance to be discerned and the appropriate means incorporated into other, non-natural catalysts

The value of the extremozyme contribution has already been noted in the now well-established PCR technique, which enabled a major jump ahead to be made

in the whole science of biotechnology itself In addition, the commercial use

of an enzyme obtained from another thermophile to increase the efficiency of cyclodextrin production from cornstarch is a currently known example of clean technology Though these compounds are valued in the pharmaceutical and food industries, where they principally aid the stabilization of volatile ingredients, the process can still fairly be said to have an environmental component Improved manufacturing efficiencies typically go hand in hand with reduced pollution, waste production or energy demand In the future, this aspect of industrial activity seems set to assume far greater importance and extremophile research may well provide many of the necessary tools to make it possible

Thus, hyperthermophilic extremozymes have potential applications in many industries, offering amylases for confectionary or alcohol production, proteases for amino acid production, baking, brewing and detergents, xylanases for paper

bleaching, and dehydrogenases and oxidoreductases for a variety of commer-cial uses

In the chemical industry, the possible use of whole-organism hyperthermophiles offers new ways to produce hydrogen, methane and hydrogen sulphide At tem-peratures between 18–80◦C and under anaerobic conditions, this latter gas, for

example can be made by Desulfuromonas from elemental sulphur The

conven-tional chemical catalysis system requires a temperature of 500◦C or more to yield the same result Unsurprisingly then, the potential of whole-cell microbial biocatalytic methods and their notably superior specificity, is viewed with great interest In future, it may be possible to redesign the configuration of conven-tional bioreactors to produce efficient, high temperature substitutes for many of the currently standard industrial processes

Other extremophiles could also have roles to play Psychrophiles may yield enzymes which will function at the low refrigerator temperatures typically required to avoid spoilage in food processing, for enhanced cold-wash ‘biological’ washing powders and in perfume manufacture, reducing evaporative fragrance losses A use has been suggested for halophile enzymes in increasing the amount of crude oil extracted from wells, though whether this will ever be

a commercial reality remains to be seen and, moreover, leaves aside any consideration of the ‘environmental’ aspects of increased fossil fuel extraction Acidophilic extremozymes may one day form catalysts in chemical syntheses in acid solution, and alkaliphile derived proteases and lipases may replace existing versions in washing detergents to enhance their action In addition, some of the textile industry’s enzyme-using processes may see alkaliphilic extremozymes replacements for greater efficiency

However exciting the prospects of extremophile use may be, turning their potential into industrially deliverable processes will not be straightforward For one thing, many of these organisms are found in very specific and specialised ecological niches and replicating their optimum environmental requirements is likely to prove difficult, particularly within bioreactor systems initially designed around mesophile cultivation Hence, new types of reactors and, possibly, novel solid-state fermentation techniques may need to be developed before this can

be achieved Commercial-scale cultures of extremophiles for extremozyme har-vesting is also likely to prove problematic, since by virtue of their habitats, it is rare to find large numbers of any given single species in nature For such pur-poses, the isolation and purification of the required microbial culture to be grown

up is generally both difficult and costly to do Though the extremozymes can

be produced using recombinant DNA methods, as were discussed in Chapter 9, avoiding the need for wholesale, mass culturing of the extremophiles themselves, any industrial attempt at whole organism biocatalysis will, of course, demand it Despite the clear biotechnological potential of extremophile clean manufac-turing, a complete comparison between these emergent technologies and con-ventional methods will inevitably be required before they are likely to gain

mainstream industrial acceptance There is no doubt that they have advantages, but issues like cost and guaranteed reliability will prove vital in their uptake Clean manufacturing as a field appears to have a major contribution to make

to the environmental cause and there are a number of possible novel manufactur-ing biotechnologies emergmanufactur-ing Particularly when implemented alongside ‘green’ chemical processes, they promise significant advances in pollution reduction over the coming years

Waste Management

The second of the intervention points, waste management, is also likely to see major changes in the future, which are almost certain to be driven by external pressures to restrict the entry of biologically active material into the disposal loop With strict diversionary and recycling targets increasingly becoming the accepted norm in many countries of the world, it seems certain that biowaste will

be subject to expressly biological treatment at a previously unprecedented rate

It appears reasonable to assume that this will lead to an upsurge in the amount of waste destined for existing biooptions like anaerobic digestion and composting rather than any burgeoning evolution of new treatment technologies, particularly

in the case of domestic waste In addition, if clean manufacturing techniques based on biological systems become established, the amount of biodegradable waste produced in the first place should fall, though this does not allow for the contribution of normal refuse production growth, which seems to average around 5% increase per year

The role of integrated technologies in dealing with waste while simultaneously allowing components, either material or energy, to re-enter the chain of commer-cial utility is likely to prove a vital one In whatever form this most fundamental

of recycling is achieved, an adequate final market is essential Whether the end product is fundamentally reclaimed humus and minerals or a useable fuel, with-out a genuine and environmentally beneficial end-use of some kind, the whole operation becomes little more than an exercise in shifting the problem from one place, to another This is a criticism which has been levelled at environmental biotechnology at various times over the years and, on occasions, with some jus-tification A rational use for biomass energy is unlikely to be hard to find; a mass market for vast amounts of compost, particularly if of questionable quality, may not be so easy How the ideals of carbon sequestration are best translated into reality is still an area of some debate and will probably remain so well into the foreseeable future

One of the great advantages of waste biotechnologies, especially when applied

to domestic refuse, is the ease with which they can be incorporated into treatment trains Indeed, biological waste treatment naturally lends itself to many applica-tions which enable very effective maximisation of overall process efficiency to

be achieved, which is an important aspect to be considered in the planning of

any intervention or structured response Local authorities and, increasingly, com-mercial operations, are commonly faced with the need to make hard decisions regarding their waste management provision The inherent flexibility and intrinsic pollution mitigation offered by engineered biotreatment, as opposed to disposal and consequent incidental biodegradation, remains a major influential factor in this respect

Pollution Control

The future of pollution control and minimisation is, clearly, highly interdependent

on the forthcoming activities within the preceding two intervention zones With cleaner production techniques in the offing and more comprehensive biological treatment of the waste produced, not to mention the economic, legal and

pub-lic relations constraints operative, de novo contamination should be very largely

reduced The clean-up of historically polluted sites seems likely to become a growth area for a number of reasons The economic balance between bioremedi-ation and other forms of removal or disposal appears to be shifting on a global perspective In addition, the spiralling demand for commercial and housing land

in many parts of the world seems set to create compelling incentives for the reclamation and redevelopment of old sites

In this respect phytoremediation is a technology likely to see much greater development in the future, since its initial uses have been largely successful, though generally limited in scale There are clearly many advantages to the use

of whole organisms which can be managed using existing husbandry methods and the presence of which on a site is almost universally welcomed However, not all of the approaches available to biotechnology are so well received

Genetically Manipulated Organisms

There is a great deal of alarm felt by the general public with regard to the safety of genetically manipulated organisms (GMOs) being released into the environment, especially as the knowledge is not available to state categorically exactly the risk involved in the horizontal spread of the ‘foreign’ genes There is much active research addressing the spread of introduced genes, for example, in the use of chloroplasts as targets for ‘foreign’ DNA rather than the plant genome This, and various other issues raised by the use of recombinant DNA technology in envi-ronmental biotechnology, are addressed in a recent review (Daniell 1999) These may be approached at many levels with regard to environmental biotechnology,

as opposed to biotechnology in general

An obvious area for the future involvement of GMOs, or their products, would

be in the development of biosensors like the example given earlier Their use is

likely to be confined to the laboratory or ‘field’ test kits, and so are unlikely to warrant concern with regard to creating their own environmental pollution

It has already been noted that GMOs are unlikely to occupy a significant niche

in bioremediation, principally due to the high cost in developing such organisms set against the low financial return on remediation Where they are likely to be of great benefit is in solving problems for which no cheaper or simpler alternative technology is available; examples of these are not widespread

However, genetic engineering does, and will continue to, find a role in clean technology as in examples quoted in Chapter 10 There is great potential to develop ‘designer biocatalysts’, either as isolated enzymes, or as whole cells, which should go a long way to helping industry improve its profitability and environmental profile (Burton, Cowan and Woodley 2002) The picture is also somewhat different where environmental biotechnology strays into agribiotech-nology Here the potential for the development of genetically modified plants with improved quality or increased resistance to harsh conditions or pathogens,

as described in Chapters 9 and 10, is apparent

Concerns about the safety of such constructs should be viewed in the light

of discussions in Chapter 3 emphasising the natural mobility of genetic mate-rial In nature, there is a considerable amount of genetic exchange even between unrelated organisms A powerful example is that of the insertion of the Ti

plas-mid of the bacterium, Agrobacterium tumefaciens, into plant cells and another is

the ‘mariner’ gene shown to have ‘jumped ‘ from tsetse fly to human (Edwards 2000) A criticism frequently levied at genetic engineering is that it crosses species boundaries, thereby transferring genes into organisms which could never

be recipients An appreciation of the potential degree of genetic rearrangement and exchange through the activities of plasmids, viruses and transposable ele-ments leads to the conclusion that genetic engineering can be viewed as a very tiny part of the overall picture Furthermore, considering that there is an argument suggesting a blurring between genomic and extrachromosomal genes, it seems unrealistic to describe any gene as truly ‘foreign’ when the genome is proba-bly carrying an array of genetic material originating from a variety of sources Generally, public alarm comes with the widespread release of large numbers of specially engineered organisms into the environment, carrying genes which may

be envisaged causing an environmental problem greater than the one they seek to solve Such examples would be GM plants carrying genes for increased herbicide

or pesticide resistance

In Chapters 9 and 10, reference was made to baculoviruses being used as insecticides There are many reasons why this appears to be a relatively safe agent given that these nuclear polyhedrosis viruses (NPVs) are unable to infect plants, microorganisms, vertebrates, or nonarthropod invertebrates Assuming that this argument is not invalidated by alteration to the host range, recombinant baculoviruses should be even safer, since normally the protective polyhedrin protein gene has been sacrificed in favour of the ‘foreign’ gene This lack of

polyhedrin protein would be expected to lessen NPV survival in the wild and certainly reduce their infectivity thus making them poor vectors for the spread

of ‘foreign’ genes

Another area of major concern is that that many of the constructs released into the environment carry genes for antibiotic resistance In Chapter 9, the rationale for including such genes was described but, briefly, its function is during the con-struction of the recombinant and, especially in eukaryotic recombinants, serves

no function in the final GMO This being the case, it can be argued that it is reasonable to require the removal of all such selector and reporter genes before release of the GMO Accordingly, it is especially true because of the limited number of selector and reporter genes in current use Consequently, it is likely that while the gene or genes of interest may be unique, or almost so, to that construct, it will probably be carrying one of a very limited number of selector

or reporter genes As a result, the total number of GMOs released worldwide in one year, carrying one particular selector or reporter gene could be very high indeed Given that true figures for the rate of gene transfer between unrelated organisms (horizontal transfer) have not yet been satisfactorily estimated, it would seem prudent to err on the side of caution and remove all unnecessary genetic material, prior to GMO release

Attempts to estimate the rate of gene transfer in the environment are being made using microcosms These are small-scale reproductions of an enclosed test environment One such experiment investigated the effect of simulated light-ning on the rate of plasmid transfer between bacteria Their results showed an increase in transformation suggesting that, under certain conditions, lightning is able to make bacterial cells competent to receive plasmid DNA by horizontal transfer (Demaneche 2001) Microcosms are useful test systems especially as

in this example, where the question being asked is very specific, but they have their limitations in the assessment of wider horizontal gene transfer, due to the difficulties in recreating the natural environment It seems likely that many ques-tions regarding the spread of genes will not be answered until sufficient GMOs have been released and the ensuing results monitored It is clear that much more research is required into the balance between real benefits and risks of genetically engineered plants (Wolfenbarger and Phifer 2000)

Closing Remarks

In the final analysis, life is enormously robust and resilient, not perhaps at an individual level, but certainly on a gross scale Living things, and most especially microbes, have colonised a truly extensive range of habitats across the planet, and some of these are, as has been discussed, extremely challenging places This, combined with the lengthy history of bacteria and archaea, which has equipped many species with an amazing array of residual metabolic tools, adds up to a remarkable reservoir of capabilities which may be of use to the environmental

biotechnologist Humanity recently celebrated the turning of the millennium – the passage of 40 generations of our species On this basis, a bacterial ‘millennium’ passes in less than a day There is a tendency, particularly in older biology textbooks, to describe bacteria and their kin as ‘primitive life forms’ While, of course, this is true in terms of relative organisational complexity, it can encour-age a sort of unwarranted phylum-ist view of our own evolutionary superiority With 40 generations passing in under 24 hours and predating our own earliest beginnings by several hundreds of millions of years, prokaryotes are clearly far more highly evolved than ourselves or any other form of life on earth Unsurpris-ingly, then, many of the environmental problems encountered today have readily available solutions which make use of the natural cycles, pathways and abilities

of entirely unaltered micro-organisms

As this book has been at pains to point out, while there may well be a role for the use of GMOs in some applications, it seems unlikely that engineered organisms will assume centre-stage in the field Part of the reason is that there may simply be no need; there are enough odd abilities around quite naturally Scientists from the US Geological Survey recently announced the discovery of hydrogenotrophic archaean methanogens living 200 metres below the surface of

Lidy Hot Springs, Idaho (Chapelle et al 2002) This microbial community is

unlike any previously discovered; normally arachea seldom comprise more than 1–2%, but here, in conditions of low organic carbon content (around 0.27 mg/l) but significant levels of molecular hydrogen, they amount to around 99% of the population Under normal circumstances these archaeans, being less efficient energetically, are out-competed by ‘normal’ carbon-eating microbes, but in the absence of solar energy, which drives ecosystems based on utilising organic carbon, conditions heavily favour them

This has been seen as particularly relevant to the search for extraterrestrial life, since finding living systems on earth in environments analogous to those believed to exist on Mars or the Jovan moon, Europa, could provide vital clues

In many ways, perhaps it has even more relevance as a testimony to the extraor-dinary biodiversity of this planet and to the enormous potential of its collective gene pool

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