Integrated Environmental Biotechnology 253largely beyond the scope of this book to discuss. Suffice it to say that, in any
novel application, cost is a major issue and although the potential market may be
enormous, the commercial benefits must be clear. As discussed before, the attitude
of industry will be crucial. There is undoubtedly a strong background interest in
bioproducts, but machinery is often extremely expensive, and down-time is costly
and inconvenient. Using a bioengineered substitute which has not been tested and
approved, often represents a huge commercial gamble, and it is a risk which few
enterprises, understandably, can afford to take. It may be some time before the
oft-quoted image of vast areas of transgenic crop plants growing the biological
equivalents of today’s petroleum-based products, at no more cost than cabbages
or corn, finally becomes a commercial reality. However, the beginnings are clear.
The search for a biological method of producing plastics, for example, already
shows some promise. The ability of some bacteria to produce natural polymers
has been known for some time and a number of attempts at growing plastics
have been made. The products typically proved expensive, costing between
three and five times as much as ordinary plastic and were generally found to
be too brittle for normal use. Poly(hydroxyalkanoates) are a class of natural
polymers with thermoplastic properties, which can be synthesised by bacteria,
though the process is itself economically uncompetitive. Using green plants
as plastics factories promises much greater competitiveness, but guaranteeing
the appropriate monomer composition is not easy. One solution was recently
demonstrated using genetically modified varieties of oilseed rape and cress,
engineered to produce poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) a
Poly(hydroxyalkanoate) with commercial applicability, within their leaves and
seeds (Slateret al. 1999). In effect, this is a perfect example of genetic engineer-
ing manipulating the respective strengths of contributory organisms to optimise
their functional isolated potential. Inserting the bacterial genes responsible for
plastic production intoArabidopsis andBrassica plants, avoids the expense
of feed, since photosynthesis naturally provides the necessary carbon and the
metabolic flow of intermediates from fatty acid and amino acid synthesis is redi-
rected for plastic production. The PHBV biosynthesised in plant plastids appears
to be of a marketable type and quality, though the yield was relatively low. The
process will need some refining if it is to be a realistic proposition for serious
commercial production.
Clearly, if and when it is, returning to the intervention triangle model to
consider the agricultural benefits of specificallyenvironmentalbiotechnology,
it will represent a major advance in both ‘clean’ production and pollution con-
trol. While the former may largely remain for the future, in many ways the latter
is already achievable.
Microbial pesticides
Chemical pesticides are problematic for many reasons. Firstly, although
some degradation occurs as described in Chapter 4, pesticides are notoriously