Fundamentals of Biological Intervention 61of the genome and therefore operating under different parameters affecting gene
regulation. Transfer of genes across wide taxonomic gaps is made possible by
the mobile nature of ECEs many of which may cross species barriers often
resulting in the insertion of all or part of the ECE into the recipient genome.
Examples of such mobility are viruses which infect a wide host range, such as
some retroviruses, the alfalfa mosaic virus, and the Ti plasmid ofAgrobacterium
tumefacienswhich the bacterium introduces into plant cells. The retroviruses,
of which Human Immunodeficiency Virus (HIV) is an example, are unusual in
having RNA as their genetic material. They replicate in a manner which includes
double-stranded DNA as an intermediate and so may integrate into the host cell
genome. RNA viruses tend to be more susceptible than DNA viruses to mutation
presumably due to the less chemically stable nature of the macromolecule. They
have been invoked by Reanney (1976) as being the likely agents for the spread
of genetic information between unrelated eukaryotes. His observations led him to
conclude that there is only a blurred distinction between cellular and ECE DNA
both in eukaryotes and prokaryotes and further suggest that no organism lives in
true genetic isolation as long as it is susceptible to at least one of the classes of
ECEs described above. Clearly, for the mutation to be stabilised, it must occur in
inheritable DNA sequences, a situation reasonably easy to achieve in microbes
and at least possible in multicellular organisms.
The existence of genetic mobility has been accepted for many years, even
though the extent and the mechanisms by which it operates are still being elu-
cidated. From this knowledge several lessons may be learned; among them, that
the genetic environment of any organism may well be significant and that there
is some justification in viewing the principle of genetic engineering as perform-
ing in the laboratory, a process which is occurring in abundance throughout the
living world. This topic is explored further in Chapters 9, 10 and 11.
Closing Remarks
As has been seen, even within the brief discussion in this chapter, life on Earth
is a richly varied resource and the functional reality of biodiversity is that many
more metabolic pathways exist, particularly within the microbial melting pot,
than might be commonly supposed. As a result, a number of generally unfamil-
iar groups of chemicals and organisms have implications for the application of
environmental biotechnology which exceed their most obvious contributions to a
wider consideration of the life sciences. Hence, xenobiotics, as an example of the
former, represent a current problem for which the solution remains unresolved
and extremophiles, as the latter, hold the potential to revolutionise many indus-
trial procedures, thereby heralding major benefits in terms of ‘clean technology’.
There are many aspects of current environmental management for which there is
no presently relevant biotechnological intervention. However, this is not a static
science, either in terms of what can be done, or the tools available. Discoveries