9
Chapter 9 Genetic Manipulation
Genes have been manipulated by man for a very long time, that is if selective
breeding, which has been practised for centuries in agriculture and elsewhere
to develop desirable characteristics in domesticated animals and plants, is to be
considered as manipulation, as it rightly should. Even from the early days of
Gregor Mendel, the Moravian monk and pioneer of genetic analysis, plants were
bred to bring out interesting, useful and sometimes unusual traits. Many of these
are now lost to classical plant breeders because of divergence of strains leading
to infertile hybrids. One of the joys of genetic engineering is that in some cases,
ancient genes may be rescued from seed found in archaeological digs for example,
and reintroduced by transfer into modern strains. It has been proposed that the
exchange of genetic information between organisms in nature is considerably
more commonplace than is generally imagined (Reanney 1976) and could explain
the observed rates of evolution. In bacteria, the most likely candidates for genetic
transfer are plasmids and bacteriophage, and since eukaryotes lack plasmids,
their most plausible vectors are eukaryotic viruses. This, of course, is in addition
to DNA transfer during sexual reproduction. Current knowledge would suggest
that exchange involving a vector requires compatibility between the organism
donating the genetic material, the vector involved, and the recipient organism.
For example, two bacteria must be able to mate for plasmid transfer to take
place, or if a virus is involved as a vector, it must be able to infect both the
donor and recipient cells or organisms. However, there is evidence to suggest that
this view is somewhat na ̈ıve and that there is considerably more opportunity for
genetic exchange between all cells, prokaryotic and eukaryotic, than is popularly
recognised. This idea, proposed by Reanney (1976) is developed in Chapter 3.
Bacteria are notorious for their ability to transfer genes between each other as
the need arises thanks to the location on plasmids of most of the gene groups, or
operons, involved in the breakdown of organic molecules. Strong evidence for
the enormous extent of these ‘genomic pools’ comes from analysis of marine
sediment (Cooket al. 2001). Throughout this book, the point has been made that
micro-organisms involved in remediation do so in their ‘natural’ state largely
because they are indigenous at the site of the contamination and have developed
suitable capabilities without any external interference. However, sometimes after
a sudden contamination such as a spill, microbes are not able to amass useful
mutations to their DNA quickly enough to evolve suitable pathways to improve