Genetic Manipulation - Environmental Biotechnology: Theory and Application - page 211

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 lead-
ing to infertile hybrids. One of the joys of genetic engineering (GE) 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;
Hehemann et al ., 2010) and could explain the observed rates of evolution. In
bacteria, the most likely candidates for genetic transfer are plasmids and bac-
teriophage, and since eukaryotes lack plasmids, their most plausible vectors are
eukaryotic viruses. This, of course, is in addition to DNA transfer during sexual
reproduction. Existing knowledge would suggest that exchange involving a vec-
tor 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 naive 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 breakdown of organic molecules. Strong evidence for
the enormous extent of these 'genomic pools' comes from analysis of marine
sediment (Cook et al ., 2001). Throughout this topic, the point has been made
that microorganisms 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