Genetic Manipulation - Environmental Biotechnology: Theory and Application - page 212

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
their fitness for that changed environment, and so they may be 'trained' by the
artificially accelerated expansion of pre-existing pathways. The final option is
that they may be genetically engineered. Organisms which represent the 'norm',
frequently being the most abundant members occurring in nature, are described
as 'wild type'. Those with DNA which differs from this are described as mutant.
Alteration can be by the normal processes of evolution which constantly pro-
duce mutants, a process which may be accelerated artificially, or by deliberate
reconstruction of the genome, often by the introduction of a gene novel to that
organism. This latter route is the basis of GE which has several advantages over
traditional breeding or selection techniques. The process is specific, in that one
gene, or a selected group of genes, is transferred and so the mutation is quite
precise. There is flexibility in the system in that, depending on the modifications
made to the genome, a new product may be produced or the level of expression
of the existing product or products may be altered in quantity or proportions to
each other. This whole subject of proteomics is a discipline in its own right on
which volumes are published. Another advantage often quoted is that GE allows
genes to be transferred between totally unrelated organisms. The preceding dis-
cussion suggests that this is not a phenomenon unique to GE, but it is at least
defined and specific.
Training: The Manipulation of Bacteria Without
Genetic Engineering
A general procedure is to take a sample of bacteria from, at, or near, the site of
contamination from which a pure culture is obtained in the laboratory and iden-
tified, using standard microbiology techniques. The 'training' may be required
either to improve the bacterium's tolerance to the pollutant or to increase the
capabilities of pathways already existing in the bacterium to include the ability
to degrade the pollutant, or a combination of both. Tolerance may be increased
by culturing in growth medium containing increasing concentrations of the pol-
lutant so that, over successive generations, the microbe becomes more able to
withstand the toxic effects of the contaminant. Reintroduction of these bacteria
to the polluted site should give them an advantage over the indigenous bacte-
ria as they would be better suited to survive and remediate the contamination.
Improving the microbes ability to degrade a contaminant, sometimes referred
to as catabolic expansion, may be increased by culturing the bacteria in growth
medium in which the contaminant supplies an essential part of the nutrition, such
as being the only carbon source. Only bacteria which have undergone a muta-
tion enabling them to utilise this food source will be able to survive and so the
method effectively selects for the desired microbe; everything else having died.
It has been argued that under laboratory conditions where cultures of bacteria
are isolated from each other to prevent cross-contamination, mutations are most