Fundamentals of Biological Intervention - Environmental Biotechnology: Theory and Application - page 54

soil under wood chips or the forest floor in North East USA. In addition to
their cellulolytic activity, these Clostridia were also found to be mesophilic,
nitrogen fixing, spore forming and obligate anaerobes. (Monserrate, Leschine
and Canale-Parola, 2001) Again, there is interest in this organism with regard to
clean technology in the hope that it may be used to convert cellulose into indus-
trially useful substances. A note of caution is that cellulose is a major product
of photosynthesis and, being the most abundant biopolymer on this planet, has a
vital role to play in the carbon cycle. Large scale disturbance of this balance may
have consequences to the environment even less welcome than the technologies
they seek to replace. However, judicious use of this biotechnology could reap
rewards at many levels.
Bacteria have also adapted to degrade man-made organics called xenobiotics.
Xenobiotics and Other Problematic Chemicals
The word is derived from the Greek 'x enos ' meaning foreign. Throughout this
topic the definition used is that xenobiotics are compounds which are not pro-
duced by a biological procedure and for which no equivalent exists in nature.
They present a particular hazard if they are subject to bioaccumulation especially
so if they are fat soluble since that enables them to be stored in the body fat of
organisms providing an obvious route into the food chain. Despite the fact that
these chemicals are man made, they may still be degraded by micro-organisms
if they fit into one of the following regimes; gratuitous degradation, a process
whereby the xenobiot resembles a natural compound sufficiently closely that it
is recognised by the organism's enzymes and may be used as a food source, or
cometabolism where the xenobiot is degraded again by virtue of being recog-
nised by the organism's enzymes but in this case its catabolism does not provide
energy and so can not be the sole carbon source. Consequently, cometabolism
may be sustained only if a carbon source is supplied to the organism. The ability
of a single compound to be degraded can be affected by the presence of other
contaminants. For example, heavy metals can affect the ability of organisms to
grow, the most susceptible being Gram positive bacteria, then Gram negative.
Fungi are the most resistant and actinomycetes are somewhere in the middle. This
being the case, model studies predicting the rate of contaminant degradation may
be skewed in the field where the composition of the contamination may invalidate
the study in that application. Soil microorganisms, in particular are very versatile
and may quickly adapt to a new food source by virtue of the transmission of
catabolic plasmids. Of all soil bacteria, Pseudomonads seem to have the most
highly developed ability to adapt quickly to new carbon sources. In bacteria, the
genes coding for degradative enzymes are often arranged in clusters, or operons,
which usually are carried on a plasmid. This leads to very fast transfer from
one bacterium to another especially in the case of Pseudomonas where many of
the plasmids are self-transmissible. The speed of adaptation is due in part to the
exchange of plasmids but in the case of the archaeans particularly, the pathways