56 Environmental Biotechnology
a large extent requiring little modification if any to utilise new xenobiotics. Even
so, bioremediation may require that organisms are altered in some way to make
them more suitable for the task and this topic is addressed in Chapter 9. Briefly,
the pathways may be expanded by adaptation to the new molecule, or very much
less commonly, wholescale insertion of ‘foreign’ genes may occur by genetic
manipulation. There have been several cases reported where catabolic pathways
have been expanded in the laboratory. Hedlund and Staley (2001) isolated a strain
ofVibrio cyclotrophicusfrom marine sediments contaminated with creosote. By
supplying the bacteria with only phenanthrene as a carbon and energy source,
the bacteria were trained to degrade several PAHs although some of these only
by cometabolism with a supplied carbon source.
Endocrine disrupters
To date, there are chemicals, including xenobiotics, which still resist degradation
in the environment. This may be due to a dearth, at the site of contamination, of
organisms able to degrade them fully or worse, microbial activity which changes
them in such a way that they pose a bigger problem than they did previously. One
such example is taken from synthetic oestrogens such as 17α-ethinyloestradiol
commonly forming the active ingredient of the birth control pills, and the nat-
ural oestrogens which, of course, are not xenobiotics. Natural oestrogens are
deactivated in humans by glucuronidation, as shown in Figure 3.1, which is a
conjugation of the hormone with UDP-glucuronate making the compound more
Figure 3.1 Glucuronidation