Environmental Engineering Reference
In-Depth Information
CHAPTER TEN
Diversity and evolution of micro-
organisms and pathways for the
degradation of environmental
contaminants: a case study with the
s-triazine herbicides
MICHAEL JAY SADOWSKY
Introduction
On 7 December 1854, Louis Pasteur is quoted as saying 'Dans les champs de
l'observation le hasard ne favorise que les esprits pr´par´s.' This statement,
which has been often translated as 'Chance favours the prepared mind', can,
after slight modification, also be applied to the interaction of micro-organisms
with anthropogenic growth substrates. Namely, that chance favours the pre-
pared bacterium! Given the strong selection pressure for growth of micro-
organisms in natural environments, microbial species that have the ability to
rapidly acquire new genes that allow them to utilise newly introduced anthro-
pogenic compounds gain a selective advantage for growth over others living
in the same environment. This may eventually lead to changes in microbial
populations and community structure over time.
While the evolution of microbial genes, and even pathways, for the catabol-
ism of novel compounds released into the environment was originally thought
to take long periods of time (on an evolutionary scale), recent evidence indi-
cates that microbes and their genomes are relatively plastic ( Jain et al.
2002
;
Mira et al.
2002
), and as such can evolve the ability to utilize new carbon and
energy sources in a relatively short time frame, from years to tens of years
(Seffernick & Wackett
2001
). This phenomenon has led to paradigm shifts in
the way in which we view microbial evolution and the potential impact of
anthropogenic perturbations on microbial processes. While several approaches
have been used to examine the evolution of bacterial genes and pathways for
substrate utilization, many have been rather artificial, using idealised growth
conditions, limited microbial diversity, specialised laboratory growth media,
chemostats and novel substrates with structural similarities to natural
