22 Environmental Biotechnology
accepted is based on the sequence of the DNA coding for ribosomal RNA,
the rDNA (Stackebrandt and Woese 1981). For completeness, it is important
to mention the retroviruses which are a group of eukaryotic viruses with RNA
rather than DNA as their genome. They carry the potential for integration into
inheritable DNA due to the way in which they replicate their genomic RNA by
way of a DNA intermediate.
Microbial diversity
Microbes have been discovered in extraordinarily hostile environments where
their continued survival has made demands on their structure and metabolic capa-
bility. These organisms, frequently members of the archaea, are those which have
the capacity to degrade some of the most hazardous and recalcitrant chemicals
in our environment and thus provide a rich source of metabolic capacity to deal
with some very unpleasant contaminants. This situation will remain as long as the
environments which harbour these invaluable microbes are recognised as such
and are not destroyed. Microbial life on this planet, taken as a whole, has an
immense capability to degrade noxious contaminants; it is essential to maintain
the diversity and to maximise the opportunity for microbes to metabolise the
offending carbon source.
Metabolic Pathways of Particular Relevance to Environmental
Biotechnology
Having established that the overall strategy of environmental biotechnology is
to make use of the metabolic pathways in micro-organisms to break down or
metabolise organic material, this chapter now examines those pathways in some
detail. Metabolic pathways operating in the overall direction of synthesis are
termed anabolic while those operating in the direction of breakdown or degrada-
tion are described as catabolic: the terms catabolism and anabolism being applied
to describe the degradative or synthetic processes respectively.
It has been mentioned already in this chapter and it will become clear from
the forthcoming discussion, that the eventual fate of the carbon skeletons of
biological macromolecules is entry into the central metabolic pathways.
Glycolysis
As the name implies, glycolysis is a process describing the splitting of a phosphate
derivative of glucose, a sugar containing six carbon atoms, eventually to produce
two pyruvate molecules, each having three carbon atoms. There are at least four
pathways involved in the catabolism of glucose. These are the Embden–Meyerhof
(Figure 2.1), which is the one most typically associated with glycolysis, the Ent-
ner–Doudoroff and the phosphoketolase pathways and the pentose phosphate