50 Environmental Biotechnology
the use of biological systems in environmental engineering relate to the nature
of the substances needing to be removed or treated and to the localised envi-
ronmental conditions pertaining to the particular situation itself. Thus, in respect
of the former, the intended target of the bioprocessing must generally be both
susceptible and available to biological attack, in aqueous solution, or at least
in contact with water, and within a low to medium toxicity range. Generally,
the local environmental conditions required would ideally offer a temperature
of 20–30◦C but a range of 0–50◦C will be tolerated in most cases, while an
optimum pH lies in the range 6.5–7.5, but again a wider tolerance of 5.0–9.0
may be acceptable, dependent on the precise organism involved. For land-based
applications, especially in the remediation of contamination or as a component of
integrated pollution control measures, there is an additional common constraint
on the substrate. Typically the soil types best suited to biotechnological inter-
ventions are sands and gravels, with their characteristically low nutrient status,
good drainage, permeability and aeration. By contrast, biological treatments are
not best suited to use in clays or peat or other soils of high organic content.
In addition, generalised nutrient availability, oxygenation and the presence of
other contaminants can all play a role in determining the suitability of biological
intervention for any given application.
Extremophiles
As has been previously mentioned, in general the use of biotechnology for envi-
ronmental management relies on mesophilic micro-organisms which have roughly
similar environmental requirements to ourselves, in terms of temperature, pres-
sure, water requirement and relative oxygenation. However, often some of their
abilities, which are directly instrumental in enabling their use in this context, arose
in the first instance as a result of previous environmental pressures in the species
(pre)history. Accordingly, ancient metabolic pathways can be very valuable tools
for environmental biotechnology. Thus, the selective advantages honed in Car-
boniferous coal measures and the Pleistocene tar pits have produced microbes
which can treat spilled mineral oil products in the present and methanogenesis, a
process developed by the Archae during the dawn of life on earth, remains rele-
vant to currently commonplace biological interventions. Moreover, some species
living today tolerate extreme environments, like high salinity, pressures and tem-
peratures, which might be of use for biotech applications requiring tolerance to
these conditions. The Archaea (the group formerly known as the archaebacte-
ria and now recognised as forming a distinct evolutionary line) rank amongst
their numbers extreme thermophiles and extreme halophiles in addition to the
methanogens previously mentioned. Other species tolerate high levels of ionis-
ing radiation, pH or high pressures as found in the deep ocean volcanic vents
known as ‘black smokers’.
Making use of these extremophile organisms could provide a way of develop-
ing alternative routes to many conventional chemicals or materials in such a way