Fundamentals of Biological Intervention - Environmental Biotechnology: Theory and Application - page 53

in salty conditions, unprotected cells rapidly lose water from their cytoplasm
and dehydrate. Halophilic microbes appear to deal with this problem by ensuring
that their cytoplasm contains a higher solute concentration than is present in
their surroundings. They seem to achieve this by two distinct mechanisms, either
manufacturing large quantities of solutes for themselves or concentrating a solute
extracted from external sources. A number of species, for example accumulate
potassium chloride (KCl) in their cytoplasm, with the concomitant result that
extremozymes isolated from these organisms will only function properly in the
presence of high KCl levels. By the same token, many surface structural proteins
in halophiles require severely elevated concentrations of sodium salts.
Acidophiles thrive in the conditions of low pH, typically below 5, which occur
naturally as a result of sulphurous gas production in hydrothermal vents and
may also exist in residual spoils from coal mining activity. Though they can
tolerate an externally low pH, an acidic intra-cellular environment is intolerable
to acidophilic organisms, which rely on protective molecules in, or on, their cell
walls, membranes or outer cell coatings to exclude acids. Extremozymes capable
of functioning below pH 1 have been isolated from these structures in some
acidophile species.
At the other end of the spectrum, alkaliphiles are naturally occurring species
which flourish in soda lakes and heavily alkaline soils, typically enduring pH 9 or
more. Like the previous acidophiles, alkaliphiles require more typically neutral
internal conditions, again relying on protective chemicals on or near their surfaces
or in their secretions to ensure the external environment is held at bay.
Diverse degradative abilities
Bacteria possessing pathways involved in the degradation of a number of organic
molecules of industrial importance have been acknowledged for some time. One
oft quoted example is that for toluene degradation in Pseudomonas putida ,which
exhibits a fascinating interplay between the genes carried on the chromosome and
the plasmids (Burlage, Hooper and Sayler, 1989). When a new class of biopoly-
mer produced by the bacterium, Ralstonia eutropha , containing sulphur in its
backbone, was identified Lutke-Eversloh et al . (2001), it opened up the renewed
possibility of other novel biopolymers awaiting discovery, that might have
innovative and exciting applications in clean technology. Thus, bacteria are con-
stantly being discovered which exhibit pathways involved in the degradation and
synthesis of chemicals of particular interest to environmental biotechnologists.
Within the last ten years, a spate of bacteria representing very diverse degrada-
tive abilities have been discovered in a variety of niches adding almost daily, to
the pool of organisms of potential use to environmental biotechnology. By illus-
tration these include, phenol degrading Oceanomonas baumannii isolated from
estuarine mud from the mouth of the River Wear, UK (Brown, Sutcliffe and
Cummings, 2001), chloromethane utilising Hyphomicrobium and Methylobac-
terium from polluted soil near a petrochemical factory in Russia (McDonald
et al ., 2001) and a strain of Clostridium able to degrade cellulose, isolated from