Fundamentals of Biological Intervention 59with offshore drilling, along with alkylphenols. Several genera of bacteria are
now known to be able to degrade PAHs and recently, a novel strain ofVib r io
cyclotrophicusable to digest naphthalene and phenanthrene, was isolated from
creosote-contaminated marine sediments from Eagle Harbour, Washington, USA.
It would appear that bacteria isolated from the same marine or estuarine envi-
ronments may vary quite considerably in their abilities to degrade certain PAHs.
This observation is viewed as indicative of diverse catabolic pathways demon-
strated by these organisms and awaiting our full understanding (Hedlund and
Staley 2001).
Polycyclic hydrocarbons (PCBs) are xenobiotics which, due to their high level
of halogenation, are substrates for very few pathways normally occurring in
nature. However, a strain ofPseudomonas putidaable to degrade PCBs, was
isolated recently from wastewater outflow from a refinery. This was achieved by
the bacterium employing two pathways encoded by two separate operons; thetod
pathway employed in toluene degradation, and thecmtpathway which normally
is responsible for the catabolism ofp-cumate which is a substituted toluene. The
mutation which allowed this strain to utilise thecmtpathway was found to be
a single base change to the promoter-operator sequence. This allowed all the
enzymes in this pathway to be expressed under conditions where their synthesis
would normally be repressed. Thus, the two pathways could work in conjunction
with each other to metabolise PCBs, a relationship described as mosaic (Ohta
et al2001).
The pthalates are substituted single-ring phenols and include terephthalic acid
and its isomers, the major chemicals used in manufacture of polyester fibres,
films, adhesives, coatings and plastic bottles. In Chapter 2, and earlier in this
chapter, homage has been paid to the resources of genetic capability exhibited by
the archaeans. In a recent analysis of anaerobic sewage sludge, a methanogenic
consortium of over 100 bacterial clones were found to have the capability to
digest terephthalate. Characterisation of these by analysis of their ribosomal DNA
sequences, revealed that almost 70% were archaeans most of which had not been
previously identified, and that nearly 90% of the total bacteria comprised two
of the novel archaean species. These two species are believed to be responsi-
ble for the degradation of terephthalic acid (Wuet al2001). During wastewater
treatment, terepthalic acid is usually treated by aerobic processes. However,
this consortium, or others like it provide an anaerobic alternative which, being
methanogenic, may be structured to offset processing costs by the utilisation of
the methane.
Mobility of DNA
Throughout this book, reference is made to the movement of genes within and
between organisms. The reason why it appears at all in a book on environmen-
tal biotechnology is to emphasise the ‘oneness’ of the environment, not just at
the more obvious level of industrial impact but right down to the interaction