Fundamentals of Biological Intervention - Environmental Biotechnology: Theory and Application - page 58

known to be able to degrade PAHs and a novel strain of Vibrio cyclotrophicus
able to digest naphthalene and phenanthrene, has been isolated from creosote
contaminated marine sediments from Eagle Harbour, Washington, USA. It would
appear that bacteria isolated from the same marine or estuarine environments may
vary quite considerably in their abilities to degrade certain PAHs. This observa-
tion is viewed as indicative of diverse catabolic pathways demonstrated 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, although a strain of Pseudomonas putida , that is able to degrade PCBs
has been isolated from waste water outflow from a refinery. This was achieved by
the bacterium employing two pathways encoded by two separate operons; the tod
pathway employed in toluene degradation, and the cmt pathway which normally
is responsible for the catabolism of p -cumate which is a substituted toluene. The
mutation which allowed this strain to utilise the cmt pathway 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 conjunc-
tion with each other to metabolise PCBs, a relationship described as mosaic
(Ohta et al ., 2001).
The pthalates are substituted single ring phenols and include terephthalic acid
and its isomers, the major chemicals used in the 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. Analysis of anaerobic sewage sludge has revealed a methanogenic
consortium of over 100 bacterial clones with the capability to digest terephtha-
late. Characterisation of these by analysis of their ribosomal DNA sequences,
revealed that almost 70% were archaeans, most of which had not been previ-
ously identified, and that nearly 90% of the total bacteria comprised two of the
novel archaean species. These two species believed to be responsible for the
degradation of terephthalic acid (Wu et al ., 2001). 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 topic, reference is made to the movement of genes within and
between organisms. The reason why it appears at all in a topic on environ-
mental biotechnology is to emphasise the 'oneness' of the environment, not just
at the more obvious level of industrial impact but right down to the interac-
tion between the genetic material of organisms themselves. Plasmids may be
transferred between bacteria by conjugation of which there are several types,
but all of which require direct cell to cell contact. Not only are genes trans-
ferred between bacteria on plasmids, but bacteriophages (bacterial viruses) are