Environmental Engineering Reference
In-Depth Information
environmental sequences, such as genera
Sulfurovum
and
Sulfurimonas,
which
were found to be mesophilic chemolithoautotrophic SOB [19, 21].
Our results clearly indicate that these bacterial communities are quite similar
to the extant communities occurring at the anaerobic cold and/or methane seep
environments. The prokaryotic community on the seafloor might shift according
to the environmental change. The OAE layers contain globular or framboidal
metal sulfides thought to be produced by microbial activities of the SRB during
sedimentation and diagenesis [5], which is consistent with our observation of the
SRB dominance in the OAE black layer [20]. Although Kuypers [30] reported
that archaeal lipids dominated in the OAE1b layer, we were not successful
in obtaining archaeal DNA signals, even when using nested-PCR methods
[20].
We had no success in cultivation efforts from any of the OAE samples. To
some extent this is good news in terms of thinking about the paleome concept.
It would appear that the samples were not tainted by contaminants (which grew
readily from the drilling fluid and adjacent soils), and thus might be candidates
for a paleome, whose signals in the form of amplifiable DNA fragments were
still intact. While this is not truly ancient in geological terms, it is an interesting
and hopeful start in terms of our search for useful 'paleomes'.
4. CONCLUSION: LETTERS FROM ANCIENT
EARTH
In this chapter we have reviewed the evidence for the existence of unusual
molecular signals retrieved from a variety of subsurface environments. Some
of these cases would appear to be explained only by the long-term preserva-
tion of buried prokaryotic cells and/or their nucleic acids. In cases such as
the terrestrial deep subsurface, where nutrient-containing groundwater flows
through the environment, it may well be that active communities exist. How-
ever, in the marine subsurface, where nutrients arrive in much less abundance,
the activities, as reported by D'Hondt [9] are extremely low. Thus we have the
dilemma that the youngest sediments, i.e., those in the deep sea formed from
the spreading centers, are those most likely to have the least input of nutrients
and contamination. As they age, it is presumably a good place to “store” the
genetic knowledge of the past. However, as these sediments are uplifted and
become part of the continental mass, they become subject to the vagaries of
nutrient and ground-water input, making it more difficult to substantiate just
where the material arose that is being sampled. Thus it would appear that marine
sediments might represent good reservoirs of prokaryotic biomass occurring
at the shallow sediments near the seafloor. One might thus imagine that such
sediments and the genetic records they contain could be used to gain insight
into issues such as the co-evolution of Earth and microbial ecosystems. How-
