Environmental Engineering Reference
In-Depth Information
Our studies have focused on the distribution and phylogenetic diversities of
microbial communities occurring at deep terrains in the Hishikari gold mine,
located at the southern part of Kyushu Island in Japan. This mine is the ep-
ithermal type-gold mine associated with a geothermal activity of the Kirishima
volcano and contains the most productive gold-silver deposits in the west-
ern Pacific Margin. The basement of the Hishikari gold mine is composed of
shales of oceanic sediments formed at the Cretaceous period called 'Shimanto-
Supergroup' [18]. The analyses of deuterium-oxygen isotopes suggested that
the subground hot aquifer water was circulated meteoric water [33]. Thus, this
environment is similar to many other mines: an ancient geologic setting im-
pacted by modern aquifers and the organisms that adapt within them. Such an
environment makes the concept of the “paleome” a difficult one to substantiate
because of the opportunity for present day growth of microbial communities.
Using molecular genetic analyses, we determined that the predominant or-
ganisms were related to previously uncultivated bacteria of the order
Aquificales
[18]. Further work resulted in the cultivation of some of these bacteria [48], one
of which was named
Sulfurihydrogenobium subterraneum
[49], and was found
to be able to use various gases and geochemical components dissolved in the
hot deep aquifer as electron donors and/or acceptors and to grow chemolithoau-
totrophically. In the same environment, we also isolated a variety of members
related to known genera
Hydrogenophilus
,
Azoarcus
,
Thermus
, and to not-yet-
known novel species. For example,
Thermus
sp. closely related to that of
T.
scotoductus
, was found to be capable of anaerobic growth using nitrate and
ferrihydrite as an electron acceptor. The physiological properties of
Thermus
and other isolates from the subsurface biosphere of the Hishikari gold mine
leave us with a similar message from other tunneled environments, namely
that the microbial population is adapting to and reflective of the surrounding
geochemical settings.
Given these results, it is hard to consider the endemic populations in the deep
mines as a paleome so much as active populations adapting to and growing in
the subsurface. However, in addition to the above results, culture-independent
molecular ecological surveys of subsurface terrestrial environments have re-
vealed a variety of prokaryotes inhabiting the aquifers and rocks, including
unexpected signatures that are not consistent with the current subsurface envi-
ronment. For example, unusual archaeal phylotypes have been obtained from
fissure water samples that were related to the hyperthermophilic Archaea
Pyro-
coccus
and other yet uncultivated, novel Archaea [46]. These results suggested
that these molecular signatures might be derived from more deep anaerobic,
