THE PALEOME: LETTERS FROM ANCIENT EARTH - Past and Present Water Column Anoxia - page 29

Figure 4. Onboard microscopic observations of anaerobic thermophilic spore-forming fer-
menters isolated from deep subseafloor sediments in the Peru Margin, ODP Leg 201. (A) Cell
images on the optical microscopy. (B) DAPI-stained cells. (C) Cells hybridized by a specific
probe for the domain Bacteria (BAC338) by FISH method. Bar=1 µm.
3. PALEOMES IN THE TERESTRIAL SUBSURFACE
The terrestrial subsurface offers an interesting and different environment
from that seen in the marine subsurface. In general, these environments are
older and more geologically “mature” than the young crustal environments
of the marine system. Also, because of the nature of the hydrological cycle
and groundwater flow, they are often impacted by subsurface water flowing
from land to sea across the samples. Thus, while many of these environments
originated with oceanic populations and processes, they are often strongly
impacted by terrestrial contamination in the form of freshwater, nutrients, and
biomass. Contamination that makes the interpretation of results even more
problematic than the marine subsurface samples discussed above.
3.1 Molecular Signals from Terrestrial Tunneled
Subsurface Environments
One of the prevalent examples of the terrestrial subsurface is that provided
by deep subsurface tunnels drilled for various uses, usually mining for metals.
Such mines provide easy access to the deep subsurface microbial habitat. In
the past decade extensive surveys for microbial habitats in global deep subsur-
face environments beneath such tunneled environments have clearly demon-
strated the existence of life in global deep subsurface was evidenced (e.g.
[12, 26, 40, 46]). Most living microorganisms in deep subsurface environments
are of course adapting to the ambient geochemical characteristics. For exam-
ple, Thermus sp. found in a South African Gold mine was able to grow under
anaerobic conditions using iron and manganese as electron acceptors for respi-
ratory metabolism [26]. One of the most alkaliphilic microorganisms known,
Alkaliphilus transvaalensis (optimum pH = 10.0, maximum pH = 12.5), was
isolated from a deep subsurface environment of the South African gold mine at
the depth of 3,200 m below land surface [47], a source that has many geological
and geophysical similarities to the deep subsurface.