Researchers Find Glass-eating Microbes at the Rock Bottom of the Food Chain

A microscopic view of tubular structures in a 25-micrometer-thick, polished slice of brown volcanic "glass" (rock-like super-cooled lava). These tunnels are thought to be borings made by microbes deep inside the oceanic crust. The sample was taken from Ocean Drilling Project drill site 504B in the Eastern Equatorial Pacific, 375 meters into the oceanic crust (approximately 4,000 meters below sea level). A scanning electron microscope view of a "biofilm" covering a glass surface altered by microbial activity. Filaments of biological matter (F) are attached to fresh glass (FG). The sample was taken from Ocean Drilling Project drill site 410 in the North Atlantic, 25 meters into the oceanic crust (approximately 3,300 meters below sea level).

Welcome to the bottom of
the deep-sea food chain. The rock bottom, that is. In the current edition
of Geochemistry, Geophysics,
Geosystems, a team of researchers uncovers and characterizes
a process that is commonplace below the ocean bottom. In the upper 300
meters of the earth’s oceanic crust, microbes were found to have
literally eaten their way through rock. Traces of this process are preserved
in the glassy margins of underwater lava flows (scientists call super-cooled
lava spewed by undersea volcanoes "glass," which is similar
to material used to make stone-age axes and knives). Glass samples were
recovered by drilling as deep as four miles below sea level. "We’ve
documented how extensive
these microscopic organisms are eating into volcanic rock, leaving worm-like
tracks that look like someone has drilled their way in," said one
of the paper’s co-authors, Hubert Staudigel of Scripps Institution
of Oceanography at the University of California, San Diego. "Our
study has confirmed that there’s no place in the oceans that doesn’t
have these features." The process of volcanic rock changing from
one state to another has traditionally been seen as a purely chemical-physical
process, rather than biological. These rock alterations lead to chemical
interactions between the oceanic crust and seawater, influencing important
chemical cycles on the earth, including the carbon cycle that is important
to the earth’s climate.

Staudigel says the microbes
may tunnel their way into rock to derive chemical energy from the glass
and to find protection from larger grazing organisms. He calls the glass-eating
microbes the rock bottom of the food chain. "We’ve basically
determined the depth of the biosphere," said Staudigel. The study
is featured as an "Editor’s Choice" selection in the
September 28, 2001 edition of the journal Science. Co-authors
include Harald Furnes, Ingunn H. Thorseth, Terje Torsvik, and Ole Tumyr
of Bergen University in Norway, and Karlis Muehlenbachs of the University
of Alberta in Edmonton.

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