Da. Brown et al., MINERALS ASSOCIATED WITH BIOFILMS OCCURRING ON EXPOSED ROCK IN A GRANITIC UNDERGROUND RESEARCH LABORATORY, Applied and environmental microbiology, 60(9), 1994, pp. 3182-3191
The concept of disposal of nuclear fuel waste in crystalline rock requ
ires the effects of microbial action to be investigated. The Undergrou
nd Research Laboratory excavated in a pluton of the Canadian Shield pr
ovides a unique opportunity to study these effects, Three biofilms kep
t moist by seepage through fractures in granitic rock faces of the Und
erground Research Laboratory have been examined. The biofilms containe
d a variety of gram-negative and gram-positive morphotypes held togeth
er by an organic extracellular matrix. Nutrient levels in the groundwa
ter were low, but energy dispersive X-ray spectroscopy has shown bioge
ochemical immobilization of several elements in the biofilms; some of
these elements were concentrated from extremely dilute environmental c
oncentrations, and all elements were chemically complexed together to
form amorphous or crystalline fine-grained minerals. These were seen b
y transmission electron microscopy to be both associated with the surf
aces of the bacteria and scattered throughout the extracellular matrix
, suggesting their de novo development through bacterial surface-media
ted nucleation. The biofilm consortia are thought to concentrate eleme
nts both by passive sorption and by energy metabolism. By Mossbauer sp
ectroscopy and X-ray diffraction, one of the biofilms showed that iron
was both oxidized and precipitated as ferrihydrite or hematite aerobi
cally and reduced and precipitated as siderite anaerobically. We belie
ve that some Archean banded-iron formations could have been formed in
a manner similar to this, as it would explain the deposition of hemati
te and siderite in close proximity. This biogeochemical development of
minerals may also affect the transport of material in waste disposal
sites.