『Abstract
Mineral dissolution experiments using batch cultures of soil
and groundwater bacteria were monitored with solution chemistry
and various microscopic techniques to determine the effects of
these organisms on weathering reactions. Several strains of bacteria
produced organic and inorganic acids and extracellular polymers
in culture, increasing the release of cations from biotite (Si,
Fe, Al) and plagioclase feldspar (Si, Al) by up to two orders
of magnitude compared to abiotic controls. Microbial colonies
on mineral grains were examined by cryo-scanning electron microscopy
(cryo-SEM), confocal scanning laser microscopy (CSLM), and epifluorescence
microscopy. Bacteria colonized all mineral surfaces, often preferentially
along cleavage steps and edges of mineral grains. Low-voltage
high-resolution cryo-SEM of high-pressure cryofixed and partially
freeze-dried colonized minerals showed many bacteria attached
by extracellular polymers of unknown composition. These biofilms
covered much larger areas of the mineral surfaces than bacterial
cells alone. Mineral surfaces where bacteria and extracellular
polymers occurred appeared more extensively etched than surrounding
uncolonized surfaces. CSLM was used to observe microbial colonization
of biotite and to measure pH in microenvironments surrounding
living microcolonies using a ratiometric pH-sensitive fluorescent
dye set. A strain of bacteria (B0693 from the U.S. Department
of Energy Subsurface Microbial Culture Collection) formed large
attached microcolonies, both on the outer (001) surface and within
interlayer spaces as narrow as 1μm. Solution pH decreased from
near neutral at the mineral surface to 3-4 around microcolonies
living within confined spaces of interior colonized cleavage planes.
However, no evidence of pH microgradients surrounding exterior
microcolonies was noted.』
Introduction
Indirect biochemilithic mechanisms
Direct biochemilithic mechanisms
Methods
Rationale
Bacteria
Mineral preparation
Experiments
Epifluorescence microscopy
Cryomicroscopy
Quantitative confocal microscopy
Results
Solution chemistry
Cryomicroscopy
Quantitative confocal microscopy
Discussion
Acknowledgments
References cited