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Iron oxide and hydroxides can be precipitated from solution with both [Fe.sup.2+] and [Fe.sup.2+] states by a microbial consortium enriched from surface water draining a granitic batholith. The [Fe.sup.2+]/[Fe.sup.3+] ratio of the microbial precipitate is determined by both the initial environment and subsequent diagenesis. To evaluate the thermal aspects of diagenesis, biological precipitates, either largely [Fe.sup.2+] or equally divided between [Fe.sup.2+] and [Fe.sup.3+] states, were heated at 80 [degrees] C for 12 weeks, under various redox conditions and compared to samples maintained under the same conditions at 4 [degrees] C. Mossbauer spectroscopy showed the iron oxide and hydroxides precipitated as [Fe.sup.2+] to be more stable than that as [Fe.sup.3+]. Only under air at 80 [degrees] C are the ferrous minerals altered to hematite, while the more labile ferric minerals are altered to Fe[(OH).sub.2] at 4 [degrees] C and to hematite at 80 [degrees] C. In contrast, chemically precipitated Fe compounds, when incubated with the consortium, only form [Fe.sup.3+] compounds, mainly fine-grained hematite. When no microbes are present, goethite is formed during diagenesis. Fe speciation in sediments may reflect a combination of microbial mediation that causes the initial precipitation of iron oxides and hydroxides and the subsequent conditions of the diagenetic processes characteristic of that particular depositional environment.

Iron oxide and hydroxides can be precipitated from solution with both [Fe.sup.2+] and [Fe.sup.2+] states by a microbial consortium enriched from surface water draining a granitic batholith. The [Fe.sup.2+]/[Fe.sup.3+] ratio of the microbial precipitate is determined by both the initial environment and subsequent diagenesis. To evaluate the thermal aspects of diagenesis, biological precipitates, either largely [Fe.sup.2+] or equally divided between [Fe.sup.2+] and [Fe.sup.3+] states, were heated at 80 [degrees] C for 12 weeks, under various redox conditions and compared to samples maintained under the same conditions at 4 [degrees] C. Mossbauer spectroscopy showed the iron oxide and hydroxides precipitated as [Fe.sup.2+] to be more stable than that as [Fe.sup.3+]. Only under air at 80 [degrees] C are the ferrous minerals altered to hematite, while the more labile ferric minerals are altered to Fe[(OH).sub.2] at 4 [degrees] C and to hematite at 80 [degrees] C. In contrast, chemically precipitated Fe compounds, when incubated with the consortium, only form [Fe.sup.3+] compounds, mainly fine-grained hematite. When no microbes are present, goethite is formed during diagenesis. Fe speciation in sediments may reflect a combination of microbial mediation that causes the initial precipitation of iron oxides and hydroxides and the subsequent conditions of the diagenetic processes characteristic of that particular depositional environment.

We report the detection of living colonies of nano-organisms (nanobes) on Triassic and Jurassic sandstones and other substrates. Nanobes have cellular structures that are strikingly similar in morphology to Actinomycetes and fungi (spores, filaments, and fruiting bodies) with the exception that they are up to 10 times smaller in diameter (20 nm to 1.0 [[micro]meter]). Nanobes are noncrystalline structures that are composed of C, O, and N. Ultra thin sections of nanobes show the existence of an outer layer or membrane that may represent a cell wall. This outer layer surrounds an electron dense region interpreted to be the cytoplasm and a less electron dense central region that may represent a nuclear area. Nanobes show a positive reaction to three DNA stains, [4[prime],6-diamidino-2 phenylindole (DAPI), Acridine Orange, and Feulgen], which strongly suggests that nanobes contain DNA. Nanobes are communicable and grow in aerobic conditions at atmospheric pressure and ambient temperatures. While morphologically distinct, nanobes are in the same size range as the controversial fossil nannobacteria described by others in various rock types and in the Martian meteorite ALH84001.

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 1 [[micro]meter]. 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.

Microbial mats on the surfaces of modern, marine stromatolites at Highborne Cay, Bahamas, were investigated to assess the role of microbial processes in stromatolite formation. The Highborne Cay stromatolitic mats contain Schizothix as the dominant cyanobacterium and show millimeter-scale lamination: Some layers in the mat are soft (unlithified), whereas other layers are crusty (lithified). Lithified layers within the mats correspond to micritic horizons composed of thin (20-50 [[micro]meter]) micritic crusts, which commonly overlie truncated, micritized carbonate sand grains. These features are identical to lithified laminae in the underlying stromatolite; the micritic crusts are similar in thickness to micritic laminae in many ancient stromatolites. Biogeochemical parameters in a representative stromatolitic mat from Highborne Cay were measured to identify the role of bacteria in precipitation and dissolution of CaC[O.sub.3]. Depth distributions of [O.sub.2], H[S.sup.-], and pH were determined with microelectrode measurements in the field. Oxygen profiles were used to calculate photosynthesis and aerobic respiration. Sulfate reduction was determined using 35S[O.sub.[4.sup.2-]] and sulfide oxidation potential was measured in homogenized samples. Our results indicate that cyanobacterial photosynthesis, sulfate reduction, and anaerobic sulfide oxidation in stromatolitic mats at Highborne Cay are responsible for CaC[O.sub.3] precipitation, whereas aerobic respiration and aerobic sulfide oxidation cause CaC[O.sub.3] dissolution. A close coupling of photosynthesis and aerobic respiration in the uppermost few millimeters of the mats results in no, or very little, net lithification. Sulfur cycling, on the other hand, shows a close correlation with the formation of lithified micritic layers. Photosynthesis, combined with sulfate reduction and sulfide oxidation results in net lithification. Sulfate reduction rates are high in the uppermost lithified layer and, on a diel basis, consume 33-38% of the C[O.sub.2] fixed by the cyanobacteria. In addition, this lithified layer contains a significant population of sulfide-oxidizing bacteria and shows a high sulfide oxidation potential. These findings argue that photosynthesis coupled to sulfate reduction and sulfide oxidation is more important than photosynthesis coupled to aerobic respiration in the formation of lithified micritic laminae in Highborne Cay stromatolites.

Microbiologic reduction of synthetic and geologic [Fe.sup.3+] oxides associated with four Pleistocene-age, Atlantic coastal plain sediments was investigated using a dissimilatory Fe reducing bacterium (Shewanella putrefaciens, strain CN32) in bicarbonate buffer. Experiments investigated whether phosphate and anthraquinone-2, 6-disulfonate, (AQDS, a humic acid analogue) influenced the extent of crystalline [Fe.sup.3+] oxide bioreduction and whether crystalline [Fe.sup.3+] oxides in geologic materials are more or less reducible than comparable synthetic phases. Anaerobic incubations ([10.sup.8] organisms/mL) were performed both with and without P[O.sub.4] and AQDS that functions as an electron repository and shuttle. The production of [Fe.sup.2+] (solid and aqueous) was followed with time, as was mineralogy by X-ray diffraction. The synthetic oxides were reduced in a qualitative trend consistent with their surface area and free energy: hydrous ferric oxide (HFO)>goethite>hematite. Bacterial reduction of the crystalline oxides was incomplete in spite of excess electron donor. Biogenic formation of vivianite [[Fe.sub.3][(P[O.sub.4]).sub.2][center dot]8[H.sub.2]O] and siderite (FeC[O.sub.3]) was observed; the conditions of their formation was consistent with their solubility. The geologic [Fe.sup.3+] oxides showed a large range in reducibility, approaching 100% in some materials. The natural oxides were equally or more reducible than their synthetic counterparts, in spite of association with non-reducible mineral phases (e.g., kaolinite). The reducibility of the synthetic and geologic oxides was weakly effected by P[O.sub.4], but was accelerated by AQDS. CN32 produced the hydroquinone form of AQDS (AHDS), that, in turn, had thermodynamic power to reduce the [Fe.sup.3+] oxides. As a chemical reductant, it could reach physical regions of the oxide not accessible by the organism. Electron microscopy showed that crystallite size was not the primary factor that caused differences in reducibility between natural and synthetic crystalline [Fe.sup.3+] oxide phases. Crystalline disorder and microheterogeneities may be more important.

We report the detection of living colonies of nano-organisms (nanobes) on Triassic and Jurassic sandstones and other substrates. Nanobes have cellular structures that are strikingly similar in morphology to Actinomycetes and fungi (spores, filaments, and fruiting bodies) with the exception that they are up to 10 times smaller in diameter (20 nm to 1.0 [[micro]meter]). Nanobes are noncrystalline structures that are composed of C, O, and N. Ultra thin sections of nanobes show the existence of an outer layer or membrane that may represent a cell wall. This outer layer surrounds an electron dense region interpreted to be the cytoplasm and a less electron dense central region that may represent a nuclear area. Nanobes show a positive reaction to three DNA stains, [4[prime],6-diamidino-2 phenylindole (DAPI), Acridine Orange, and Feulgen], which strongly suggests that nanobes contain DNA. Nanobes are communicable and grow in aerobic conditions at atmospheric pressure and ambient temperatures. While morphologically distinct, nanobes are in the same size range as the controversial fossil nannobacteria described by others in various rock types and in the Martian meteorite ALH84001.

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 1 [[micro]meter]. 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.

Microbial mats on the surfaces of modern, marine stromatolites at Highborne Cay, Bahamas, were investigated to assess the role of microbial processes in stromatolite formation. The Highborne Cay stromatolitic mats contain Schizothix as the dominant cyanobacterium and show millimeter-scale lamination: Some layers in the mat are soft (unlithified), whereas other layers are crusty (lithified). Lithified layers within the mats correspond to micritic horizons composed of thin (20-50 [[micro]meter]) micritic crusts, which commonly overlie truncated, micritized carbonate sand grains. These features are identical to lithified laminae in the underlying stromatolite; the micritic crusts are similar in thickness to micritic laminae in many ancient stromatolites. Biogeochemical parameters in a representative stromatolitic mat from Highborne Cay were measured to identify the role of bacteria in precipitation and dissolution of CaC[O.sub.3]. Depth distributions of [O.sub.2], H[S.sup.-], and pH were determined with microelectrode measurements in the field. Oxygen profiles were used to calculate photosynthesis and aerobic respiration. Sulfate reduction was determined using 35S[O.sub.[4.sup.2-]] and sulfide oxidation potential was measured in homogenized samples. Our results indicate that cyanobacterial photosynthesis, sulfate reduction, and anaerobic sulfide oxidation in stromatolitic mats at Highborne Cay are responsible for CaC[O.sub.3] precipitation, whereas aerobic respiration and aerobic sulfide oxidation cause CaC[O.sub.3] dissolution. A close coupling of photosynthesis and aerobic respiration in the uppermost few millimeters of the mats results in no, or very little, net lithification. Sulfur cycling, on the other hand, shows a close correlation with the formation of lithified micritic layers. Photosynthesis, combined with sulfate reduction and sulfide oxidation results in net lithification. Sulfate reduction rates are high in the uppermost lithified layer and, on a diel basis, consume 33-38% of the C[O.sub.2] fixed by the cyanobacteria. In addition, this lithified layer contains a significant population of sulfide-oxidizing bacteria and shows a high sulfide oxidation potential. These findings argue that photosynthesis coupled to sulfate reduction and sulfide oxidation is more important than photosynthesis coupled to aerobic respiration in the formation of lithified micritic laminae in Highborne Cay stromatolites.

Microbiologic reduction of synthetic and geologic [Fe.sup.3+] oxides associated with four Pleistocene-age, Atlantic coastal plain sediments was investigated using a dissimilatory Fe reducing bacterium (Shewanella putrefaciens, strain CN32) in bicarbonate buffer. Experiments investigated whether phosphate and anthraquinone-2, 6-disulfonate, (AQDS, a humic acid analogue) influenced the extent of crystalline [Fe.sup.3+] oxide bioreduction and whether crystalline [Fe.sup.3+] oxides in geologic materials are more or less reducible than comparable synthetic phases. Anaerobic incubations ([10.sup.8] organisms/mL) were performed both with and without P[O.sub.4] and AQDS that functions as an electron repository and shuttle. The production of [Fe.sup.2+] (solid and aqueous) was followed with time, as was mineralogy by X-ray diffraction. The synthetic oxides were reduced in a qualitative trend consistent with their surface area and free energy: hydrous ferric oxide (HFO)>goethite>hematite. Bacterial reduction of the crystalline oxides was incomplete in spite of excess electron donor. Biogenic formation of vivianite [[Fe.sub.3][(P[O.sub.4]).sub.2][center dot]8[H.sub.2]O] and siderite (FeC[O.sub.3]) was observed; the conditions of their formation was consistent with their solubility. The geologic [Fe.sup.3+] oxides showed a large range in reducibility, approaching 100% in some materials. The natural oxides were equally or more reducible than their synthetic counterparts, in spite of association with non-reducible mineral phases (e.g., kaolinite). The reducibility of the synthetic and geologic oxides was weakly effected by P[O.sub.4], but was accelerated by AQDS. CN32 produced the hydroquinone form of AQDS (AHDS), that, in turn, had thermodynamic power to reduce the [Fe.sup.3+] oxides. As a chemical reductant, it could reach physical regions of the oxide not accessible by the organism. Electron microscopy showed that crystallite size was not the primary factor that caused differences in reducibility between natural and synthetic crystalline [Fe.sup.3+] oxide phases. Crystalline disorder and microheterogeneities may be more important.