F. G. Ferris

Diversity of iron and silica precipitation by microbial mats in hydrothermal waters, Iceland: Implications for Precambrian iron formations

Direct examination of microbial mats from Icelandic hot springs with transmission electron microscopy and energy-dispersive X-ray spectroscopy revealed a consortium of bacterial cells in varying stages of mineralization. Differences in observed mineralogy largelyreflectdifferencesinthechemistryofthehydrothermalwaters.Silica-richspheroids formedepicellularlyoncellwallsandsurroundingsheathsandcapsulesofmicroorganisms and,insomecases,intracellularlywhenpresumablythecell(s)hadlysed.Commonly,these precipitateswereobservedcoalescingtoformamatrixofamorphoussilicathatcompletely encapsulated the cells and/or replaced their cytoplasmic material. However, in other cells, the precipitates were composed of amorphous granules made exclusively of iron and silica inapproximatelyequalproportions.Atonelocality,thebacteriaformedseveralepicellular iron minerals, ranging from iron-mineralized capsules tofine-grained spheroids of amorphous ferric hydroxide and acicular aggregates of goethite. The complete encrustation of bacterial cells by silica, iron, or a combination of both may greatly enhance their preservation potential, such that these mineralized microorganisms may conceivably represent future microfossils. Thus, we may be witnessing contemporaneous biomineralization processes that are similar to those of the geologic past, particularly with regard to the origin of some Precambrian banded iron formations.

Characterization of Bacteriogenic Iron Oxide Deposits from Axial Volcano, Juan de Fuca Ridge, Northeast Pacific Ocean

Iron oxides from the caldera of Axial Volcano, a site of hydrothermal vent activity along the Juan de Fuca Ridge, are characterized by abundant bacterial structures that closely resemble the sheaths of Leptothrix ochracea , the stalks of Gallionella ferruginea , and the filaments of a novel iron oxidizing PV-1 strain. These bacteria are commonly associated with iron-oxide precipitates and are proposed to play two causal roles in the formation of iron oxides at Axial Volcano. First, by increasing the rate of Fe 2+ oxidation, and second, by lowering the concentration of Fe 3+ required for precipitation by providing a reactive surface for heterogeneous nucleation. Rapid rates of oxidation and precipitation caused by the bacteria likely contribute to the poorly ordered nature of the iron oxides, determined to be primarily 2-line ferrihydrite, and in one case, poorly ordered goethite. The iron-oxide precipitates consist dominantly of iron, silicon (mostly diatoms), and organic carbon with a suite of sorbed trace metals. The high metal uptake affinity of these poorly ordered iron oxides may be important in the global cycling of trace elements throughout the worlds oceans. Additionally, iron oxides precipitating on the surface of bacteria can preserve individual cells as microfossils making bacteriogenic iron oxides ideal proxies for paleoenvironmental and astrobiological studies.

Accumulation of Metals by Bacteriogenic Iron Oxides in a Subterranean Environment

Bacteriogenic iron oxides (BIOS) and groundwater samples were collected from 66 to 432 m underground at the Aspo Hard Rock Laboratory near Oskarshamn, Sweden. The twisted, iron oxide-encrusted stalks of the lithoautotrophic ferrous iron-oxidizing bacterium Gallionella ferruginea were prominent in the BIOS samples. A wide variety of heterotrophic bacteria, including stalked forms resembling Caulobacter or Hyphomicrobium species, were also present. Energy dispersive x-ray spectroscopy, selected area electron diffraction, and x-ray diffraction analyses confirmed that the BIOS samples contained only poorly ordered (amorphous) hydrous ferric oxide. Inductively coupled plasma emission spectroscopy revealed iron oxide contents that varied from 60% to 90% (dry weight basis). Metal concentrations in filtered groundwater ranged from 10mM for Na to 10 -4 mM or less for Co, Cu, Cr, and Zn. Intermediate concentrations were recorded for Fe and Mn ( 10 -2mM). Solid-phase metal concentrations in the BIOS spanned the 10 -...

Precipitation of carbonate minerals by microorganisms: Implications for silicate weathering and the global carbon dioxide budget

Direct light and electron microscopic studies show that cyanobacterial cells serve as nucleation sites for carbonate mineral precipitation in a variety of fresh to saline‐alkaline lakes on the Cariboo Plateau in central British Columbia, Canada, and in mineralized crusts on weathered basalt in Iceland. The carbonate minerals found in association with the cyanobacteria were extremely fine‐grained, and invariably occurred on the external surfaces of the cells. Carbonate mineralogy was variable, ranging from calcite to magnesite, depending on differences in lake and groundwater chemistry (i.e., saturation state of the water with respect to individual carbonate minerals). In microcosm experiments, phototrophic cyanobacterial growth increased alkalinity and the degree of oversaturation with respect to calcite. Calculated values for the saturation state of calcite and magnesite in Cariboo Plateau natural waters exhibited two distinct trends, with (1) high magnesite saturation values in areas where the weatherin...

Biogeochemical Properties of Bacteriogenic Iron Oxides

Bacteriogenic iron oxides (BIOS) are composite materials that consist of intact and partly degraded remains of bacterial cells intermixed with variable amounts of poorly ordered hydrous ferric oxide (HFO) minerals. They form in response to chemical or bacterial oxidation of Fe2+, which gives rise to Fe3+. Once formed, Fe3+ tends to undergo hydrolysis to precipitate in association with bacterial cells. In acidic systems where the chemical oxidation of Fe2+ is slow, bacteria are capable of accelerating the reaction by several orders of magnitude. At circumneutral pH, the chemical oxidation of Fe2+ is fast. This requires Fe2+ oxidizing bacteria to exploit steep redox gradients where low pO2 slows the abiotic reaction enough to allow the bacteria to compete kinetically. Because of their reactive surface properties, BIOS behave as potent sorbents of dissolved metal ions. Strong enrichments of Al, Cu, Cr, Mn, Sr, and Zn in the solid versus aqueous phase (log 10 Kd values range from 1.9 to 4.2) are common; however, the metal sorption properties of BIOS are not additive owing to surface chemical interactions between the constituent HFO and bacteria. These interactions have been investigated using acid-base tritrations, which show that the concentration of high pKa sites is reduced in BIOS compared to HFO. At the same time, hydroxylamine insoluble material (i.e., residual bacterial fraction) is enriched in low pKa sites relative to both BIOS and HFO. These differences indicate that low pKa or acidic sites associated with bacteria in BIOS interact specifically with high pKa or basic sites on intermixed HFO.

Ultrastructure and potential sub-seafloor evidence of bacteriogenic iron oxides from Axial Volcano, Juan de Fuca Ridge, north-east Pacific Ocean

Iron oxides from the caldera of Axial Volcano, a site of hydrothermal vent activity along the Juan de Fuca Ridge, were found to consist predominantly of microbial structures in hydrated whole mounts examined using an environmental scanning electron microscope. Novel observations were made of the iron oxides revealing the spatial relationships of the bacteria within to be more consistent with microbial mats than mineral precipitates. The bacterial structures are attributed to the sheaths of Leptothrix ochracea, the stalks of Gallionella ferruginea, and the filaments of a novel iron oxidizing PV-1 strain, based on the distinctive morphological characteristics of these three bacteria. Energy dispersive X-ray spectroscopy revealed the presence and distribution of Fe, Si, and Cl on the bacterial sheaths, stalks and filaments. The iron oxides were identified by X-ray diffraction to be two-line ferrihydrite, a poorly ordered iron oxyhydroxide. Adsorption of Si in particular to two-line ferrihydrite likely contributes to its stability on the seafloor, and might also be a preservation mechanism creating microfossils of the bacterial structures encrusted with ferrihydrite. Presumptive evidence of the sub-seafloor presence of L. ochracea, G. ferruginea and PV-1 at Axial Volcano was obtained from the presence of these bacteria on a trap that had been placed within an active vent, and also in a vent fluid sample. If indeed these bacteria are present in the sub-seafloor, it may be an indication that the surface expression of iron oxide deposits at Axial Volcano is minimal in comparison to what exists beneath the seafloor.

Precipitation of iron, silica, and sulfate on bacterial cell surfaces

The present study documents the precipitation of Fe(III), silica, and sulfate in the presence of 3 different bacteria (Bacillus subtilus, Bacillus licheniformis, and Pseudomonas aeruginosa), under different total Fe(III) concentrations (10−2 M, 10−3 M, 10−4 M) at constant pH (4.0). Morphology and chemical composition of the precipitates were compared with those formed in abiotic control systems, while chemical composition and precipitation of the precipitates were modeled according to solution chemistry data. Transmission electron microscopy (TEM) observations showed morphological differences between the biotic and abiotic systems. All systems contained small grains (diam. 2–50 nm), but amorphous material (i.e., material without any specific morphology) and nodules were present only in the cell systems. This is because bacterial surfaces and exopolymers provided numerous binding sites for metal and anion sorption and promoted heterogeneous nucleation of hydrous ferric oxides (HFO). The initial Fe/Si and F...

Microbial precipitation of a strontium calcite phase at a groundwater discharge zone near rock Creek, British Columbia, Canada

Mineralogical, chemical, and microscopic analyses demonstrate an intimate relationship between epilithic cyanobacteria and the precipitation of a strontium calcite phase at a groundwater discharge zone located near Rock Creek, British Columbia, Canada. The groundwater flows out of a serpentinite bedrock outcrop that provides a hard surface for the accretion of a coherent calcareous crust. The mean pH of water samples collected ∼2.0 m above the base of the outcrop was 8.5, whereas a value of 8.8 was recorded for samples taken near the outcrop base. This increase in pH can be attributed to the growth of cyanobacteria that carry out a HCO3 ‐/OH‐ exchange process during photosynthesis. Calcium was present in the water samples at levels of 32–36 ppm, whereas strontium occurred at lower concentrations (5.8–6.6 ppm). In each case, the lowest calcium and strontium values occurred in samples taken near the base of the outcrop, as expected for carbonate mineral precipitation. The crust itself is a porous thrombolit...

Retention of Iodide by Bacteriogenic Iron Oxides

This study was performed to determine the ability of wetland bacteriogenic iron oxides (BIOS) to immobilize iodide in contaminated groundwater systems near Chalk River, Canada. The sorption of iodide onto synthetic hydrous ferric oxide (HFO) and BIOS was investigated using an autotitrator and an I− ion-selective electrode to generate high-resolution anion sorption data over a pH range of 2.5 to 9. The effect of strontium sorption in the presence of I− was also investigated to determine its effect on iodide retention as it is also a common contaminant near Chalk River. Both HFO and BIOS correspond to 2-line ferrihydrite with surface areas of 227.7 m2 g−1 and 92.52 m2 g−1, respectively. Sorption of I− was found to be pH dependent for both HFO and BIOS and was most strongly immobilized at pH 2.5. The pH at which 50% of the I− was bound to HFO occurred at pH 4.0, whereas BIOS maintained 50% sorption to pH 9. Field data also indicated a 54% decrease for iodine and 75% for 129I in waters passing over in-situ BIOS at circumneutral pH. Iodide sorption to HFO is best explained by homogeneous functional groups, whereas sorption of I− to BIOS is best explained by heterogeneous functional groups, due to the presence of bacterial functional groups with pKa values that extend to 9.0. The presence of Sr2+ decreased iodide sorption on HFO by 10–20%, but had no effect on BIOS due to its surface functional groups being reactive over the pH range investigated in this study. These results imply that BIOS is a useful sorbent for natural retention of I− from groundwater and that the amount of organic material present in iron oxides is an important factor when considering remediation strategies for radionuclides in groundwater.

Microbial communities in deep Canadian shield groundwaters—an in situ biofilm experiment

Microbial biofilm communities were cultivated on stainless steel and polypropylene surfaces within brine‐filled exploration boreholes in crystalline rocks of the Canadian Shield at Kidd Creek Mine (Timmins, Ontario) and Copper Cliff South Mine (Sudbury, Ontario) at depths of 1402 m and 1219 m, respectively. The calcium‐sodium‐chloride brines were acidic (pH 3.5–4.8) and had temperatures of 23.4°C to 18.6°C. Direct microscopic counts using DAPI (4’,6‐diamidino‐2‐phenylindole) epifluorescent staining revealed coccoid‐shaped, vibroid, rod‐shaped, and filamentous bacteria in Copper Cliff South biofilms. The same morphological types were observed at Kidd Creek with the addition of a group of large (2–3 μm in length) vibroid to rod‐shaped bacteria. Average total counts were 9 ±7 × 106 bacteria/cm2 for Copper Cliff South biofilms and 5 ± 1 × 106 bacteria/cm2 for Kidd Creek biofilms with a mean biomass value of 131 ± 35 μg carbohydrate/cm2. Transmission electron microscopy revealed slightly vibroid, rod‐shaped, g...