Duckworth,O.W., Holmstrom(後のoの頭に¨),S.J.M., Pena(nの頭に〜),J. and Sposito,G.(2009): Biogeochemistry of iron oxidation in a circumneutral freshwater habitat. Chemical Geology, 260, 149-158.

『中性付近の淡水棲息地における鉄酸化の生物地球化学的性質』


Abstract
 Iron(II) oxidation in natural waters at circumneutral pH, often regarded as an abiotic process, is frequently biologically mediated at iron-rich redox gradients. West Berry Creek, a small circumneutral tributary that flows through a mixed coniferous forest in Big Basin State Park, California, contains localized iron (hydr)oxide precipitates at points along its course where anoxic groundwater meets oxygenerated creek water. These mixing zones establish redox gradients that may be exploited by microbes forming microbial mats that are intimately associated with iron (hydr)oxide precipitates. Water sampling revealed strong correlations between the concentrations of aqueous inorganic species, suggesting a rock-weathering source for most of these solutes. Liquid chromatography-electrospray ionization-mass spectrometry techniques detected significant concentrations of organic exudates, including low molecular mass organic acids and siderophores, indicating that active biogeochemical cycling of irons is occurring in the creek. X-ray diffraction and elemental analysis showed the precipitates to be amorphous, or possibly poorly crystalline, iron-rich minerals. Clone libraries developed from 16S rDNA sequences extracted from microbial mat communities associated with the precipitates revealed the presence of microorganisms related to the neutrophilic iron oxidizing bacteria Gallionella and Sideroxydans. Sequences from these libraries also indicated the presence of significant populations of organisms related to bacteria in the genera Aquaspirillum, Pseudomonas, Sphingomonas, and Nitrospira. These geosymbiotic systems appears to be significant not only for the biogeochemical cycling of iron in the creek, but also for the cycling of organic species, inorganic nutrients, and trace metals.

Keywords: Iron oxide; Biomineral; Siderophores; Organic acids; Neutrophilic iron oxidizing bacteria; Circumneutral iron oxidation』

1. Introduction
2. Materials and methods
 2.1. Site description and sampling procedure
 2.2. Inorganic aqueous chemistry
 2.3. Organic aqueous chemistry
 2.4. Geochemical modeling
 2.5. Characterization of sediments
 2.6. Optical microscopy
 2.7. Electron microscopy
 2.8. Microbial community analysis
3. Results and discussion
 3.1. Aqueous chemistry
 3.2. Organic species
 3.3. Microscopy of sediments and microbial mats
 3.4. Microbial ecology of creek microbial mats
 3.5. Microbial populations, iron oxidation, and siderophore production in sample 3BR
 3.6. Microbial populations, iron oxidation, and siderophore production in sample 3BH
4. Conclusions
Acknowledgements
Appendix A. Supplementary data
References


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