2 items with the tag “reduction

  • Project 1E: Microbial Communities in Chocolate Pots Hot Spring, Yellowstone National Park
    NAI 2014 University of Wisconsin Annual Report

    DNA was extracted from samples obtained from cores collected at six locations along a transect following the main fluid flow path at at Chocolate Pots (CP) hot spring, Yellowstone National Park. 454 pyrosequencing of 16S rRNA gene amplicons was performed on the extracts, resulting in the generation more than 70 amplicon libraries, each containing a between ca. 2500 and 7500 ca. 300 base pair-long reads. The raw reads were processed and analyzed for their phylogenetic affiliation and other comparisons using the QIIME pipeline. The results indicate that microbial communities in the upper few cm of the Fe/Si-rich CP deposits varied significantly along the sampling transect. Communities at two sites most proximal to the vent source differed substantially from one another and from communities at downstream sites. Although communities at downstream sites were not identical, they were more similar to one another than to the vent-proximal sites. A wide diversity of prokaryotic taxa, including both Bacteria and Archaea, were identified in the libraries, many of which are only distantly (e.g. <90% similarity in 16S rRNA gene sequence) related to known taxa. Communities in cores close to the vent were dominated by anaerobic taxa, many of which have the potential to function as Fe(III) reducers. This result is consistent with the relatively high abundance of reduced (ferrous) iron [Fe(II)] and the rapid rate of Fe(II) production observed in in vitro Fe(III) reduction experiments with material from sites near the vent. Abundant taxa at downstream sites included organisms related to the known Fe(II)-oxidizing organism Sideroxydans paludicola. These results are consistent with Fe geochemical data, which indicate that Fe(II) oxidation is likely the dominant Fe redox cycling pathway in deposits more than 1-2 meters from the vent source. A detailed metagenomic analysis of communities in the upper 1 cm at three sites is underway, with the goal of confirming the function of recognized taxa, and revealing the identity and function of potentially novel Fe redox cycling taxa.

    ROADMAP OBJECTIVES: 2.1 4.1 5.1 5.3 7.1
  • Project 1D: Iron Biogeochemistry in Chocolate Pots Hot Spring, Yellowstone National Park
    NAI 2014 University of Wisconsin Annual Report

    Small cores were collected from six locations along a transect following the main fluid flow path at Chocolate Pots (CP) hot spring, Yellowstone National Park. The cores were sectioned at 1 cm intervals, and the solids subjected to sequential extraction to isolate different Fe pools. The results showed that cores proximal to the vent outlet contained significant quantities of dissolved/colloidal and HCl-extractable reduced (ferrous) iron [Fe(II)]. Fe recovered from the other cores was present entirely as Fe(III). The most likely explanation for these observations is that internal generation of Fe(II) via microbial reduction is taking place in deposits proximal to the vent. This interpretation is consistent with rapid Fe(II) production during anaerobic incubation of near-vent deposits. Our results provide direct evidence of Fe(III) oxide reduction in deposits proximal to the main vent at CP, and to our knowledge represent the first demonstration of in situ Fe(III) reduction in a circumneutral-pH geothermal environment analogous to those which may have been present on the ancient Earth and Mars. Preliminary stable Fe isotope measurements on the dissolved/colloidal and 0.5M HCl-extractable Fe fractions in the CP cores suggests that Fe(III) reduction influences the isotopic composition of Fe phases proximal to the vent. A comprehensive analysis of all Fe phases in the cores is underway and will be used to develop conceptual models of controls on the stable Fe isotope composition preserved in the hot spring deposits.

    ROADMAP OBJECTIVES: 2.1 4.1 5.3 7.1