Browsing by Author "Whitmore, Laura M."

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Autotrophic Carbon Fixation in Crenarchaeota from Yellowstone National Park
(2013-03) Whitmore, Laura M.; Inskeep, William
Autotrophy in the archaea has recently been described as an important and under-studied source of global carbon fixation. Several archaeal species are found in ferric oxyhydroxide mats from acidic geothermal springs in Yellowstone National Park. The springs are an exceptional natural laboratory for studying microorganisms in constrained systems. However, primary productivity had not been demonstrated in these systems. The goal of this study was to confirm autotrophic growth in pure Metallosphaera yellowstonensis, a dominant community member in Fe(III)-oxide mats, and relate this to in situ microbial communities. M. yellowstonensis was grown chemolithoautotrophically with pyrite as the electron donor, oxygen as the electron acceptor, and 13CO2 as the sole carbon source. At post log-phase, biomass was analyzed using isotope-ratio mass spectrometry (IRMS) at Pacific Northwest National Laboratory. The results demonstrated that M. yellowstonensis is capable of inorganic carbon fixation. Furthermore, the isotope fractionation value was consistent with an operating 3-hydroxypropionate/4-hydroxybutyrate cycle, characteristic in other Sulfolobales. Ex situ Fe(III)-oxide mat samples were incubated with pyrite, oxygen, and 13CO2, and analyzed by IRMS. The data show that under limited organic carbon, these communities are capable of CO2 fixation. Currently, transcriptomics and q-rt-PCR are being utilized to confirm the expression of key autotrophy genes.
Formaldehyde as a carbon and electron shuttle between autotroph and heterotroph populations in acidic hydrothermal vents of Norris Geyser Basin, Yellowstone National Park
(2016-05) Moran, James J.; Whitmore, Laura M.; Isern, Nancy G.; Romine, Margaret F.; Riha, Krystin M.; Inskeep, William P.; Kreuzer, Helen W.
The Norris Geyser Basin in Yellowstone National Park contains a large number of hydrothermal systems, which host microbial populations supported by primary productivity associated with a suite of chemolithotrophic metabolisms. We demonstrate that Metallosphaera yellowstonensis MK1, a facultative autotrophic archaeon isolated from a hyperthermal acidic hydrous ferric oxide (HFO) spring in Norris Geyser Basin, excretes formaldehyde during autotrophic growth. To determine the fate of formaldehyde in this low organic carbon environment, we incubated native microbial mat (containing M. yellowstonensis) from a HFO spring with 13C-formaldehyde. Isotopic analysis of incubation-derived CO2 and biomass showed that formaldehyde was both oxidized and assimilated by members of the community. Autotrophy, formaldehyde oxidation, and formaldehyde assimilation displayed different sensitivities to chemical inhibitors, suggesting that distinct sub-populations in the mat selectively perform these functions. Our results demonstrate that electrons originally resulting from iron oxidation can energetically fuel autotrophic carbon fixation and associated formaldehyde excretion, and that formaldehyde is both oxidized and assimilated by different organisms within the native microbial community. Thus, formaldehyde can effectively act as a carbon and electron shuttle connecting the autotrophic, iron oxidizing members with associated heterotrophic members in the HFO community.
Integration of metagenomic and stable carbon isotope evidence reveals the extent and mechanisms of carbon dioxide fixation in high-temperature microbial communities.
(2017-02) Jennings, Ryan deM.; Moran, James J.; Jay, Zackary J.; Beam, Jacob P.; Whitmore, Laura M.; Kozubal, Mark A.; Kreuzer, Helen W.; Inskeep, William P.
Although the biological fixation of CO2 by chemolithoautotrophs provides a diverse suite of organic compounds utilized by chemoorganoheterotrophs as a carbon and energy source, the relative amounts of autotrophic C in chemotrophic microbial communities are not well-established. The extent and mechanisms of CO2 fixation were evaluated across a comprehensive set of high-temperature, chemotrophic microbial communities in Yellowstone National Park by combining metagenomic and stable 13C isotope analyses. Fifteen geothermal sites representing three distinct habitat types (iron-oxide mats, anoxic sulfur sediments, and filamentous “streamer” communities) were investigated. Genes of the 3-hydroxypropionate/4-hydroxybutyrate, dicarboxylate/4-hydroxybutyrate, and reverse tricarboxylic acid CO2 fixation pathways were identified in assembled genome sequence corresponding to the predominant Crenarchaeota and Aquificales observed across this habitat range. Stable 13C analyses of dissolved inorganic and organic C (DIC, DOC), and possible landscape C sources were used to interpret the 13C content of microbial community samples. Isotope mixing models showed that the minimum fractions of autotrophic C in microbial biomass were >50% in the majority of communities analyzed. The significance of CO2 as a C source in these communities provides a foundation for understanding community assembly and succession, and metabolic linkages among early-branching thermophilic autotrophs and heterotrophs.