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Title: Carbon dioxide fixation by Metallosphaera yellowstonensis and acidothermophilic iron-oxidizing microbial communities from Yellowstone National Park

The fixation of inorganic carbon (as carbon dioxide) has been documented in all three domains of life and results in the biosynthesis of a diverse suite of organic compounds that support the growth of heterotrophic organisms. The primary aim of this study was to assess the importance of carbon dioxide fixation in high-temperature Fe(III)-oxide mat communities and in pure cultures of one of the dominant Fe(II)-oxidizing organisms (Metallosphaera yellowstonensis strain MK1) present in situ. Protein-encoding genes of the complete 3-hydroxypropionate/4-hydroxybutyrate (3-HP/4-HB) carbon fixation pathway were identified in pure-cultures of M. yellowstonensis strain MK1. Metagenome sequencing from the same environments also revealed genes for the 3-HP/4-HB pathway belonging to M. yellowstonensis populations, as well as genes for a complete reductive TCA cycle from Hydrogenobaculum spp. (Aquificales). Stable isotope (13CO2) labeling was used to measure the fixation of CO2 by M. yellowstonensis strain MK1, and in ex situ assays containing live Fe(III)-oxide microbial mats. Results showed that M. yellowstonensis strain MK1 fixes CO2 via the 3-HP/4-HB pathway with a fractionation factor of ~ 2.5 ‰. Direct analysis of the 13C composition of dissolved inorganic C (DIC), dissolved organic C (DOC), landscape C and microbial mat C showed that mat C is comprisedmore » of both DIC and non-DIC sources. The estimated contribution of DIC carbon to biomass C (> ~ 35%) is reasonably consistent with the relative abundance of known chemolithoautotrophs and corresponding CO2 fixation pathways detected in metagenome sequence. The significance of DIC as a major source of carbon for Fe-oxide mat communities provides a foundation for examining microbial interactions in these systems that are dependent on the activity of autotrophic organisms such as Hydrogenobaculum and Metallosphaera spp.« less
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Journal Article
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Journal Name: Applied and Environmental Microbiology, 80(9):2665-2671
Research Org:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
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Country of Publication:
United States
Sulfolobales, Crenarchaeota, stable isotope analysis, thermophile, autotrophy