Isolation and Distribution of a Novel Iron-Oxidizing Crenarchaeon from Acidic Geothermal Springs in Yellowstone National Park

Abstract

Novel thermophilic crenarchaea have been observed in Fe(III) oxide microbial mats of Yellowstone National Park (YNP); however, no definitive work has identified specific microorganisms responsible for the oxidation of Fe(II). The objectives of the current study were to isolate and characterize an Fe(II)-oxidizing member of the Sulfolobales observed in previous 16S rRNA gene surveys and to determine the abundance and distribution of close relatives of this organism in acidic geothermal springs containing high concentrations of dissolved Fe(II). Here we report the isolation and characterization of the novel, Fe(II)-oxidizing, thermophilic, acidophilic organism Metallosphaera sp. strain MK1 obtained from a well-characterized acid-sulfate-chloride geothermal spring in Norris Geyser Basin, YNP. Full-length 16S rRNA gene sequence analysis revealed that strain MK1 exhibits only 94.9 to 96.1% sequence similarity to other known Metallosphaera spp. and less than 89.1% similarity to known Sulfolobus spp. Strain MK1 is a facultative chemolithoautotroph with an optimum pH range of 2.0 to 3.0 and an optimum temperature range of 65 to 75°C. Strain MK1 grows optimally on pyrite or Fe(II) sorbed onto ferrihydrite, exhibiting doubling times between 10 and 11 h under aerobic conditions (65°C). The distribution and relative abundance of MK1-like 16S rRNA gene sequences in 14 acidic geothermal springs containing Fe(III) oxide microbial mats were evaluated. Highly related MK1-like 16S rRNA gene sequences (>99% sequence similarity) were consistently observed in Fe(III) oxide mats at temperatures ranging from 55 to 80°C. Quantitative PCR using Metallosphaera-specific primers confirmed that organisms highly similar to strain MK1 comprised up to 40% of the total archaeal community at selected sites. The broad distribution of highly related MK1-like 16S rRNA gene sequences in acidic Fe(III) oxide microbial mats is consistent with the observed characteristics and growth optima of Metallosphaera-like strain MK1 and emphasizes the importance of this newly described taxon in Fe(II) chemolithotrophy in acidic high-temperature environments of YNP.

Hydrogen Peroxide Cycling in High-Temperature Acidic Geothermal Springs and Potential Implications for Oxidative Stress Response

“…Increases in O 2 during the day may in part be responsible for increases in microbial growth of M. yellowstonensis and Hydrogenobaculum, which are both aerobic (Kozubal et al, 2008;Takacs-Vesbach et al, 2013;Jennings et al, 2014). Higher 16S rRNA gene expression levels of Metallosphaera compared to Hydrogenobaculum in both environments ( Figure 5) were consistent with higher relative abundances of Metallosphaera observed previously in the upper ∼1 mm of mature Fe(III)-oxide mats, which also corresponds to the active O 2 -consuming layer (Beam et al, 2016).…”

“…The rod-shaped bacteria Hydrogenobaculum spp. initiate biofilm attachment, and the iron-oxidizing archaea Metallosphaera yellowstonensis (strain MK1) are responsible for the oxidation of Fe(II) and subsequent accretion of Fe(III)-oxides (Macur et al, 2004;Kozubal et al, 2008;Takacs-Vesbach et al, 2013;Jennings et al, 2014;Beam et al, 2016). Oxygen is a key driver of microbial growth and subsequent mat morphology (Kempes et al, 2014), and its diffusion into the mat is the rate-limiting factor for Fe(III)-oxide mat formation (Beam et al, 2016).…”

Geoarchaeota: a new candidate phylum in the Archaea from high-temperature acidic iron mats in Yellowstone National Park

“…(10-15%) as determined by three separate phylogenetic methods. All three of these organisms are B1 mm diameter cocci (Boyd et al, 2007;Kozubal et al, 2008;this study). Most of the remaining sequences belong to Vulcanisaeta-or Hydrogenobaculum-like spp.…”

“…Previous studies of acidic ferric iron mats, in particular, have shown a remarkable diversity of archaea, which corresponds with the combination of unique geochemistry and high temperature of these systems (Inskeep et al, 2005;Kozubal et al, 2008;Inskeep et al, 2010;Kozubal et al, 2012). Prior 16S rRNA gene sequencing of high-temperature (65-80 1C) acidic Fe-oxide mats has revealed the presence of novel archaea, but cultivation of representative(s) from this group has yet to be successful.…”

Microbes: Mini Iron Factories

“…Keywords Microbes Á Biomineralization Á Banded iron formation Á Geomicrobiology Earth has been a habitat for microbes almost since the beginning of its history and these microorganisms have flourished in extreme habitats such as Antartica, acid mine drainage, glacier ice, geothermal springs, and deep-sea vents [1][2][3][4][5][6][7]. Although not emphasized much but microbes play an important role in a number of geologic processes including weathering, diagenesis, biomobilization, bioimmobilization, biogeochemical cycle, mineral formations, transformations and biodegradation [8][9][10][11][12][13].…”