鉄含有温泉に生息するシアノバクテリアの鉄毒性に対する耐性

Microbial metabolism in iron-rich hot springs can provide insights into the role of both ancient and contemporary microbes related to iron oxidation. The oxidation of Fe(II) in some ancient periods, resulting in iron deposition, can partially be understood from the reaction with oxygen produced by cyanobacteria or oxygenic phototrophs. However, Fe(II) together with oxygen is toxic to many organisms, and cyanobacteria are no exception. A previous study showed that cyanobacteria responded negatively to anoxic and Fe(II) rich conditions. In this study, cyanobacteria obtained from iron-rich environments were tested to determine whether they were tolerant to iron-rich conditions. Two types of enrichment culture were obtained from microbial mats in Jinata hot springs in Shikine island, one of Izu islands. The marine hot springs had neutral pH and included 250 μM Fe(II). One area contained unicellular cyanobacteria (JNT 01) and phylogenetic analysis indicated that the bacterium is related to Cyanobacterium aponium (99 % identity). Cyanobacteria from the springs were cultured in the absence of Fe(II), aerobically. Then, the cyanobacteria cultured were grown in air-tight bottles under anoxic and Fe(II) containing conditions, at the beginning, in order to reveal the effect of Fe(II) on growth. The growth of one microcosm, containing a morphotype referred to here as JNT 01, was different from Synechococcus PCC 7002, as a control. JNT 01 in 600 μM initial Fe(II) grew as fast as in 0 μM Fe(II). The growth of Synechococcus PCC 7002 in 600 μM Fe(II) was about half of the growth in 0 μM Fe(II). During the growth of cells, the Fe(II) concentration diminished in several hours in both cultures. To reveal the difference in the growth of JNT 01 and Synechococcus PCC 7002 with Fe(II) in early growth phase, the growth conditions were changed. Synechococcus PCC 7002 sometimes grew in 200 μM better than in 0 μM. It seems to be the effect of Fe on the metabolism. Therefore, the timing of the addition of ferric citrate – a growth nutrient – was changed from before autoclaving to after autoclaving. Under the changed conditions, the growth of JNT 01 and Synechococcus PCC 7002 was similar. These experiments seemed to suggest that Synechococcus PCC 7002, but not JNT 01, was sensitive to an effect of the form of Fe as a nutrient for growth, and that the timing of autoclaving affected this. Since Fe(II) decreased in less than 24 hours in these experiments, it was difficult to make conclusions about the effects of Fe(II). To investigate these effects on growing cells, the initial growth of cells was examined. Less than 24 hours after the start of growth, Fe(II) was decreasing but still present. During this period, the growth of JNT 01 is significantly different from the growth of PCC 7002. In the later time when Fe(II) decreased, the difference became less significant. These results together suggested that the enriched unicellular cyanobacteria inhabiting in the Fe(II)-rich hot springs were tolerant to the ferrous iron rich conditions. It is possible that they have been adapted to iron-rich environments which are similar to that expected for Precambrian environments. This study provides insights into ancient iron transformations and mechanisms of Fe(II) toxicity in both modern and ancient ocean cyanobacteria.首都大学東京, 2018-03-25, 修士（理学）首都大学東

Geochemical and metagenomic characterization of Jinata Onsen, a Proterozoic-analog hot spring, reveals novel microbial diversity including iron-tolerant phototrophs and thermophilic lithotrophs

Hydrothermal systems, including terrestrial hot springs, contain diverse geochemical conditions that vary over short spatial scales due to progressive interactions between reducing hydrothermal fluids, the oxygenated atmosphere, and, in some cases, seawater. At Jinata Onsen on Shikinejima Island, Japan, an intertidal, anoxic, iron-rich hot spring mixes with the oxygenated atmosphere and seawater over short spatial scales, creating diverse chemical potentials and redox pairs over a distance of ~10 m. We characterized geochemical conditions along the outflow of Jinata Onsen as well as the microbial communities present in biofilms, mats, and mineral crusts along its traverse using 16S rRNA gene amplicon and genome-resolved shotgun metagenomic sequencing. Microbial communities significantly changed downstream as temperatures and dissolved iron concentrations decreased and dissolved oxygen increased. Biomass was more limited near the spring source than downstream, and primary productivity appeared to be fueled by the oxidation of ferrous iron and molecular hydrogen by members of Zetaproteobacteria and Aquificae. The microbial community downstream was dominated by oxygenic Cyanobacteria. Cyanobacteria are abundant and active even at ferrous iron concentrations of ~150 μM, which challenges the idea that iron toxicity limited cyanobacterial expansion in Precambrian oceans. Several novel lineages of Bacteria are also present at Jinata Onsen, including previously uncharacterized members of the phyla Chloroflexi and Calditrichaeota, positioning Jinata Onsen as a valuable site for the future characterization of these clades

Thermophilic Lithotrophy and Phototrophy in an Intertidal, Iron-rich, Geothermal Spring

Hydrothermal systems, including terrestrial hot springs, contain diverse and systematic arrays of geochemical conditions that vary over short spatial scales due to progressive interaction between the reducing hydrothermal fluids, the oxygenated atmosphere, and in some cases seawater. At Jinata Onsen, on Shikinejima Island, Japan, an intertidal, anoxic, iron- and hydrogen-rich hot spring mixes with the oxygenated atmosphere and sulfate-rich seawater over short spatial scales, creating an enormous range of redox environments over a distance ~10 m. We characterized the geochemical conditions along the outflow of Jinata Onsen as well as the microbial communities present in biofilms, mats, and mineral crusts along its traverse via 16S amplicon and shotgun metagenomic sequencing. The microbial community changed significantly downstream as temperatures and dissolved iron concentrations dropped and dissolved oxygen rose. Near the spring source, primary productivity appears limited, and is fueled primarily by oxidation of ferrous iron and molecular hydrogen by members of the Zetaproteobacteria and Aquificae, while downstream the microbial community is dominated by oxygenic Cyanobacteria. At Jinata Onsen, Cyanobacteria are abundant and productive even at ferrous iron concentrations of ~150 μM, which challenges the idea that iron toxicity limited cyanobacterial expansion in the Precambrian oceans. Several novel lineages of Bacteria are also present at Jinata Onsen, including previously uncharacterized members of the Chloroflexi and Caldithrichaeota phyla, positioning Jinata Onsen as a valuable site for future characterization of these clades