Abstract
The microbial community composition and its functionality was assessed for hydrothermal fluids and volcanic ash sediments from Haungaroa and hydrothermal fluids from the Brothers volcano in the Kermadec island arc (New Zealand). The Haungaroa volcanic ash sediments were dominated by epsilonproteobacterial Sulfurovum sp. Ratios of electron donor consumption to CO2 fixation from respective sediment incubations indicated that sulfide oxidation appeared to fuel autotrophic CO2 fixation, coinciding with thermodynamic estimates predicting sulfide oxidation as the major energy source in the environment. Transcript analyses with the sulfide-supplemented sediment slurries demonstrated that Sulfurovum prevailed in the experiments as well. Hence, our sediment incubations appeared to simulate environmental conditions well suggesting that sulfide oxidation catalyzed by Sulfurovum members drive biomass synthesis in the volcanic ash sediments. For the Haungaroa fluids no inorganic electron donor and responsible microorganisms could be identified that clearly stimulated autotrophic CO2 fixation. In the Brothers hydrothermal fluids Sulfurimonas (49%) and Hydrogenovibrio/Thiomicrospira (15%) species prevailed. Respective fluid incubations exhibited highest autotrophic CO2 fixation if supplemented with iron(II) or hydrogen. Likewise catabolic energy calculations predicted primarily iron(II) but also hydrogen oxidation as major energy sources in the natural fluids. According to transcript analyses with material from the incubation experiments Thiomicrospira/Hydrogenovibrio species dominated, outcompeting Sulfurimonas. Given that experimental conditions likely only simulated environmental conditions that cause Thiomicrospira/Hydrogenovibrio but not Sulfurimonas to thrive, it remains unclear which environmental parameters determine Sulfurimonas’ dominance in the Brothers natural hydrothermal fluids.
Highlights
Hydrothermal fluids emitted from cracks and fissures of the seafloor transport numerous reduced chemical compounds to the surface
Incubation experiments with fluid and tephra samples were conducted to identify whether hydrogen, iron(II) or sulfide primarily fuel autotrophic CO2 fixation in these habitat types
Since no geochemical data is available for porewater of these fluids we refer to hydrothermal emissions nearby to disclose general trends in chemical compositions
Summary
Hydrothermal fluids emitted from cracks and fissures of the seafloor transport numerous reduced chemical compounds to the surface. We compare the microbial community compositions and their functionality in two hydrothermal fluid and one tephra (volcanic ash sediment) samples from two locations along the Kermadec island arc system. For this purpose, incubation experiments were set up, consumption of amended inorganic electron donor and autotrophic CO2 fixation was measured. The phylogenetic diversity of the transcriptomes for each type of incubation experiment was compared with each other and with the initial starting community composition
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