Linking geochemical processes with microbial community analysis: successional dynamics in an arsenic-rich, acid-sulphate-chloride geothermal spring

摘要

The source waters of acid-sulphate-chloride (ASC) geothermal springs located in Morris Geyser Basin, Yellowstone National Park contain several reduced chemical species, including H_2, H_2S, As(lll), and Fe(ll), which may serve as electron donors driving chemolithotrophic metabolism. Microorganisms thriving in these environments must also cope with high temperatures, low pH (-3), and high concentrations of sulphide, As(lll), and boron. The goal of the current study was to correlate the temporal andspatial distribution of bacterial and archaeal populations with changes in temperature and geochemical energy gradients occurring throughout a newly formed (redirected) outflow channel of an ASC spring. A suite of complimentary analyses including aqueousgeochemistry, microscopy, solid phase identification, and 16S rDNA sequence distribution were used to correlate the appearance of specific microbial populations with biogeochemical processes mediating S, Fe, and As cycling and subsequent biomineralizationof As(V)-rich hydrous ferric oxide (HFO) mats. Rapid As(lll) oxidation (maximum first order rate constants ranged from 4 to 5 min~(-1), t_(1/2) = 0.17 - 0.14 min) was correlated with the appearance of Hydrogenobaculum and Tft/omonas-like populations, whereas the biogenesis of As(V)-rich HFO microbial mats (mole ratios of As:Fe -0.7) was correlated with the appearance of Metallosphaera, Addimicrobium, and Thiomonas-like populations. Several 165 sequences detected near the source were closely related tosequences of chemolithotrophic hyperthermophilic populations including Stygiolobus and Hydrogenobaculum organisms that are known H_ 2oxidizers. The use of H_2, reduced S(-ll,0), Fe(ll) and perhaps As(lll) by different organisms represented throughout theoutflow channel was supported by thermodynamic calculations, confirming highly exergonic redox couples with these electron donors. Results from this work demonstrated that chemical energy gradients play an important role in establishing distinct community structure as a function of distance from geothermal spring discharge.