Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 12, issue 18
Biogeosciences, 12, 5277-5289, 2015
https://doi.org/10.5194/bg-12-5277-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 12, 5277-5289, 2015
https://doi.org/10.5194/bg-12-5277-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 16 Sep 2015

Research article | 16 Sep 2015

Iron encrustations on filamentous algae colonized by Gallionella-related bacteria in a metal-polluted freshwater stream

J. F. Mori1, T. R. Neu2, S. Lu1,3, M. Händel4, K. U. Totsche4, and K. Küsel1,3 J. F. Mori et al.
  • 1Institute of Ecology, Aquatic Geomicrobiology, Friedrich Schiller University Jena, Dornburger Strasse 159, 07743 Jena, Germany
  • 2Department of River Ecology, Helmholtz Centre for Environmental Research – UFZ, Brueckstrasse 3A, 39114 Magdeburg, Germany
  • 3German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Deutscher Platz 5e, 04103 Leipzig, Germany
  • 4Institute of Geosciences, Hydrogeology, Friedrich Schiller University Jena, Burgweg 11, 07749 Jena, Germany

Abstract. Filamentous macroscopic algae were observed in slightly acidic to circumneutral (pH 5.9–6.5), metal-rich stream water that leaked out from a former uranium mining district (Ronneburg, Germany). These algae differed in color and morphology and were encrusted with Fe-deposits. To elucidate their potential interaction with Fe(II)-oxidizing bacteria (FeOB), we collected algal samples at three time points during summer 2013 and studied the algae-bacteria-mineral compositions via confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectra, and a 16S and 18S rRNA gene-based bacterial and algae community analysis. Surprisingly, sequencing analysis of 18S rRNA gene regions of green and brown algae revealed high homologies with the freshwater algae Tribonema (99.9–100 %). CLSM imaging indicated a loss of active chloroplasts in the algae cells, which may be responsible for the change in color in . Fe(III)-precipitates on algal cells identified as ferrihydrite and schwertmannite by FTIR were associated with microbes and extracellular polymeric substances (EPS)-like glycoconjugates. SEM imaging revealed that while the green algae were fully encrusted with Fe-precipitates, the brown algae often exhibited discontinuous series of precipitates. This pattern was likely due to the intercalary growth of algal filaments which allowed them to avoid detrimental encrustation. 16S rRNA gene-targeted studies revealed that Gallionella-related FeOB dominated the bacterial RNA and DNA communities (70–97 and 63–96 %, respectively), suggesting their capacity to compete with the abiotic Fe-oxidation under the putative oxygen-saturated conditions that occur in association with photosynthetic algae. Quantitative PCR (polymerase chain reaction) revealed even higher Gallionella-related 16S rRNA gene copy numbers on the surface of green algae compared to the brown algae. The latter harbored a higher microbial diversity, including some putative predators of algae. A loss of chloroplasts in the brown algae could have led to lower photosynthetic activities and reduced EPS production, which is known to affect predator colonization. Collectively, our results suggest the coexistence of oxygen-generating algae Tribonema sp. and strictly microaerophilic neutrophilic FeOB in a heavy metal-rich environment.

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We studied filamentous macroscopic algae growing in metal-rich stream water that leaked from a former uranium-mining district. These algae were encrusted with Fe-deposits that were associated with microbes, mainly Gallionella-related Fe-oxidizing bacteria, and extracellular polymeric substances. Algae with a lower number of chloroplasts often exhibited discontinuous series of precipitates, likely due to the intercalary growth of algae which allowed them to avoid detrimental encrustation.
We studied filamentous macroscopic algae growing in metal-rich stream water that leaked from a...
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