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Halotaxis of cyanobacteria in an intertidal hypersaline microbial mat

Authors

  • Katharina Kohls,

    Corresponding author
    1. Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, 28359 Bremen, Germany.
      *E-mail kkohls@mpi-bremen.de; Tel. (+49) 421 2028608; Fax (+49) 421 2028690.
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  • Raeid M. M. Abed,

    1. Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, 28359 Bremen, Germany.
    2. Sultan Qaboos University, College of Science- Biology Department, Al Khoud, Muscat, Sultanate of Oman.
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  • Lubos Polerecky,

    1. Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, 28359 Bremen, Germany.
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  • Miriam Weber,

    1. Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, 28359 Bremen, Germany.
    2. HYDRA Institute for Marine Sciences, Elba Field Station, Via del Forno 80, 57034 Campo nell'Elba (LI), Italy.
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  • Dirk De Beer

    1. Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, 28359 Bremen, Germany.
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*E-mail kkohls@mpi-bremen.de; Tel. (+49) 421 2028608; Fax (+49) 421 2028690.

Summary

An intertidal hypersaline cyanobacterial mat from Abu Dhabi (United Arab Emirates) exhibited a reversible change in its surface colour within several hours upon changes in salinity of the overlying water. The mat surface was orange-reddish at salinities above 15% and turned dark green at lower salinities. We investigated this phenomenon using a polyphasic approach that included denaturing gradient gel electrophoresis, microscopy, high-performance liquid chromatography, hyperspectral imaging, absorption spectroscopy, oxygen microsensor measurements and modelling of salinity dynamics. Filaments of Microcoleus chthonoplastes, identified based on 16S rRNA sequencing and morphology, were found to migrate up and down when salinity was decreased below or increased above 15%, respectively, causing the colour change of the mat uppermost layer. Migration occurred in light and in the dark, and could be induced by different salts, not only NaCl. The influence of salinity-dependent and independent physico-chemical parameters, such as water activity, oxygen solubility, H2S, gravity and light, was excluded, indicating that the observed migration was due to a direct response to salt stress. We propose to term this salinity-driven cyanobacterial migration as ‘halotaxis’, a process that might play a vital role in the survival of cyanobacteria in environments exposed to continuous salinity fluctuations such as intertidal flats.

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