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Applied and Environmental Microbiology, November 2007, p. 7013-7022, Vol. 73, No. 21
0099-2240/07/$08.00+0     doi:10.1128/AEM.00548-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Physiological Adaptation of a Nitrate-Storing Beggiatoa sp. to Diel Cycling in a Phototrophic Hypersaline Mat{triangledown}

Susanne Hinck,1* Thomas R. Neu,2 Gaute Lavik,1 Marc Mussmann,3 Dirk de Beer,1 and Henk M. Jonkers1,4

Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, D-28359 Bremen, Germany,1 Helmholtz Centre for Environmental Research-UFZ, Brückstrasse 3a, D-39144 Magdeburg, Germany,2 University of Vienna, Ecology Centre, Faculty of Life Sciences, Althanstrasse 14, A-1090 Wien, Austria,3 Delft University of Technology, CITG, Microlab, P.O. Box 5048, NL-2600 GA Delft, The Netherlands4

Received 9 March 2007/ Accepted 23 August 2007

The aim of this study was to investigate the supposed vertical diel migration and the accompanying physiology of Beggiatoa bacteria from hypersaline microbial mats. We combined microsensor, stable-isotope, and molecular techniques to clarify the phylogeny and physiology of the most dominant species inhabiting mats of the natural hypersaline Lake Chiprana, Spain. The most dominant morphotype had a filament diameter of 6 to 8 µm and a length varying from 1 to >10 mm. Phylogenetic analysis by 16S rRNA gene comparison revealed that this type appeared to be most closely related (91% sequence identity) to the narrow (4-µm diameter) nonvacuolated marine strain MS-81-6. Stable-isotope analysis showed that the Lake Chiprana species could store nitrate intracellularly to 40 mM. The presence of large intracellular vacuoles was confirmed by fluorescein isothiocyanate staining and subsequent confocal microscopy. In illuminated mats, their highest abundance was found at a depth of 8 mm, where oxygen and sulfide co-occurred. However, in the dark, the highest Beggiatoa densities occurred at 7 mm, and the whole population was present in the anoxic zone of the mat. Our findings suggest that hypersaline Beggiatoa bacteria oxidize sulfide with oxygen under light conditions and with internally stored nitrate under dark conditions. It was concluded that nitrate storage by Beggiatoa is an optimal strategy to both occupy the suboxic zones in sulfidic sediments and survive the dark periods in phototrophic mats.

* Corresponding author. Mailing address: Max Planck Institute for Marine Microbiology, Celsiusstr. 1, D-28359 Bremen, Germany. Phone: 49-421-2028-843. Fax: 49-421-2028-690. E-mail: shinck{at}mpi-bremen.de

{triangledown} Published ahead of print on 31 August 2007.

Applied and Environmental Microbiology, November 2007, p. 7013-7022, Vol. 73, No. 21
0099-2240/07/$08.00+0     doi:10.1128/AEM.00548-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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