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Applied and Environmental Microbiology, December 2004, p. 7070-7077, Vol. 70, No. 12
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.12.7070-7077.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Bacterial Life and Dinitrogen Fixation at a Gypsum Rock

Gudrun Boison,{dagger} Alexander Mergel, Helena Jolkver, and Hermann Bothe*

Botanical Institute, The University of Cologne, Cologne, Germany

Received 23 March 2004/ Accepted 26 July 2004

The organisms of a bluish-green layer beneath the shards of a gypsum rock were characterized by molecular techniques. The cyanobacterial consortium consisted almost exclusively of Chroococcidiopsis spp. The organisms of the shards expressed nitrogenase activity (C2H2 reduction) aerobically and in light. After a prolonged period of drought at the rock, the cells were inactive, but they resumed nitrogenase activity 2 to 3 days after the addition of water. In a suspension culture of Chroococcidiopsis sp. strain PCC7203, C2H2 reduction required microaerobic conditions and was strictly dependent on low light intensities. Sequencing of a segment of the nitrogenase reductase gene (nifH) indicated that Chroococcidiopsis possesses the alternative molybdenum nitrogenase 2, expressed in Anabaena variabilis only under reduced O2 tensions, rather than the widespread, common molybdenum nitrogenase. The shards apparently provide microsites with reduced light intensities and reduced O2 tension that allow N2 fixation to proceed in the unicellular Chroococcidiopsis at the gypsum rock, unless the activity is due to minute amounts of other, very active cyanobacteria. Phylogenetic analysis of nifH sequences tends to suggest that molybdenum nitrogenase 2 is characteristic of those unicellular or filamentous, nonheterocystous cyanobacteria fixing N2 under microaerobic conditions only.

* Corresponding author. Mailing address: Botanical Institute, The University of Cologne, Gyrhofstr. 15, D-50923 Cologne, Germany. Phone: 49 221 470 2760. Fax: 49 221 470 5039. E-mail: Hermann.Bothe{at}uni-koeln.de.

{dagger} Present address: NIOO—Centre for Estuarine and Coastal Ecology, Yerseke, The Netherlands.

Applied and Environmental Microbiology, December 2004, p. 7070-7077, Vol. 70, No. 12
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.12.7070-7077.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.





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