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Applied and Environmental Microbiology, April 2004, p. 2119-2128, Vol. 70, No. 4
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.4.2119-2128.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Determination of Nitrogen-Fixing Phylotypes in Lyngbya sp. and Microcoleus chthonoplastes Cyanobacterial Mats from Guerrero Negro, Baja California, Mexico

Enoma O. Omoregie,1 Lori L. Crumbliss,1 Brad M. Bebout,2 and Jonathan P. Zehr1*

Department of Ocean Sciences and Institute of Marine Sciences, University of California, Santa Cruz, California 95064,1 Exobiology Branch, NASA Ames Research Center, Moffett Field, California 940352

Received 25 August 2003/ Accepted 1 December 2003

In many environments, biological nitrogen fixation can alleviate nitrogen limitation. The high rates of N2 fixation often observed in cyanobacterial mats suggest that N2 fixation may be an important source of N. In this study, organisms expressing nifH were identified in a Lyngbya sp.- and two Microcoleus chthonoplastes-dominated cyanobacterial mats. The pattern of nitrogenase activity was determined for the Lyngbya sp. mat and a Microcoleus chthonoplastes mat sampled directly in Guerrero Negro, Mexico. Their maximum rates were 23 and 15 µmol of C2H4 m–2 h–1, respectively. The second Microcoleus mat, which was maintained in a greenhouse facility, had a maximum rate of 40 µmol of C2H4 m–2 h–1. The overall diel pattern of nitrogenase activity in the three mats was similar, with the highest rates of activity occurring during the dark period. Analysis of nifH transcripts by reverse transcription-PCR revealed that several different organisms were expressing nifH during the dark period. nifH phylotypes recovered from these mats were similar to sequences from the unicellular cyanobacterial genera Halothece, Myxosarcina, and Synechocystis, the filamentous cyanobacterial genera Plectonema and Phormidium, and several bacterial nifH groups. The results of this study indicate that several different organisms, some of which were not previously known to fix nitrogen, are likely to be responsible for the observed dark-period nitrogenase activity in these cyanobacterial mats.

* Corresponding author. Mailing address: Department of Ocean Sciences and Institute of Marine Sciences, Earth and Marine Science Bldg., University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064. Phone: (831) 459-4009. Fax: (831) 459-4882. E-mail: zehrj{at}ucsc.edu.

Applied and Environmental Microbiology, April 2004, p. 2119-2128, Vol. 70, No. 4
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.4.2119-2128.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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