Effect of salinity on nitrogenase activity and composition of the active diazotrophic community in intertidal microbial
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ORIGINAL PAPER
Effect of salinity on nitrogenase activity and composition of the active diazotrophic community in intertidal microbial mats Ina Severin • Veronique Confurius-Guns Lucas J. Stal
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Received: 7 June 2011 / Revised: 9 December 2011 / Accepted: 16 December 2011 / Published online: 8 January 2012 Ó The Author(s) 2012. This article is published with open access at Springerlink.com
Abstract Microbial mats are often found in intertidal areas experiencing a large range of salinities. This study investigated the effect of changing salinities on nitrogenase activity and on the composition of the active diazotrophic community (nifH transcript libraries) of three types of microbial mats situated along a littoral gradient. All three mat types exhibited highest nitrogenase activity at salinities close to ambient seawater or lower. The response to lower or higher salinity was strongest in mats higher up in the littoral zone. Changes in nitrogenase activity as the result of exposure to different salinities were accompanied by changes in the active diazotrophic community. The two stations higher up in the littoral zone showed nifH expression by Cyanobacteria (Oscillatoriales and Chroococcales) and Proteobacteria (Gammaproteobacteria and Deltaproteobacteria). At these
stations, a decrease in the relative contribution of Cyanobacteria to the nifH transcript libraries was observed at increasing salinity coinciding with a decrease in nitrogenase activity. The station at the low water mark showed low cyanobacterial contribution to nifH transcript libraries at all salinities but an increase in deltaproteobacterial nifH transcripts under hypersaline conditions. In conclusion, increased salinities caused decreased nitrogenase activity and were accompanied by a lower proportion of cyanobacterial nifH transcripts. Keywords Salinity Microbial mat Nitrogen fixation Cyanobacteria Proteobacteria
Introduction Communicated by Joerg Overmann.
Electronic supplementary material The online version of this article (doi:10.1007/s00203-011-0787-5) contains supplementary material, which is available to authorized users. I. Severin V. Confurius-Guns L. J. Stal (&) Department of Marine Microbiology, Royal Netherlands Institute of Sea Research (NIOZ), PO Box 140, 4400 AC Yerseke, The Netherlands e-mail: [email protected] I. Severin e-mail: [email protected] Present Address: I. Severin Department of Ecology and Genetics/Limnology, Evolutionary Biology Centre, Uppsala University, 75236 Uppsala, Sweden L. J. Stal Department of Aquatic Microbiology, Institute of Biodiversity and Ecosystem Dynamics, University of Amsterdam, PO Box 94248, 1090 GE Amsterdam, The Netherlands
Coastal ecosystems, including salt marshes, mangroves, wetlands, estuaries and bays, are often characterized by highly fluctuating environmental conditions, mainly due to the tidal cycle. One important factor in intertidal areas is salinity. Salinities range from almost freshwater, for example, through runoff or upwelling groundwater, to hypersaline conditio
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