Anammox bacterial populations in deep marine hypersaline gradient systems
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To extend the knowledge of anaerobic ammonium oxidation (anammox) habitats, bacterial communities were examined in two hypersaline sulphidic basins in Eastern Mediterranean Sea. The 2 m thick seawater–brine haloclines of the deep anoxic hypersaline basins Bannock and L’Atalante were sampled in intervals of 10 cm with increasing salinity. 15N isotope pairing incubation experiments showed the production of 29N2 and 30N2 gases in the chemoclines, ranging from 6.0 to 9.2 % salinity of the L’Atalante basin. Potential anammox rates ranged from 2.52 to 49.65 nmol N2 L−1 day−1 while denitrification was a major N2 production pathway, accounting for more than 85.5 % of total N2 production. Anammox-related 16S rRNA genes were detected along the L’Atalante and Bannock haloclines up to 24 % salinity, and the amplification of the hydrazine synthase genes (hzsA) further confirmed the presence of anammox bacteria in Bannock. Fluorescence in situ hybridisation and sequence analysis of 16S rRNA genes identified representatives of the marine anammox genus ‘Candidatus Scalindua’ and putatively new operational taxonomic units closely affiliated to sequences retrieved in marine environments that have documented anammox activity. ‘Scalindua brodae’ like sequences constituted up to 84.4 % of the sequences retrieved from Bannock. The anammox community in L’Atalante was different than in Bannock and was stratified according to salinity increase. This study putatively extends anammox bacterial habitats to extremely saline sulphidic ecosystems.
KeywordsAnaerobic ammonium oxidation Chemocline Hypersaline basins biodiversity Anammox activity 16S rRNA gene library
We thank the masters and crews of the R/V Urania, R/V Pelagia, R/V Universitatis for excellent technical assistance. K. Bakker is acknowledged for chemical analyses on board and at NIOZ (Texel, The Netherlands). Financial support was obtained from NWO projects MOCCHA and MIDDLE. Song and Tobias were supported by NSF (Biological Oceanography, grant OCE-0851435), Jetten by ERC (grant ERC232937), Rolli and Mapelli were supported by Università degli Studi di Milano, European Social Found (FSE) and Regione Lombardia (contract “Dote Ricerca”). This work has been conducted in the frame of the European Community FP7-KBBE-2010-4 project ULIXES, grant agreement N. 266473.
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