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Front. Microbiol. | doi: 10.3389/fmicb.2018.00356

Comparative genomics of the Baltic Sea toxic cyanobacteria Nodularia spumigena UHCC 0039 and its response to varying salinity

  • 1Department of Food and Environmental Sciences, University of Helsinki, Finland
  • 2Genetics & Experimental Bioinformatics, Spemann Graduate School of Biology and Medicine, University of Freiburg, Germany

Abstract
Salinity is an important abiotic factor controlling the distribution and abundance of Nodularia spumigena, the dominating diazotrophic and toxic phototroph, in the brackish water cyanobacterial blooms of the Baltic Sea. To expand the available genomic information for brackish water cyanobacteria, we sequenced the isolate Nodularia spumigena UHCC 0039 using an Illumina-SMRT hybrid sequencing approach, revealing a chromosome of 5 294 286 base pairs (bp) and a single plasmid of 92 326 bp. Comparative genomics in Nostocales showed pronounced genetic similarity among Nodularia spumigena strains evidencing their short evolutionary history. The studied Baltic Sea strains share similar sets of CRISPR-Cas cassettes and a higher number of insertion sequence (IS) elements compared to Nodularia spumigena CENA596 isolated from a shrimp production pond in Brazil. Nodularia spumigena UHCC 0039 proliferated similarly at three tested salinities, whereas the lack of salt inhibited its growth and triggered transcriptome remodeling, including the up-regulation of five sigma factors and the down-regulation of two other sigma factors, one of which is specific for strain UHCC 0039. Down-regulated genes additionally included a large genetic region for the synthesis of two yet unidentified natural products. Our results indicate a remarkable plasticity of the Nodularia salinity acclimation, and thus salinity strongly impacts the intensity and distribution of cyanobacterial blooms in the Baltic Sea.

Keywords: Baltic Sea, Cyanobacteria, Nodularia spumigena, Comparative genomics, RNA sequencing, Salinity

Received: 01 Aug 2017; Accepted: 14 Feb 2018.

Edited by:

George S. Bullerjahn, Bowling Green State University, United States

Reviewed by:

M J. Coolen, Curtin University, Australia
Theo Dreher, Oregon State University, United States  

Copyright: © 2018 Teikari, Hou, Wahlsten, Hess and Sivonen. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Prof. Wolfgang R. Hess, Spemann Graduate School of Biology and Medicine, University of Freiburg, Genetics & Experimental Bioinformatics, Schänzlestraße 1, Freiburg, D-79104, Germany, wolfgang.hess@biologie.uni-freiburg.de
Prof. Kaarina Sivonen, University of Helsinki, Department of Food and Environmental Sciences, Viikinkaari 9, Helsinki, FI-00014, Finland, kaarina.sivonen@helsinki.fi