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.
Highlights
Photoautotrophic cyanobacteria have adapted to life in a wide range of aquatic and terrestrial habitats
Species diversity in brackish water ecosystems is usually relatively narrow because most organisms have adapted to life in either marine or freshwater environment (Telesh et al, 2013)
Cyanobacteria diversity is high in the brackish water Baltic Sea (Celepli et al, 2017) and, the underlying phenomena should be studied in much greater detail
Summary
Photoautotrophic cyanobacteria have adapted to life in a wide range of aquatic and terrestrial habitats. Salinity (referring here to the concentration of dissolved NaCl) is an important abiotic factor influencing prevailing cyanobacterial species distribution (Sivonen et al, 2007; Pade and Hagemann, 2014; Celepli et al, 2017). Proper strain-specific concentrations of inorganic salts have a crucial role in maintaining constant turgor pressure, while fluctuating salinity changes the water potential and inorganic ion concentration in cells (Hagemann, 2011). Increased salt concentration induces general stress responses such as the synthesis of chaperones and the arrest of photosynthetic activity and cell division (Kanesaki et al, 2002; Fulda et al, 2006; Qiao et al, 2013; Billis et al, 2014; Rai et al, 2014). Much less is known of how lower salinity affects cyanobacterial molecular responses and adaptation
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