Meta‐omic analyses of Baltic Sea cyanobacteria: diversity, community structure and salt acclimation

Abstract

Summary Cyanobacteria are important phytoplankton in the Baltic Sea, an estuarine‐like environment with pronounced north to south gradients in salinity and nutrient concentrations. Here, we present a metagenomic and ‐transcriptomic survey, with subsequent analyses targeting the genetic identity, phylogenetic diversity, and spatial distribution of Baltic Sea cyanobacteria. The cyanobacterial community constituted close to 12% of the microbial population sampled during a pre‐bloom period (June–July 2009). The community was dominated by unicellular picocyanobacteria, specifically a few highly abundant taxa (Synechococcus and Cyanobium) with a long tail of low abundance representatives, and local peaks of bloom‐forming heterocystous taxa. Cyanobacteria in the Baltic Sea differed genetically from those in adjacent limnic and marine waters as well as from cultivated and sequenced picocyanobacterial strains. Diversity peaked at brackish salinities 3.5–16 psu, with low N:P ratios. A shift in community composition from brackish to marine strains was accompanied by a change in the repertoire and expression of genes involved in salt acclimation. Overall, the pre‐bloom cyanobacterial population was more genetically diverse, widespread and abundant than previously documented, with unicellular picocyanobacteria being the most abundant clade along the entire Baltic Sea salinity gradient.

The Holocene sedimentary record of cyanobacterial glycolipids in the Baltic Sea: an evaluation of their application as tracers of past nitrogen fixation

“…The recurring late summer (JulyAugust) cHABs of the Baltic are dominated by the taxa Nodularia spumigena, Aphanizomenon flos-aquae and, to a minor extent, by Anabaena spp. and other species from the order Nostocales, family Nostocaceae (Hajdu et al, 2007;Hällfors, 2004;Kanoshina et al, 2003;Karjalainen et al, 2007;Sivonen et al, 2007;Celepli et al, 2017). While the Nodularia genus is usually prevalent, changes in the composition of the community have been observed from the early to the late stage of the cHAB and from one year to another, resulting in a large variation in its features over time (Finni et al, 2001;Hajdu et al, 2007;Kahru et al, 1994;Wasmund, 1997).…”

“…While the Nodularia genus is usually prevalent, changes in the composition of the community have been observed from the early to the late stage of the cHAB and from one year to another, resulting in a large variation in its features over time (Finni et al, 2001;Hajdu et al, 2007;Kahru et al, 1994;Wasmund, 1997). A recent extensive meta-omics study revealed that in the Baltic Proper (the predominant area for cHABs), 69 % of the heterocystous cyanobacteria belong to Aphanizomenon, 23 % to Anabaena and 8 % to Nodularia (Celepli et al, 2017).…”

“…However, this study used carotenoids (i.e., zeaxanthin and echinenone) that are not entirely specific to cyanobacteria and are certainly not limited to nitrogen-fixing cyanobacteria, as opposed to the highly specific HGs that were used here. For example, zeaxanthin is also produced by Synechococcus, the dominating unicellular cyanobacterial species in the Baltic Sea (Celepli et al, 2017). Furthermore, in this environment of highly variable sediment redox conditions, the effect of diagenesis should be considered.…”

“…(Celepli et al, 2017;Hajdu et al, 2007;Hällfors, 2004;Kanoshina et al, 2003;Karjalainen et al, 2007;Ploug, 2008;Sivonen et al, 2007). Deep-water anoxia, high phosphorus availability, calm water conditions and high irradiation resulting in a relatively high sea surface temperature (SST) have been identified as the main triggers for these blooms.…”

Identification of Cyanobacteria in a Eutrophic Coastal Lagoon on the Southern Baltic Coast

“…Other, but closely related, Synechococcus -like cyanobacteria succeed in eutrophic coastal waters (Caroppo, 2015 and references therein). The brackish waters are relatively little investigated so far (Celepli et al, 2017), but also show high abundances of APP and colonies with cells <2 μm. Thus, different cyanobacteria inhabit and can sometimes dominate almost all aquatic systems, even under highly contrasting conditions.…”