Novelty pattern determined for all clones obtained at the start and end of incubation experiments.

<p>Each circle represents one clone and its percent similarity to the closest environmental clone and the closest cultured species in GenBank. The mean similarity to both is indicated by the squares.</p

Phylogenetic affiliation of clones within cercozoans.

<p>Maximum-likelihood phylogenetic tree constructed with 77 partial and complete cercozoan sequences (1059 informative positions). For further description see legend of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041970#pone-0041970-g006" target="_blank">Figure 6</a>.</p

Comparison of 18S rRNA fingerprints at the start and end of three incubation experiments.

<p>(A) Stacked bar chart showing the relative intensity of the sequenced gel bands in each lane from filtered and unfiltered samples taken at the start and end of the incubation within the three experiments. Each color of the stacked bars represents one band and the length corresponds to the relative band intensity. (B) Numbered arrows indicate sequenced bands in the inverted DGGE image. (C) Information on the phylogenetic affiliation and trophic functions of sequenced bands with the band numbers referring to the bands in the DGGE image and the color code referring to the stacked bars chart.</p

Phylogenetic affiliation of clones within choanoflagellates.

<p>Maximum-likelihood phylogenetic tree constructed with 54 partial and complete choanoflagellate sequences (733 informative positions). Clades A–I follow the notation of del Campo and Massana <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041970#pone.0041970-delCampo1" target="_blank">[38]</a>. Four additional clades (J–M) are introduced. For further description see legend of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041970#pone-0041970-g006" target="_blank">Figure 6</a>.</p

Community shift towards heterotrophic taxa revealed by assignment of trophic functions to 18S rRNA sequences.

<p>The proportion of sequences assigned a trophic function (phototroph, heterotroph, unknown) at the start and end of incubation, as determined in clone libraries (A) and DGGE analysis (B).</p

Phylogenetic composition in clone libraries constructed from the three incubation experiments.

<p>Upper and middle panels show the composition of clones in the 3-µm filtered initial and final incubation samples, respectively. The unfiltered final incubation samples are represented by the lower panels. For each library, the proportion of clones within the major taxonomic groups is displayed as pie charts. A finer resolution of the taxonomic groups and their contribution to each library is shown in the bar charts.</p

Presentation_1_Phyto- and Bacterioplankton During Early Spring Conditions in the Baltic Sea and Response to Short-Term Experimental Warming.PDF

<p>Predicted increases in sea surface temperatures are expected to shift the balance between autotrophic production and the heterotrophic degradation of organic matter toward a more heterotrophic system. For early phytoplankton spring blooms at low water temperature the impact of rising temperatures has been mainly investigated in mesocosm experiments, while field observations are scarce. During a Baltic Sea research cruise we examined early spring bloom conditions, characterized by low temperatures (0–3°C), and performed on-board warming experiments to compare the responses of phyto- and bacterioplankton production to an increase in temperature. In the northern Baltic Sea, the low phytoplankton biomass indicated pre-bloom conditions. In the southern Baltic Sea, a diatom-dominated phytoplankton bloom with increased primary production (PP) occurred. Associated with this bloom were increases in bacterial production (BP) and bacterial abundance as well as shifts in bacterial community composition toward an increased proportion of Gammaproteobacteria and Bacteroidetes. However, the low BP/PP ratios (average: 1.2 ± 0.14%) indicated weak coupling between the bacterial and phytoplankton communities. Short-term warming (6 h, Δ+6°C) significantly enhanced PP (mean Q₁₀ 1.4) and especially BP (mean Q₁₀ 2.3). Hence, the higher water temperature increased both carbon flow into the bacterial community and bacterial processing of organic matter, thereby confirming previous experimental studies. By contrast, BP/PP ratios remained relatively low after warming (average: 1.7 ± 0.5%), unlike in previous mesocosm experiments performed at comparable temperatures and with similar plankton communities. Overall, these results imply that bacterial activities are suppressed during early phytoplankton blooms at low temperatures in the Baltic Sea and are not substantially altered by short-term warming events.</p

Cell number development in the course of three incubation experiments.

<p>(A) the abundance of total, high, and low nucleic acid containing bacteria (total, HNA, and LNA) for the 3-µm filtered and unfiltered treatments, respectively. (B) Cell numbers of <i>Synechococcus</i> (Syn), phototrophic eukaryotes (PE), and heterotrophic flagellates (HF) in the 3-µm filtered and unfiltered treatments. Error bars indicate the standard deviation in triplicate incubation bottles.</p

Image_1.PDF

<p>Salinity has a strong impact on bacterial community composition such that freshwater bacterial communities are very different from those in seawater. By contrast, little is known about the composition and diversity of the bacterial community in the sediments (bacteriobenthos) at the freshwater-seawater transition (mesohaline conditions). In this study, partial 16S-rRNA sequences were used to investigate the bacterial community at five stations, representing almost freshwater (oligohaline) to marine conditions, in the Baltic Sea. Samples were obtained from the silty, top-layer (0–2.5 cm) sediments with mostly oxygenated conditions. The long water residence time characteristic of the Baltic Sea, was predicted to enable the development of autochthonous bacteriobenthos at mesohaline conditions. Our results showed that, similar to the water column, salinity is a major factor in structuring the bacteriobenthos and that there is no loss of bacterial richness at intermediate salinities. The bacterial communities of marine, mesohaline, and oligohaline sediments differed in terms of the relative rRNA abundances of the major bacterial phyla/classes. At mesohaline conditions typical marine and oligohaline operational taxonomic units (OTUs) were abundant. Putative unique OTUs in mesohaline sediments were present only at low abundances, suggesting that the mesohaline environment consists mainly of marine and oligohaline bacteria with a broad salinity tolerance. Our study provides a first overview of the diversity patterns and composition of bacteria in the sediments along the Baltic Sea salinity gradient as well as new insights into the bacteriobenthos at mesohaline conditions.</p

Virus production (VP) in undiluted and virus dilution incubations.

<p>The figure shows VP at Gotland Deep (A) and Landsort Deep 1 (B) and 2 (C). Rates are given as average values of duplicate incubations in the oxic (OZ), suboxic (SZ), transition (TZ), and anoxic zone (AZ). Error bars represent the range of duplicate incubations.</p