Lake Superior Supports Novel Clusters of Cyanobacterial Picoplankton

Abstract

Very little is known about the biodiversity of freshwater autotrophic picoplankton (APP) in the Laurentian Great Lakes, a system comprising 20% of the world's lacustrine freshwater. In this study, the genetic diversity of Lake Superior APP was examined by analyzing 16S rRNA gene and cpcBA PCR amplicons from water samples. By neighbor joining, the majority of 16S rRNA gene sequences clustered within the "picocyanobacterial clade" consisting of freshwater and marine Synechococcus and Prochlorococcus. Two new groups of Synechococcus spp., the pelagic Lake Superior clusters I and II, do not group with any of the known freshwater picocyanobacterial clusters and were the most abundant species (50 to 90% of the sequences) in samples collected from offshore Lake Superior stations. Conversely, at station Portage Deep (PD), located in a nearshore urbanized area, only 4% of the sequences belonged to these clusters and the remaining clones reflected the freshwater Synechococcus diversity described previously at sites throughout the world. Supporting the 16S rRNA gene data, the cpcBA library from nearshore station PD revealed a cosmopolitan diversity, whereas the majority of the cpcBA sequences (97.6%) from pelagic station CD1 fell within a unique Lake Superior cluster. Thus far, these picocyanobacteria have not been cultured, although their phylogenetic assignment suggests that they are phycoerythrin (PE) rich, consistent with the observation that PE-rich APP dominate Lake Superior picoplankton. Lastly, flow cytometry revealed that the summertime APP can exceed 10 5 cells ml ؊1 and suggests that the APP shifts from a community of PE and phycocyanin-rich picocyanobacteria and picoeukaryotes in winter to a PE-rich community in summer.

Colorful microdiversity of Synechococcus strains (picocyanobacteria) isolated from the Baltic Sea

“…Studies on large ecosystems, such as Lake Superior and the Baltic Sea, indicate that locally adapted Synechococcus spp. inhabit these environments (Ivanikova et al, 2007;Haverkamp et al, 2008). This is consistent with the conclusions of Pommier et al (2007), who found signals of endemism within the global bacterioplankton community.…”

Periodic picophytoplankton predominance in a large, shallow alkaline lake (Lake Fertő, Neusiedlersee)

“…3 and 4). Although group B and group C picocyanbacteria seemed to have limited distribution (Robertson et al, 2001;Ernst et al, 2003), increased picoplankton investigations revealed a more widespread occurrence of these groups (Crosbie et al, 2003;Ivanikova et al, 2007;Haverkamp et al, 2008;Sa´nchez-Baracaldo et al, 2008;this study). This widespread dispersal of some closely related picocyanobacterial phylotypes may confirm the high adaptive potential of these groups.…”

Actinorhodopsin genes discovered in diverse freshwater habitats and among cultivated freshwater Actinobacteria

“…Lake Superior biomass was obtained during a research cruise on the R/V Blue Heron in June 2005 during isothermal mixing of the water column. Water was collected from a depth of 25 m at station Castle Danger 1 (CD1; 47.301N, 91.671W; see Ivanikova et al (2007) for sampling details). Biomass was collected from the central basin of Lake Erie (Environment Canada Station 84, 411 56 0 46 00 N, 811 38 0 46 00 W) during a July 2005 cruise aboard the CCGS Limnos when the water column was thermally stratified (for sampling details see Wilhelm et al, 2006).…”

“…The other two samples originated from the North American Great Lakes. Here we concentrate our efforts on samples from Lakes Superior and Erie previously obtained for diversity studies of cyanobacterial picoplankton (Wilhelm et al, 2006;Ivanikova et al, 2007). Lake Superior represents a unique environment because its waters are extremely phosphate limited, contributing to low rates of primary production similar to non-bloom conditions at the Bermuda Atlantic Time Series Site (RW Sterner, personal communication).…”