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.

The use of cyanobacterial whole-cell luminescent bioreporters has enhanced our ability to monitor nutrient availability in aquatic ecosystems. We have constructed a Synechocystis sp. strain PCC6803 bioluminescent reporter for the assessment of nitrate bioavailability. Specifically, a 380-base pair DNA fragment containing the NtcA/B-dependent nitrate/nitrite-activated nirA promoter (regulating expression of genes encoding nitrite reductase) was fused to the bacterial luciferase genes, luxAB, and introduced into Synechocystis by genetic transformation. Characterization of this strain, designated AND100, yielded dose-dependent increased bioluminescence coincident with increased nitrate added to the growth medium from 1 to 100 µM. Bioluminescence in response to nitrate addition was light dependent up to 50 µmol quanta m -2 s -1

We previously developed a luminescent Synechococystis sp. strain PCC 6803 cyanobacterial bioreporter that is used as a real-time whole-cell sensor to assess nitrate assimilatory capacity in freshwaters. Applying the bioreporter assay to Lake Superior, a system whose nitrate levels have increased 6-fold since 1900, we investigated factors that constrain nitrate utilization in this oligotrophic system. Clean sampling methods were used to collect water from Lake Superior during spring and summer 2004, and nitrate utilization was measured by monitoring bioreporter luminescence. Bioreporter response was monitored during experiments in which the lake water was amended with nutrients and incubated under light regimes simulating integrated spring and summer mixing depths. These studies demonstrated that nitrate utilization was enhanced at most stations following addition of phosphorus (P). Moreover, at many stations, addition of iron (Fe) enhanced the P effect. Strength-of-effect statistical analysis provided the individual contribution of P and Fe toward stimulating bioreporter response. In general, distance from shore and season were not good predictors of nitrate assimilatory capacity. Manipulation of light flux during bioreporter experiments also showed that light intensities experienced during spring mixing are likely insufficient to saturate the rate of nitrate utilization. Overall, these data suggest that P-limited algae are deficient in their ability to assimilate nitrate in Lake Superior. Furthermore, we suggest that a secondary limitation for Fe may occur that further constrains nitrate drawdown. Lastly, during spring, light fluxes are sufficiently low to prevent maximal nitrate utilization, even in the absence of nutrient limitation.

No abstract

Green cyanobacteria differ from the blue–green cyanobacteria by the possession of a chlorophyll-containing light-harvesting antenna. Three genera of the green cyanobacteria namely Acaryochloris, Prochlorococcus, and Prochloron are unicellular and inhabit marine environments. Prochlorococcus marinus attracts most attention due to its prominent role in marine primary productivity. The fourth genus Prochlorothrix is represented by the filamentous freshwater strains. Unlike the other green cyanobacteria, Prochlorothrix strains are remarkably rare: to date, living isolates have been limited to two European locations. Taking into account fluctuating blooms, morphological resemblance to Planktothrix and Pseudanabaena, and unsuccessful attempts to obtain enrichments of Prochlorothrix, the most successful strategy to search for this cyanobacterium involves PCR with environmental DNA and Prochlorothrix-specific primers. This approach has revealed a broader distribution of Prochlorothrix. Marker genes have been found in at least two additional locations. Despite of the growing evidence for naturally occurring Prochlorothrix, there are only a few cultured strains with one of them (PCC 9006) being claimed to be axenic. In multixenic cultures, Prochlorothrix is accompanied by heterotrophic bacteria indicating a consortium-type association. The genus Prochlorothrix includes two species: P. hollandica and P. scandica based on distinctions in genomic DNA, cell size, temperature optimum, and fatty acid composition of membrane lipids. In this short review the properties of cyanobacteria of the genus Prochlorothrix are described. In addition, the evolutionary scenario for green cyanobacteria is suggested taking into account their possible role in the origin of simple chloroplast.

No abstract

No abstract

Microarray-based expression profiling of living systems is a quick and inexpensive method to obtain insights into the nature of various diseases and phenotypes. A typical microarray profile can yield hundreds or even thousands of differentially expressed genes and finding biologically plausible themes or regulatory mechanisms underlying these changes is a non-trivial and daunting task. We describe a novel approach for systems-level interpretation of microarray expression data using a manually constructed “overview” pathway depicting the main cellular signaling channels (Atlas of Signaling). Currently, the developed pathway focuses on signal transduction from surface receptors to transcription factors and further transcriptional regulation of cellular “workhorse” proteins. We show how the constructed Atlas of Signaling in combination with an enrichment analysis algorithm allows quick identification and visualization of the main signaling cascades and cellular processes affected in a gene expression profiling experiment. We validate our approach using several publicly available gene expression datasets.