Vertical Distribution of Epibenthic Freshwater Cyanobacterial Synechococcus spp. Strains Depends on Their Ability for Photoprotection

Epibenthic cyanobacteria often grow in environments where the fluctuation of light intensity and quality is extreme and frequent. Different strategies have been developed to cope with this problem depending on the distribution of cyanobacteria in the water column. and either constant or enhanced levels of carotenoids were assayed in phycocyanin-rich strains collected from 1.0 and 0.5 m water depths. Protein analysis revealed that while the amount of biliproteins remained constant in all strains during light stress and recovery, the amount of D1 protein from photosystem II reaction centre was strongly reduced under light stress conditions in strains from 7.0 m and 1.0 m water depth, but not in strains collected from 0.5 m depth. spp. strains, depending on their genetically fixed mechanisms for photoprotection

Ecosystem-dependent adaptive radiations of picocyanobacteria inferred from 16S rRNA and ITS-1 sequence analysis

Small, coccoid and rod-shaped Synechococcus-type cyanobacteria with either phycoerythrin or phycocyanin as major accessory pigments were isolated from several large, temperate-zone lakes and the brackish Baltic Sea. The picocyanobacteria had two ribosomal operons with a long internal transcribed spacer (ITS-1) separating the 16S rDNA and 23S rDNA. A 16S rRNA-based phylogenetic analysis assigned all isolates to the picophytoplankton clade [sensu Urbach, E., Scanlan, D. J., Distel, D. L., Waterbury, J. B. & Chisholm, S. W. (1998). J Mol Evol 46, 188–201], which also comprises marine Synechococcus spp. and Prochlorococcus spp. The strains assorted to five paraphyletic clusters each containing two or more strains with 99·4–100 % 16S rRNA sequence identity. Five corresponding strain clusters were deduced from analysis of ITS-1 sequences. Sequence divergence in ITS-1 varied between 23 % in the most divergent and 1 % in the phylogenetically most conserved cluster. Clustered strains with low sequence divergence in ITS-1 were frequently isolated from a single ecosystem or hydrographically comparable lakes in the same region. They represent physiologically distinct ecotypes of species which, among other phenotypic variations, frequently differed in their major accessory pigments, the phycobiliproteins. The reproduction of the various pigment traits in different lineages was not correlated with the phylogenetic divergence deduced from 16S rRNA or ITS-1 sequences but rather seemed to be related to characteristics of the ecosystem and habitat from which the strains were isolated. The occurrence of a comparable spectrum of phenotypes in different lineages and ecosystems indicates that different strain clusters developed similar ecotypes during independent adaptive radiations.

Genetic diversity and distribution of periphytic Synechococcus spp. in biofilms and picoplankton of Lake Constance

In various water depths of the littoral zone of Lake Constance (Bodensee) cyanobacteria of the Synechococcus-type were isolated from biofilms (periphyton) on three natural substrates and an artificial one (unglazed tiles). From one tile three strains of phycoerythrin (PE)-rich Synechococcus spp. were isolated, the first examples of these organisms in the epibenthos. Phylogenetic inference based on the 16S–23S rRNA intergenic spacer (ITS-1) assigned all periphytic isolates to two clusters of the picophytoplankton clade (evolutionary lineage VI of cyanobacteria). The sequence divergence in the ITS-1 was used to design specific PCR primers to allow direct, culture-independent detection and quantification of isolated Synechococcus strains in natural periphytic and pelagic samples. Denaturing gradient gel electrophoresis (DGGE) analysis revealed depth-related differences of Synechococcus spp. distribution on tiles placed in the littoral zone. Synechococcus genotypes were observed which occurred in both the periphyton (on tiles) and in the pelagic picoplankton. A strain with one of these genotypes, Synechococcus sp. BO 8805, was isolated from the pelagic zone in 1988. Its genotype was found on tiles that had been exposed at different water depths in the littoral zone in spring and autumn of the year 2000. Quantitative analysis with a genotype-specific TaqMan probe and real-time Taq nuclease assays (TNA) confirmed its presence in the pelagic zone, although appearance of this and related genotypes was highly irregular and exhibited strong differences between consecutive years. Our results show that the ability to form significant subpopulations in pelagic and periphytic communities exists in three out of four phylogenetic clusters of Synechococcus spp. in Lake Constance. This versatility may be a key feature in the ubiquity of the evolutionary lineage VI of cyanobacteria. [KEYWORDS: Synechococcus-type picocyanobacteria; Periphyton; Denaturing gradient gel electrophoresis; Phylogenetic analysis; Quantitative Taq nuclease assay]