Linking molecular and morphological diversity of unicellular and colonial picocyanobacteria in a hypertrophic shallow lake

UNREIN, F.; HUBER, M. P.; DIOVISALVI, N.; FERRARO, M.; METZ, S.; LAGOMARSINO, L.; LLAMES, M. E.; ROYO-LLONCH, M.; BUSTINGORRY, J. F.; ESCARAY, R.; ACINAS, S.; GASOL, J. M.

Congreso; SIL 2016; 2016

SIL

Single-cell picocyanobacteria (Pcy) are frequently accompanied by colonies of Pcy-like cells embedded within a mucilaginous sheath (CPcy). Some evidences suggested that many Pcy have the capability to aggregate under certain culture conditions. The aim of this study is to disentangle the diversity of coccoids cyanobacteria linking morphological, ecological and molecular information. We performed a polyphasic approach in a hypertrophic shallow lake dominated by coccoids cyanobacteria in order to test the hypothesis that dominant genotypes are present either as single-cell or colonies, whereas their morphological structure (relative abundance of Pcy and CPcy) is mainly driven by zooplankton composition. Autotrophic picoplankton was almost exclusively represented by ficocianine-rich Synechococcus-like cells (Pcy). The nanoplanktonic fraction was dominated by colonial coccoids of cyanobacteria (Aphanocapsa?like, Eucapsis sp. and Cyanodictyon sp.), together with microcolonies of Pcy-like cells and short trichomes. Zooplankton assemblage had a strong structuring effect on the composition of these cyanobacteria morphotypes. The small cladoceran Bosmina favoured the dominance of CPcy without affecting the total amount of cells. Cyanodictyon doubled their colonial size under its presence. Most likely this zooplankter promoted the aggregation of Pcy into CPcy as an anti-grazing strategy. All 16S rDNA sequences retrieved belonged to the ?Cyanobium + Anathece? clade (Synechococcaceae). Many strains within this family have the capability to aggregate/disaggregate depending on the environmental conditions. Flow cytometry sorting and sequencing of Pcy and CPcy revealed that most sequences recovered were found in both sorted populations, confirming that various Synechococcaceae genotypes can be found in situ either as single-cells or colonies.