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.; ESCARAY R.; ACINAS S. G.; GASOL J. M.

Torino

Congreso; XXXIII Congress SIL 2016; 2016

International Society of Limnology.

Single-cellpicocyanobacteria (Pcy) are frequently accompanied by colonies of Pcy-likecells embedded within a mucilaginous sheath (CPcy). Some evidences suggestedthat many Pcy have the capability to aggregate under certain cultureconditions. The aim of this study is to disentangle the diversity of coccoidscyanobacteria linking morphological, ecological and molecular information. Weperformed a polyphasic approach in a hypertrophic shallow lake dominated bycoccoids cyanobacteria in order to test the hypothesis that dominant genotypesare present either as single-cell or colonies, whereas their morphologicalstructure (relative abundance of Pcy and CPcy) is mainly driven by zooplanktoncomposition. Autotrophic picoplankton was almost exclusivelyrepresented by ficocianine-rich Synechococcus-like cells (Pcy). The nanoplanktonic fraction was dominated bycolonial coccoids of cyanobacteria (Aphanocapsa?like, Eucapsis sp. andCyanodictyon sp.), together withmicrocolonies of Pcy-like cells and short trichomes. Zooplanktonassemblage had a strong structuring effect on the composition of thesecyanobacteria morphotypes. The small cladoceran Bosmina favoured the dominance of CPcy without affecting the totalamount of cells. Cyanodictyon doubledtheir colonial size under its presence. Most likely this zooplankter promotedthe aggregation of Pcy into CPcy as an anti-grazing strategy. All 16S rDNA sequencesretrieved belonged to the ?Cyanobium +Anathece? clade (Synechococcaceae). Manystrains within this family have the capability to aggregate/disaggregatedepending on the environmental conditions. Flow cytometry sorting andsequencing of Pcy and CPcy revealed that most sequences recovered were found inboth sorted populations, confirming that various Synechococcaceae genotypes canbe found in situ either assingle-cells or colonies.