Phenotypic plasticity in freshwater picocyanobacteria

Area of Science:

• Microbiology
• Limnology
• Ecology

Background:

• Picocyanobacteria exist as single cells (Pcy) or colonies (CPcy).
• Previous research suggested aggregation potential in Pcy under lab conditions, but not in natural settings.
• Understanding Pcy and CPcy variability is crucial in picocyanobacteria-dominated ecosystems.

Purpose of the Study:

• To investigate if Pcy and CPcy belong to the same species (phylotype).
• To identify factors influencing morphological and genetic variability of picocyanobacteria.
• To explore the aggregation/disaggregation capabilities of picocyanobacteria in a natural environment.

Main Methods:

• Investigated a hypertrophic shallow lake ecosystem.
• Utilized DGGE for genetic analysis and observed six distinct morphologies.
• Conducted laboratory experiments with zooplankton (Bosmina) and employed flow cytometry with 16S rRNA + ITS sequencing.

Main Results:

• Observed >30 phylotypes within the 'Anathece + Cyanobium' clade (Synechococcales).
• Picocyanobacteria morphotype composition correlated weakly with DGGE patterns and was influenced by zooplankton assemblages.
• Laboratory experiments showed Bosmina favored CPcy, with colonies doubling in size, suggesting Pcy aggregation.

Conclusions:

• Some Synechococcales phylotypes exhibit phenotypic plasticity, existing as both Pcy and CPcy in situ.
• Zooplankton, particularly Bosmina, can influence the transition from single cells to colonies.
• This study demonstrates Pcy aggregation into CPcy occurs in natural environments.