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The ecological status of Pampean shallow lakes is evidenced by Cyanobacteria Harmful Blooms impairing these nutrient enriched, turbid and polymictic water bodies spread along the Central Plains of Argentina. Under the premise that shallow lakes are sentinels of global climate and eutrophication, a 3-year research in ten lakes located across a climatic gradient explored which factors drove the dynamics of cyanobacterial assemblages frequently driving to bloom prevalence. Contrarily to what is expected, the effect of seasonal temperature on cyanobacteria was subordinated to both the light environment of the water column, which was on turn highly affected by water level conditions, and to nutrient concentrations. Monthly samplings evidenced that cyanobacterial assemblages presented a broad-scale temporal dynamics mostly reflecting inter-annual growth patterns driven by water level fluctuations. Both species composition and biovolume gradually changed across a gradient of resources and conditions and hence, the scenario in each individual lake was unique with patterns at different temporal and spatial scales. More than 35 filamentous and colonial morphospecies constituted the assemblages of Pampean lakes: nostocaleans and chroococcaleans were inversely correlated in the prevailing interannual 3-cycled patterns., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Picocyanobacteria can occur as single-cell (Pcy) or as colonies (CPcy). Published evidence suggests that some Pcy strains have the capability to aggregate under certain culture conditions, however this has not been demonstrated to occur in natural environments. We investigated whether the Pcy and CPcy belong to the same species (i.e. phylotype), and the factors that determine their morphological and genetic variability in a hypertrophic shallow lake dominated by picocyanobacteria. Six main different morphologies and >30 phylotypes were observed. All sequences retrieved belonged to the 'Anathece + Cyanobium' clade (Synechococcales) that are known to have the capability of aggregation/disaggregation. The temporal variation of picocyanobacteria morphotype composition was weakly correlated with the DGGE temporal pattern, and could be explained by the composition of the zooplankton assemblage. Laboratory experiments confirmed that the small cladoceran Bosmina favoured the dominance of CPcy, i.e. Cyanodictyon doubled the size of the colonies when present, most likely through the aggregation of single-cell picocyanobacteria into colonies. Flow cytometry cell sorting and 16S rRNA + ITS sequencing of the Pcy and CPcy cytometrically-defined populations revealed that some phylotypes could be found in both sorted populations, suggesting phenotypic plasticity in which various Synechococcales phylotypes could be found in situ either as single-cells or as colonies., (© 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.)

The aim of this work was to study the components of the microbial food web and the degree of coupling between heterotrophic bacteria (HB) and heterotrophic flagellates (HF) in different shallow lakes of the Pampa Plain over a wide range of water transparency and nutrient levels. We hypothesized that not all microorganisms (i.e., HB, HF) equally increase with nutrient levels, thus, resulting in a weaker degree of coupling between HB and HF in more eutrophic waters. During the spring-summer 2009-2011, we sampled 40 Pampean lakes situated in different watershed of Buenos Aires Province. Abundances of most microbial components were very high, even higher than those reported in the literature. HB as well as picocyanobacteria (Pcy) increases with trophic state, while no clear relationship was found between protist (HF or ciliates) and Chl- a concentrations or nutrient levels. Photosynthetic picoplankton was generally dominated by phycocyanin-rich Pcy. Lakes with high HB and low HF were abundant, which suggest these components were weakly coupled. Based on the abundance of microorganisms, we do not accumulate enough evidence to segregate Pampean lakes into two discrete groups (clear vs turbid). [ABSTRACT FROM AUTHOR]