Structure and dynamics of bacterioplankton from Pampean shallow lakes

Bacterioplankton is an essential component for the functioning of aquatic ecosystems, plays a key role in the fundamental ecological processes for sustaining life and has a profound impact on the water quality of the aquatic environments. Therefore, it is important to expand knowledge in relation to the dynamic and genetic diversity of bacterioplankton in Pampean aquatic systems. The main objectives of this work were to evaluate the structure and dynamics of bacterioplankton from four Pampean shallow lakes located in the upper (Gómez and Carpincho) and lower (Chascomús and El Triunfo) basins of the Salado River, as well as to determine the influence of environmental factors on these communities. To achieve this, seasonal samplings were performed during one year (January 2015 - January 2016) in which main limnological variables were determined and the structure of bacterioplankton were analyzed by means of Illumina next-generation amplicon sequencing of the 16S rRNA gene. Bacterioplankton diversity indices were significantly higher in shallow lakes from the upper basin relative to those of the lower basin. Bacterioplankton richness was significantly lower in the clear-regime and disconnected shallow lake (El Triunfo) than in the turbid-regime and connected shallow lakes (Gómez, Carpincho and Chascomús). Bacterioplankton composition was different between all shallow lakes, except between the near and interconnected shallow lakes Gómez and Carpincho. Variations in the bacterioplankton composition of the studied shallow lakes were mainly explained by environmental variables such as total phosphorous, conductivity and Secchi depth. In addition, similarity in the bacterioplankton composition increased significantly with higher environmental similarity between lakes, and decreased with spatial distance between them. Our results showed that bacterioplankton structure of the studied lakes was ruled by environmental and spatial factors. The bacterial structure did not vary only between basins, but also between systems with different regimes and/or connections to the river.