Bacterioplankton community and population changes following pesticide-induced stress in semi-natural mesocosms

Espèces nuisibles et pesticides
vendredi 20 déc. 03:55 PM (15 minutes)
Salle CD

Freshwater habitats are commonly disturbed by agricultural contaminants used in their watershed. They can affect the bacterioplankton, that rapidly reacts to disturbances, and are thus indicators of ongoing changes. Despite a general deterioration of freshwater quality due to these changes, we lack an understanding of how the interaction of multiple agricultural contaminants affects aquatic ecosystems. Here we describe an experiment performed on the LEAP (Large Experimental Array of Ponds) platform, containing mesocosms filled with water from Lake Hertel, at the Gault Nature Reserve. The experimental ponds were divided into groups that received a low or a high amount of nutrients and, within each nutrient treatment, pulse perturbations of the herbicide Roundup and the insecticide imidacloprid were applied either alone or in combination in a factorial design. We assessed bacterial community changes over the eight-weeks experiment through 16S rRNA gene amplicon sequencing, carbon utilization assays, and cell counts. We further selected a subset of the most responsive treatments and performed shotgun metagenomic sequencing to track polymorphism and potential adaptive evolution within certain bacteria. Imidacloprid and nutrients had less impact than glyphosate, which selected for lineages in the phylum Proteobacteria, such as the Rhizobiaceae. Despite increasing in relative abundance in response to glyphosate, metagenome-assembled genomes (MAGs) of Rhizobiaceae maintained stable levels of polymorphism over time, suggesting that they were not subject to genome-wide selective sweeps. Together, these results suggest that species sorting plays a greater role than adaptive evolution in the bacterial community response to glyphosate, at least over short time scales.

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