Pesticides toxicity at the soil food-web level: Defining effects on microbial predator-prey systems

Toxicity of pesticides to natural ecosystems has been a constant concern, however, ecotoxicological assessments have mostly focused on aquatic organisms and terrestrial macro-organisms. Little is known about the impact of pesticides on soil microbial networks including microbial predators (i.e., protists). This is particular important, since interactions between microbial predators and prey influence bacterial diversity, productivity, plant growth and the flux of nutrients to several trophic levels. With my PhD project we aim to evaluate the toxic effect of pesticides in a microbial food web context, i.e. depending on the presence and complexity of microbial predator-prey interactions. To do so, in gamma-sterilised soils we assembled microbial communities with increasing complexity of predator-prey interactions and exposed them to different pesticides. Functional aspects are being addressed along the time as well as changes in microbial community composition and abundances of functional groups, to shed light on the bacterial and microbial response to pesticide exposure in soil and the role of microbial trophic complexity in this response.

Experimental setup

Fig. 1: Experimental setup of the ESR6 microcosms experiment. Briefly in gamma-sterilised soils we assembled microbial communities with increasing complexity of predator-prey interactions: i. bacteria only (extracted from natural soil), ii. bacteria + selected bacterivorous flagellate protists and iii. bacteria + several protists with different feeding modes and exposed them to different pesticide treatments: i. No pesticide, ii. 1X Acetamiprid iii. 1X Etridiazole. Functional aspects are being addressed along the time as well as changes in microbial community composition and abundances of functional groups.

In my PhD I am studying whether and how the presence of pesticides affects soil microbial communities, more specifically looking at the predator-prey interactions between protists and bacteria.

Fig. 2: Preparing sample extracts for the analysis of chemical parameters and sampling the soil microcosm.


Microscopy


Fig. 3: Image of the one of the protist used in the microcosms experiment. Tetrahymena spp. in axenic culture. Magnification 20X.
Fig 4: Representative HR-SEM (HE-SE2 detector) image of Tetrahymena sp., a ciliate protist introduced in the microcosms as a micro-predator. Magnification 2500X


Assays


Fig. 5: . MicroResp method for determining Substrate Induced Respiration (SIR) in the soil microcosms. Detection plate after incubation with the soil.
Fig 6: MicroResp method for determining Substrate Induced Respiration (SIR) in the soil microcosms. Deep well plate containing the soil connected with the detection plate.


Conference


Fig. 7: Poster
Fig. 8: ESR6 Marta Pérez Villanueva with her poster presented at the 3rd International Conference in Microbial Ecotoxicology - Ecotoxicomic 2022 in Montpellier, France.