Soil Protists in Ecotoxicology ?! Development of an ecotoxicological assay using the testate amoeba Euglypha rotunda Nathalie Amacker a,c, Edward A.D. Mitchella,b, Nathalie Chèvrec a Laboratory
of Soil Biodiversity, University of Neuchâtel, Rue Emile Argand 11, CH-2000 Neuchâtel, Switzerland ; b Jardin Botanique de Neuchâtel, CH- 2000 Neuchâtel, Switzerland ; c Institut des dynamiques de la surface terrestre (IDYST), University of Lausanne, CH-1015 Lausanne, Switzerland
Introduction
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Most ecotoxicological studies focus on
Contact:
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Material & Methods
E. rotunda is grown with E. coli as carbon source in “Volvic” growth medium (i.e. Volvic water, KNO3,
metazoans (Lo, 2010; OECD, 2016) while the majority
of Eukaryotes are unicellular microorganisms known
KH2PO4, Na2SiO3 x 9H2O, Na-EDTA and soil extract) at
as protists. This discrepancy is particularly obvious for
12°C, in the dark; the cultures are exposed in triplicates to
the soil environment, sometime even referred as extreme end
a range of concentrations of S-metolachlor defined by a
of the Risk Assessment (Ockleford
preliminary test.
et al. 2017).
Protists are ubiquitous organisms of key functional roles
Test
in all ecosystems (Coûteaux & Darbyshire, 1998; Wilkinson, 2008). The
testate
amoeba
Euglypha
rotunda
(Rhizaria;
Euglyphida) is proposed as model organism as it is thought to have a cosmopolitan distribution and to be relatively abundant
Source: http://www.lgcstandards.com/CH/fr
(Clarke, 2003).
The herbicide S-Metolachlor, a member
Figure 1: Experimental design to test the effect of S-metolachlor
of the chloroacetanilides family, was used
on E. rotunda and E. coli. Pure E. coli cultures are monitored to
in this study. Its mode of action is to inhibit
investigate potential bacterial-pesticide interactions (e.g. growth
the very long chain fatty acids (VLCFAs)
inhibition, degradation of the pesticide).
synthesis. As the VLCFAs are essential
components of the cell membrane, this pesticide should lead to components
E. rotunda was counted weekly by direct observation under inverted microscope. E. coli was quantified weekly using a
a total inhibition of cell division.
microscopic counting chamber and via Colony Forming Units (CFUs) at the end of the test.
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Results & Discussion • The initial number of protozoa had to be 100-300 individuals to obtain exponential growth.
• The bacterial density did not influenced the protozoan growth. • The protozoa were affected in a non-linear way by Smetolachlor (Fig. 2). • The strongest effect was recorded at ca. 15 μg/L (Fig. 2). • The bacteria were not affected by S-metolachlor.
References
We believe that the experimental set-up proposed in the present Figure 2: Effect of different concentrations of S-metolachlor on E.
study allows reproducible results and could be developed as an
rotunda. The means and the standard error around the means
additional, accurate tool to assess the effect of pesticides and
(error bars) are displayed.
other pollutants on the soil ecosystem.
Coûteaux, M.-M., Darbyshire, J. F. (1998) Functional diversity among soil protozoa. Applied Soil Ecology. Vol 10, pp. 229-237. Clarke, K.J. (2003). Guide to the identification of soil protozoa - testate amoebae. FBA Spec. Publ. No. 12, p. 40. Lo, C.-C. (2010) Effect of pesticides on soil microbial community. Journal of Environmental Science and Health Part B. Vol. 45, pp. 348-359. DOI:10.1080/03601231003799804 OECD Guidelines for the Testing of Chemicals, Section 2, Effects on biotic systems. http://www.oecd-ilibrary.org/environment/ oecd-guidelines-for-the-testing-of-chemicals-section-2-effects-on-biotic-systems_20745761 (07.01.2016).
Ockleford, C., Adriaanse, P., Berny, P., Brock, T., Duquesne, S., Grilli, S., Hernandez‐Jerez, A.F., Bennekou, S.H., Klein, M., Kuhl, T., et al. (2017). Scientific Opinion addressing the state of the science on risk assessment of plant protection products for in‐soil organisms. EFSA J. 15, pp. 225. DOI:10.2903/j.efsa.2017.4690. Wilkinson, D. M. (2008) Testate amoebae and nutrient cycling: peering into the black box of soil ecology. Trends in Ecology and Evolution. Vol. 23 (11), pp. 596-599. doi:10.1016/j.tree.2008.07.006
