Impact of a widespread herbicide on infectious disease dynamics in phytoplankton and fungi host-parasite interactions
Final Report Abstract
Water pollution, driven by human activities, threatens aquatic ecosystems worldwide. Metolachlor (MET), a widely used herbicide, is frequently detected in water bodies and can negatively affect non-target organisms, such as cyanobacteria, key players in aquatic trophic webs. Cyanobacterial growth is regulated by both abiotic and biotic factors, including parasitism by chytrids, which are the most important fungal parasites of phytoplankton. Cyanobacteria and chytrids are embedded in a complex network of interactions with other organisms, including heterotrophic bacteria. However, the effects of anthropogenic pollutants like MET on cyanobacterium-chytrid interactions and associated microbial communities remain largely unknown. This study investigated the effects of MET on the host-parasite system consisting of the toxigenic cyanobacterium Planktothrix agardhii and its chytrid parasite Rhizophydium megarrhizum. I focused on 1) the effects of MET on the infection dynamics of the cyanobacterium-chytrid system, 2) the transcriptional and metabolic responses of cyanobacteria and chytrids under MET exposure, and 3) changes in associated bacterial communities closely co-existing with cyanobacteria and chytrids. Results showed that continuous MET exposure did not significantly impact overall parasite fitness, although it reduces the size of chytrid reproductive structures. In uninfected cultures, MET promoted cyanobacterial growth, but this effect was overridden in cultures with parasitic infection. Pre-exposure of chytrids to MET resulted in temporary multi- and transgenerational detrimental effects on parasite fitness, which recovered after several generations without MET exposure. Metabolic response suggests that combined exposure to MET and chytrids induced oxidative stress in cyanobacteria, countered by non-enzymatic mechanisms, such as microcystins. Additionally, lipid peroxidation decreased in infected cyanobacteria. This decreases likely results from the reduced polyunsaturated fatty acid synthesis caused by MET, and reduced membrane surface area due to the destabilization from chytrid infection. While alpha and beta diversity of bacterial communities remained unchanged, differential abundance analysis revealed shifts in specific genera. For instance, Brevundimonas, a bacterium associated with toxigenic cyanobacteria, decreased only under MET exposure. Overall, this study highlights how MET influences cyanobacteriachytrid interactions and microbial communities, providing insights into the broader ecological effects of pollution on aquatic ecosystems.
Publications
-
Cigarette butts enable toxigenic cyanobacteria growth by inhibiting their lethal fungal infections. Ecotoxicology and Environmental Safety, 286, 117149.
Guttmann, Nele; Wolinska, Justyna; Spahr, Stephanie & Martínez-Ruiz, Erika Berenice
-
Widely used herbicide metolachlor can promote harmful bloom formation by stimulating cyanobacterial growth and driving detrimental effects on their chytrid parasites. Environmental Pollution, 344, 123437.
Martínez-Ruiz, Erika Berenice; Agha, Ramsy; Spahr, Stephanie & Wolinska, Justyna
