Pesticides impact microbial communities in the freshwater ecosystem: Implications on biogeochemical cycles

Pesticides that discharge from surrounding environments into river water affect the composition and structure of the microbiome, eventually modifying the biogeochemical processes. Microcosm experiments examined the effects of two prevalent pesticides (malathion and atrazine) on the river water microbiome. 16S rRNA gene amplicon sequencing was leveraged to characterize microbiome shifts in the presence and absence of pesticides. Microbial diversity was significantly reduced in the presence of pesticides. The presence of malathion and atrazine in higher abundances promoted the growth of Pseudomonas while inhibiting the expansion of other microorganisms. Principal Coordinate Analysis indicated compelling differences in diversity and metabolic profiles. Shifts in microbial populations involved in carbon, nitrogen, and sulfur cycles were observed in the presence of pesticides. Our findings demonstrated a reduction in microbial populations involved in carbon fixation and sulfur oxidation in samples exposed to pesticides compared to samples unamended with pesticides. With respect to the nitrogen cycle, the microorganisms involved in nitrification and denitrification processes were reduced in the presence of pesticides. This study exemplifies an intricate interplay between pesticide application, microbial diversity, and the associated metabolic activities, which highlights the multifaceted impact of emerging contaminants that contribute to a cascading effect on the biogeochemical cycles. • The river water microbiome preferentially degraded malathion over atrazine. • Exposure to atrazine and malathion led to a decline in microbial diversity. • Atrazine and malathion exerted distinct effects on the microbial community. • Pseudomonas was enriched in the presence of atrazine and malathion. • Carbon-fixing microorganisms were reduced in the presence of pesticides.