Enantiomer-Specific Malathion Degradation by Gut Microbes of the Colorado Potato Beetle

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Abstract Symbiotic microbes play pivotal roles in insect ecology, including the detoxification of insecticides, which reduces target host mortality and diminishes the efficacy of chemical pest control agents. Quantifying the prevalence of symbiont-mediated insecticide detoxification across the microbiome is necessary to understand its contributions to pesticide resistance, and to understand how pesticides alter gut microbial communities. Here, we investigated the prevalence and mechanisms of pesticide degradation within the gut microbiota of the Colorado potato beetle ( Leptinotarsa decemlineata ), a significant agricultural pest that has driven ongoing insecticide innovation for decades. Beetles were collected from an organic farm in Tyler, TX, and 18 bacterial isolates representing the diversity of their gut microbiota were screened for their ability to degrade three common insecticides in vitro : imidacloprid, fenitrothion, and malathion. Among these, Acinetobacter calcoaceticus, Pseudomonas protegens , and an unnamed Microbacterium species degraded malathion as a sole carbon source, with distinct enantiomer-specific preferences. Untargeted GC-MS analysis revealed breakdown products, providing initial insights into the metabolic pathways utilized by these microbes. These findings suggest that microbial association with resistant insect hosts may select for microbial insecticide utilization, potentially enhancing resistance development in agricultural pests and influencing the surrounding soil microbiome.

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