Aetokthonos hydrillicola is an epiphytic cyanobacterium found on the abaxial leaf surfaces of aquatic weeds. This species of cyanobacterium is responsible for aetokthonotoxin (AETX), which is biosynthesized from a six gene cluster (aetA-F) in the presence of bromine. The neurotoxin is ingested by coots and waterfowl consuming submerged weeds contaminated with the algae; bald eagles are subsequently impacted when preying on these afflicted birds. The disease, termed Avian Vacuolar Myelinopathy (AVM), is not limited to birds and can affect higher-order organisms including humans in the food chain. There are currently no similar gene clusters available in the National Center for Biotechnology Information (NCBI) database. We traced the origin of at least a member of aetX operon using state-of-the-art bioinformatics tools and ecological factors. Our study demonstrates that Aetokthonos hydrillicola acquired members of aetX operon from external sources via horizontal gene transfer. Specifically, aetA through aetF were acquired from Anabaena sp., Nodularia sphaerocarpa UHCC 0038, Calothrix sp. PCC 7716 (for both aetC and aetD), Chloroflexota bacterium isolate bin156, and Lyngbya majuscule, respectively. These events occurred sequentially, rather than simultaneously, in the order of aetA, aetD, aetE, aetB, aetC, and aetF from earliest to the most recent event that occurred no later than 1994. We infer that these transfers were driven by environmental pressure from aquatic grazers, which depleted host availability.