ROLE OF MICROBIAL SYMBIONTS IN THE ADAPTATION OF INSECTS TO METAL-CONTAMINATED ENVIRONMENTS

Abstract

Heavy metal contamination poses a significant ecological threat, particularly to insects that serve as vital contributors to ecosystem functioning. This study investigates the functional role of microbial symbionts in enhancing insect tolerance to metal-contaminated environments through a combination of field sampling, microbiome sequencing, metal accumulation assays, and gene expression analysis. Insects from highly polluted sites exhibited significantly elevated body burdens of cadmium, lead, arsenic, and zinc, with Coleoptera and Diptera accumulating the highest concentrations. Comparative microbiome profiling revealed a dominance of metal-resistant genera, such as Pseudomonas and Bacillus, in insects from contaminated habitats, while control-site insects showed higher proportions of Lactobacillus. Functional metagenomics identified an enrichment of genes associated with metal efflux pumps, oxidoreductases, and metallothionein-like proteins in symbiotic microbiota of contaminated-site insects. Host physiological analysis showed upregulation of detoxification genes including Catalase, SOD, and MtnA, indicating a coordinated stress response. Microbial transplantation experiments further demonstrated that tolerant-associated microbiota could partially confer metal resistance to susceptible insect hosts, highlighting the causal role of symbionts in adaptation. Collectively, the results support the hypothesis that microbial symbionts are integral to insect survival under heavy metal stress, influencing both physiological and ecological outcomes. These findings advance our understanding of host–microbe–environment interactions and have important implications for bioindication, ecological resilience, and symbiont-assisted remediation strategies in contaminated ecosystems.