From bystander to key player: unveiling the gut microbiota’s role in mediating cyanobacterial toxicity in aquatic animals

Cyanobacterial blooms represent one prevalent stressor in aquatic ecosystems worldwide, exposing aquatic animals to complex mixtures of live cells and dissolved bioactive compounds, including cyanotoxins. The gut microbiota, which plays fundamental roles in digestion, immunity, and metabolic regulation, has been recognized as a key interface between environmental stressors and host health. Exposure to cyanobacteria occurs primarily through ingestion, making the gut the main site of interaction with live cells, cyanobacterial metabolites, and associated bacteria. While dissolved bioactive compounds can also penetrate via gills and skin, their role is secondary in most animals. Understanding how cyanobacteria interact with the host gut microbiota is therefore essential to fully assess their impacts on animal health. This review summarizes current knowledge of gut microbiota responses to cyanobacterial stress in crustaceans, mollusks, and chordates, highlighting dynamic and context-dependent changes in microbial communities. We discuss the cascading effects on host physiology, immune function, and metabolic homeostasis, and explore how the microbiota may modulate host resilience, including potential roles in cyanotoxin degradation.