Making waves: Cyanopeptides as a potential defence against chytrid parasites in cyanobacteria.

Cyanobacteria are foundational components of aquatic ecosystems that frequently form dense blooms. Many of them produce toxic secondary metabolites that threaten ecological integrity, human and animal health and water quality. Chytrid fungi, widespread parasites of phytoplankton, can alter community composition and succession through selective infection, with potential to reduce bloom persistence by increasing host mortality. However, chytrid infection rates in cyanobacteria remain markedly lower than in other phytoplankton groups, raising a key question: what underlies the reduced susceptibility of cyanobacteria to chytrid parasitism? Evidence indicates that chytrid infection could be associated with the production of cyanobacterial oligopeptides involved in defence or stress responses, many of which possess cytotoxic or enzyme-modulating properties with direct relevance to water quality. Infection-driven cell lysis can further accelerate bloom collapse and release intracellular metabolites that pose a threat to global water management. However, direct experimental evidence linking these oligopeptides to anti-chytrid defence remains scarce and the topic is still poorly represented in the literature. This article explores the potential for oligopeptide-based defence against chytrids and evaluates how chytrid-induced metabolite production may represent an under-recognised contribution to chemical variability in aquatic systems.