Development of a quantitative PCR assay to detect Gambierdiscus holmesii, a ciguatoxin producing species from Australian waters.

A quantitative polymerase chain reaction (qPCR) assay was developed for the species-specific detection and quantification of Gambierdiscus holmesii, recently reported to produce known ciguatoxin (CTX) analogues in north Queensland. The assay was designed to target the ITS region and calibrated using synthetic gBlocks standards and cell-based standard curves to enable accurate quantification. The G. holmesii-specific qPCR assay demonstrated high specificity, efficiency, and sensitivity, with no cross-reactivity observed against closely related Gambierdiscus species. The assay was subsequently applied to environmental samples collected from Heron Island (Great Barrier Reef, Queensland), detecting G. holmesii in 5 out of 12 sites. This newly developed molecular tool enhances the capacity to monitor G. holmesii in the environment and supports improved surveillance of ciguatoxin-producing Gambierdiscus species in Australian waters, enabling earlier detection and more effective management of ciguatera poisoning risks to public health and fisheries.