sxtA-Based Quantitative Molecular Assay To Identify Saxitoxin-Producing Harmful Algal Blooms in Marine Waters

Abstract

ABSTRACTThe recent identification of genes involved in the production of the potent neurotoxin and keystone metabolite saxitoxin (STX) in marine eukaryotic phytoplankton has allowed us for the first time to develop molecular genetic methods to investigate the chemical ecology of harmful algal bloomsin situ. We present a novel method for detecting and quantifying the potential for STX production in marine environmental samples. Our assay detects a domain of the genesxtAthat encodes a unique enzyme putatively involved in thesxtpathway in marine dinoflagellates,sxtA4. A product of the correct size was recovered from nine strains of four species of STX-producingAlexandriumandGymnodinium catenatumand was not detected in the non-STX-producingAlexandriumspecies, other dinoflagellate cultures, or an environmental sample that did not contain known STX-producing species. However,sxtA4was also detected in the non-STX-producing strain ofAlexandrium tamarense, Tasmanian ribotype. We investigated the copy number ofsxtA4in three strains ofAlexandrium catenellaand found it to be relatively constant among strains. Using our novel method, we detected and quantifiedsxtA4in three environmental blooms ofAlexandrium catenellathat led to STX uptake in oysters. We conclude that this method shows promise as an accurate, fast, and cost-effective means of quantifying the potential for STX production in marine samples and will be useful for biological oceanographic research and harmful algal bloom monitoring.