Detection of cyanobacterial sxt genes and paralytic shellfish toxins in freshwater lakes and brackish waters on Aland Islands, Finland

Abstract Harmful cyanobacteriaare a globally growing concern. They produce a large variety of toxic compounds, including saxitoxinand its many structural variants, a group of potent neurotoxins collectively called paralytic shellfish toxinsor PST. Nucleic acid based detection methods, such as qPCR, have been proposed as potential screening and monitoring tools for toxic cyanobacteria, but it is not clear how well the presence and quantity of saxitoxinbiosynthesis ( sxt ) genes can be used to predict the production of PST in the environment. In this study, the prevalence of three sxt genes and their co-occurrence with paralytic shellfish toxinsin the environment was investigated. The sxtA , sxtG and sxtB genes were present on average in 31% of the samples collected from lakes and brackish coastal waters on Aland Islands, Finland, during the three-year monitoring period. PST detection frequency varied from 13% to 59% from year to year, and concentrations were generally low. On average higher sxtB copy numbers were associated with PST detection, and although a positive correlation between gene copy numbers and toxin concentrations was observed (Spearman rank correlation, ρ = 0.53, P = 0.012), sxt gene presence or quantity didn’t reliably predict PST production. Sequencing of sxtA fragments and identification of main cyanobacteriaindicated that the likely candidate responsible for PST production in the samples belonged to the genus Anabaena.