Unravelling anatoxin-a in the large lakes south of the Alps: Occurrence and toxic potential of Tychonema (Cyanobacteria)

The investigations carried out in the largest lakes south of the Alps (Garda, Iseo, Como and Maggiore) have demonstrated, besides the widespread occurrence of microcystins (MCs), the presence of significant concentrations of anatoxin-a (ATX). Genetic analyses and metabolomic profiling of strains isolated from Lake Garda allowed excluding both Dolichospermum lemmermannii and Planktothrix rubescens among the potential producers of ATX. P. rubescens is the dominant cyanobacterium in the deep subalpine lakes. From the other side, extended surface blooms of D. lemmermannii were recorded for the first time in Lake Garda in 1990/91, and successively in the other deep southern subalpine lakes. The problem arising from the production of ATX without the apparent identification of a toxin producer was elucidated in Lake Garda in the spring 2014. During the isolation of cyanobacteria filaments, several strains of Tychonema bourrellyi (Oscillatoriales) were identified and cultivated. Successive analyses demonstrated that this species was able to produce consistent amounts of ATX. This was confirmed also by the amplification of genes involved in the biosynthesis of ATX and by the discovery of ATX producing populations of T. bourrellyi and T. bornetii in Norwegian waterbodies. Preliminary analyses, still in progress, are demonstrating that similar populations of Tychonema able to synthetize ATX are present also in the other largest lakes south of the Alps. In this contribution we will evaluate i) the taxonomic attribution of several Oscillatoriales strains in the subalpine lake district by phylogenetic analyses, and ii) the toxic potential of populations by metabolomic profiling and genetic analyses.