Distribution patterns and toxic potential of Dolichospermum lemmermannii (Cyanobacteria) in European water bodies

The presence of Dolichospermum lemmermannii (Nostocales) in Central and Northern Europe is well documented. Albeit this species is typical of cold environments, it is characterised by high variability to temperature adaptation as well. Some populations of D. lemmermannii show high temperature optima (i.e. between 19°C and 26°C) and have the capability to form huge water blooms in summer stratified conditions and during calm weather. In Southern Europe, a case of recent colonisation is represented by the spread of this species to the large and deep lakes south of the Alps (namely, lakes Garda, Iseo, Como and Maggiore). Dolichospermum appeared for the first time in Lake Garda at the beginning of the 1990s with extended blooms between July and September. Afterwards it appeared in lakes Iseo (second half of the 1990s), Maggiore (2005), and Como (2006). The spread highlighted the ecological heterogeneity of D. lemmermannii, possibly suggesting the existence of different ecotypes adapted to different European climatic regions. In this work, we report the preliminary results of a wide research carried out on populations isolated from different European waterbodies. The analyses are based on taxonomical, genetic and metabolomic determinations carried out on isolated strain cultures. A phylogenetic study on the 16S rRNA and housekeeping genes (e.g. rpoB,) was integrated by the assessment of the toxic potential, evaluating the presence of cyanotoxins (i.e. microcystins, nodularins, anatoxins, cylindrospermopsins) and cyanotoxins encoding genes. Further studies will allow gaining insight about the phylogeography of this fast spreading species at a continental level, along climatic and trophic gradients.