Dolichospermum lemmermannii (Cyanobacteria) in European waters: distribution patterns and toxic potential

Populations of Dolichospermum lemmermannii (Nostocales) have been widely identified in Central and Northern Europe. In Southern Europe, extended surface blooms of this species were recorded for the first time in Lake Garda in 1990/91. Since then, blooms of D. lemmermannii were documented in lakes Iseo (1990s), Maggiore (2005), and Como (2006). Recent studies have shown that populations collected in different water bodies are characterised by high variability to temperature adaptation. Actually, although this species is typical of cold environments, specific strains of D. lemmermannii show high temperature optima (i.e. between 19°C and 26°C). Further, in the large lakes south of the Alps, populations of Dolichospermum have the ability to form huge water blooms in summer stratified conditions and during calm weather. These results could suggest 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 16s rRNA and housekeeping genes (e.g. rpoB,) was integrated by the assessment of potential toxicity, evaluating the presence of cyanotoxins (i.e. Microcystins, Anatoxins, Saxitoxins) encoding genes. Further studies will allow gaining insight about the phylogeography of this fast spreading species at a continental level, along climatic gradients.