Taxonomy and production of paralytic shellfish toxins by the freshwater cyanobacterium Aphanizomenon gracile LMECYA40

Detection of Paralytic Shellfish Toxins (PST) in an algal bloom in a Portuguese drinking water reservoir (Lake Crato) was followed by isolation of a strain of Aphanizomenon gracile. The strain, coded as LMECYA40, was cultured and identified by combining a morphological study with 16S rRNA gene sequencing. The toxin profile of this isolate, as revealed by HPLC-FLD analysis, was similar to that of other Aphanizomenon strains (e.g. NH-5) isolated from North America, consisting of two PST analogues: neoSTX (0.27 fmol cell(-1)) and STX (0.05 fmol cell(-1)). Based on these toxin levels, we estimated that a culture with a cell density of 10(7) cells ml(-1) should contain approximately 910 mug of STX equivalents per litre. Small volumes of water containing PST concentrations similar to those estimated from the cultured A. gracile would therefore contain PST amounts comparable to those used as limit enforcement for harvesting and consumption of shellfish in marine environments (80 mug of STX equivalents per 100 g of shellfish).