Abstract
In August 2019, three dogs died after bathing in or drinking from Mandichosee, a mesotrophic reservoir of the River Lech (Germany). The dogs showed symptoms of neurotoxic poisoning and intoxication with cyanotoxins was considered. Surface blooms were not visible at the time of the incidents. Benthic Tychonema sp., a potential anatoxin-a (ATX)-producing cyanobacterium, was detected in mats growing on the banks, as biofilm on macrophytes and later as aggregations floating on the lake surface. The dogs’ pathological examinations showed lung and liver lesions. ATX and dihydroanatoxin-a (dhATX) were detected by LC-MS/MS in the stomachs of two dogs and reached concentrations of 563 and 1207 µg/L, respectively. Anatoxins (sum of ATX and dhATX, ATXs) concentrations in field samples from Mandichosee ranged from 0.1 µg/L in the open water to 68,000 µg/L in samples containing a large amount of mat material. Other (neuro)toxic substances were not found. A molecular approach was used to detect toxin genes by PCR and to reveal the cyanobacterial community composition by sequencing. Upstream of Mandichosee, random samples were taken from other Lech reservoirs, uncovering Tychonema and ATXs at several sampling sites. Similar recent findings emphasize the importance of focusing on the investigation of benthic toxic cyanobacteria and applying appropriate monitoring strategies in the future.
Highlights
Cyanobacteria are common components in aquatic systems
The filamentous cyanobacteria detected in mats from Mandichosee and the River Lech were identified as Tychonema due to their morphological traits [25]
The cell widths overlap with other Tychonema species, such as Tychonema bourellyi (4.0–6.0 μm) or T. tenue (5.5–8 μm), Tychonema in the River Lech is probably Tychonema bornetii due to its benthic occurrence
Summary
Cyanobacteria are common components in aquatic systems. Phototrophic cyanobacteria are ubiquitously distributed, can form mass populations under eutrophic conditions and certain strains of many taxa can produce different toxins [1,2,3,4,5]. The toxicity of cyanotoxins can be ranked between the tetrodotoxin of marine poisonous animals and strychnine from Strychnos nux-vomica, known as arrow poison [6]. According to their mode of action, cyanotoxins can be divided into hepatotoxins, neurotoxins and cytotoxins, leading to liver or respiratory failure after ingestion of hazardous amounts of toxins [6]. Effects reported after contact with cyanobacteria include, e.g., odor impairments, skin reactions and gastrointestinal problems. These are, rather attributed to other metabolites from cyanobacteria or associated bacteria than to cyanotoxins
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