A singleMicrocoleusspecies causes benthic cyanotoxic blooms worldwide

Abstract

AbstractRecently, proliferations of benthic cyanobacteria producing derivatives of anatoxin-a have been reported in rivers all over the world. In three river systems, in New Zealand, the USA, and Canada, a cohesive cluster ofMicrocoleusstrains was responsible for toxin production. Here, we document a similar toxigenic event that occurred at the mouth of the river Areuse in lake Neuchâtel (Switzerland) and caused the death of several dogs. Using 16S RNA-based community analysis, we show that riverine benthic communities are dominated by Oscillatoriales and especially byMicrocoleusstrains. We correlate the detection of one sequence variant with the presence of anatoxin-a derivatives and use metagenomics to assemble a complete circular genome of the strain. The strain is distinct from the ones isolated in New Zealand, the USA, and Canada, but belongs to the same species; it shares significant traits with them, in particular a relatively small genome and incomplete vitamin biosynthetic pathways. Overall, our results suggest that the major anatoxin-a-associated benthic proliferations worldwide can be traced back to a single ubiquitous species,Microcoleus anatoxicus,rather than to a diversity of cyanobacterial lineages. We recommend that this species be monitored internationally in order to help predict and mitigate similar cyanotoxic events.