Hiding in plain sight: Characterizing a novel cyanobacterium that packs a potent punch

Cyanobacteria are one of the most studied groups of microbes on the planet. Yet, molecular tools, like 16S rRNA gene sequencing, show us uncultured lineages lurk across the cyanobacterial tree of life. Cyanobacterial blooms are a recurring threat to global fresh and marine waters and are exacerbated by anthropogenic climate change. The proliferation of toxin producing species in many of these blooms is concerning and a risk for public health. Cyanobacteria are known to produce a plethora of secondary metabolites, some of which are detrimental to humans. However, many of these compounds remain enigmatic regarding their role in the cell and environment. There is also an absence of information for the genes that encode many of these compounds. Here we isolated a cyanobacterium from a late season bloom in Siskiwit Bay in Lake Superior. A phylogenomic reconstruction using a 5.4 MB, circular genome shows the isolate belongs to a novel genus within the Nostocacea. The culture does not produce or carry any genes for common toxins. However, zebrafish embryos exposed to extracts taken from the culture either died or were malformed at varying ppb concentrations. This highlights that novel toxins are lurking within dark green matter of novel cyanobacteria.