Discovery of a novel microcystin-producing Snowella (Chroococcales, Cyanobacteria) from the Qinghai-Tibet Plateau: expanding the diversity of cyanotoxin source origins in aquatic ecosystems.

Cyanobacteria-derived microcystins (MC) are widespread hepatotoxins threatening water security, with known producers primarily limited to specific genera. To expand the diversity of MC-producing cyanobacteria, we conducted an environmental DNA (eDNA)-based survey of cyanobacterial communities across the Lake Qinghai Basin (Qinghai-Tibet Plateau), a unique high-altitude brackish aquatic system, and isolated six coccoid cyanobacterial strains from Lake Yueya, a shallow sub-lake of Lake Qinghai. These six strains were characterized via a polyphasic approach, and morphological examinations (light and transmission electron microscopy) revealed key diagnostic features of Snowella (Chroococcales, Cyanobacteria), including spherical colonies with radial cell arrangements and central stalks. Further, molecular analyses confirmed their affiliation with Snowella via 16S rRNA gene and 16S-23S ITS phylogeny, and the MC synthesis gene mcyE was successfully detected. UPLC-MS/MS further identified MC variants (MC-LR, MC-RR, MC-YR) in selected strains, and strain CHAB 6606 was detected to have intracellular MC-LR (82.4 fg·cell⁻¹) and MC-YR (247.0 fg·cell⁻¹), higher than the typical Microcystis strains. Notably, our deposited mcyE sequences in Genbank are the sole basis for identifying the three global locations with potential MC-producing Snowella populations. This study provides the first formal confirmation that Snowella produces MC, expanding the diversity of MC-producing cyanobacteria to high-altitude brackish habitats. Our findings establish a molecular framework for global Snowella-associated MC risk surveillance, supporting targeted aquatic toxin monitoring and advance understanding of the taxonomic spectrum of MC-producing cyanobacteria worldwide.