Unanticipated similarities and expected differences in the taxonomic composition and potential toxicity of cyanobacteria in biological soil crusts across hot and cold deserts.

The hot deserts of California and the cool, mountainous deserts of the Eastern Pamir region are geographically and climatically distinct, yet they share a common feature. Their arid soils host pioneering microorganisms that form biological soil crusts (BSCs), one of the earliest forms of life in this biome. This study aimed to reveal and compare the taxonomic composition, structure, and potential toxicity of cyanobacteria in these distant deserts, using simultaneous analysis. We observed significant differences in soil chemical properties, with higher average electrical conductivity in California and higher median levels of iron, nitrogen, carbon, magnesium, sodium, potassium, and calcium in Pamir. Despite this, the taxonomic composition and structure of the core bacteria phyla were similar, with Pseudomonadota, Actinomycetota, Bacteroidota, and Cyanobacteriota dominating in both locations. However, at the family level, bacterial communities showed more variability. Within Cyanobacteriota, the most abundant groups in California's biocrust samples were unidentified families, followed by Nostocaceae, Coleofasciculaceae, Chroococcidiopsidaceae, and Phormidiaceae. In Pamir, Nodosilineaceae and Nostocaceae dominated, with a lower contribution from unknown families. In samples from both deserts, we identified cyanobacterial species known to produce cyanotoxins, along with the genes