Candidate Cyanide Resistance Genes in Eutardigrade (Tardigrada) Genomes and KCN Resistance of Hypsibius exemplaris

Several eutardigrade species can withstand high doses of potassium cyanide (KCN), a potent inhibitor of mitochondrial respiration, suggesting defense mechanisms that remain poorly understood. We surveyed the available tardigrade genomes in search for 11 protein families associated with cyanide detoxification and resistance in other organisms. We identified 28 sequences putatively encoding mitochondrial alternative oxidase (AOX), as well as proteins from the nitrilase superfamily and rhodanese superfamily in three eutardigrades, but found no evidence for other canonical cyanide-detoxifying enzymes such as β-cyanoalanine synthase. We also experimentally tested KCN resistance of the model tardigrade species Hypsibius exemplaris using a standard exposure protocol (100 mM KCN, 10 min) to determine if its poor anhydrobiotic ability reflects on its capacity for KCN resistance. All specimens survived KCN exposure, with a mean recovery time that did not differ significantly from other tardigrade species, previously tested under identical conditions, suggesting that KCN resistance may be a shared trait among eutardigrades. However, confirming whether this represents a conserved feature across the Eutardigrada class will require broader sampling. While these findings highlight potential pathways, they are limited by the lack of functional or expression validation for the identified genes.