The tardigrade Ramazzottius varieornatus as a model of extremotolerant animals

I report the successful culture of the tardigrade Ramazzottius varieornatus by supplying the green alga Chlorella vulgaris as a food. A standard strain named YOKOZUNA-1 has been isolated from single egg of R. varieornatus. The reared animals have anhydrobiotic ability throughout their life cycle in eggs, juveniles, and adults. Body water content of adult R. varieornatus drops from 78.6% wt./wt. in hydrated state to 2.5% wt./wt. in anhydrobiotic state. Reared adults, while in an anhydrobiotic state, are tolerant of exposure to 100°C, 1 GPa, 99.8% acetonitrile, and 5000 Gy of 4He ions. Furthermore, hydrated active adults survive freezing at -2 to -20°C at a cooling rate of 1°C/min. Based on useful culture systems and extraordinary tolerance to extreme environmental conditions of R. varieornatus, this species is expected to be a suitable model for extremophile research focusing on multicellular organisms.