 They are resistant to cold and heat, a wide range of pH, and non-ionic detergents (Nonidet P-40 and Triton X-100).SpV1 buoyant densities are 1.39 g/cm3 in CsCl and 1.21 g/cm3 in metrizamide.Spiroplasma phages affect members of the genus "Spiroplasma", which are part of the class Mollicutes, a group of small bacteria without cell walls.