Deinococcus–Thermus is a phylum of bacteria with a single order, Deinococci, that are highly resistant to environmental hazards, also known as extremophiles.These bacteria have thick cell walls that give them gram-positive stains, but they include a second membrane and so are closer in structure to those of gram-negative bacteria. Cavalier-Smith calls this clade Hadobacteria (from Hades, the Greek underworld).