Metallic archaea were an artificially modified subculture of archaea created by Code Talker. It could be used to near instantly oxidize and melt any metal it is applied to. This allowed it to render weapons unusable, especially nuclear ones, with their capabilities. It could also be used to contain and consume radiation as well as radioactive materials, such as uranium. Alternatively, it could be used to make better and faster mechanisms, increasing a machine's reaction speed and allowing them to lock and release their individual joint parts at will, much like a living creature.
The Parasite Unit were equipped with metallic archea, which the Armor and Mist Unit could use to turn people to puppet soldiers. The Mist Unit could use to create a blinding gas, and all of them could use to manifest weapons from thin air while the Armor Unit could generate metallic substance from their bodies, creating bulletproof armor over their skin or infuse it into the ground to cause metallic spike like structures to erupt from the ground as a means of creating a protective wall that defended against bullets and explosions or to harm nearby enemies as a means of attack. They also had machetes with the corrosive version of metallic archaea, allowing them to burn and corrode whatever they hit. The metallic archaea found on the Skulls' machetes and in the corrosive gas clouds has a fiery orange sparkly color while the variant emitted from the Skulls and Puppet soldiers's bodies has a blue sparkly color. The Skulls were shown to have luminescent blue blood when damaged. The effects, uses and capabilities of metallic archaea could also be compared to that of nanomachines.
Code Talker first began work on the metallic archaea during the Cold War. Since the ground beneath the Navajo nation was rich with uranium ore that could be utilized in nuclear weaponry, the U.S. government set up countless mines on their land and sent the Navajo people there to work. Many were irradiated because of their close contact with uranium and became sick and died. Around this time, Code Talker discovered microbes that could "eat" uranium, and he believed he could use them to cleanse the Navajo of the irradiation. However, the research's required funding was much too high. Nobody was willing to invest in his research but Skull Face. Skull Face put Code Talker to research the microbes' potential in nuclear weaponry rather than uranium clean-up, holding the Navajo people hostage to force Code Talker to abandon his old work and move on.
In his time working under Skull Face, Code Talker created a metallic offspring of pure archaea that subsisted on metals rather than organic matter, dubbing it "metallic archaea." The uranium strain of metallic archaea were quickly used in the production of Metal Gear Sahelanthropus and other XOF projects. During this time Code Talker also created a subspecies known as corrosive archaea that could be used as a weapon on its own.
The technology spread relatively slowly, eventually landing in the hands of Huey Emmerich and assisting in the creation of his exo-legs, using more docile forms of metallic archaea to increase the exo-legs' reaction speed and enable him to lock and release his joints at will. He also was nearly on the receiving end of metallic archaea by Ocelot during an interrogation session, which had destroyed his old glasses, eventually resulting in Huey divulging the location of Metal Gear as being at OKB Zero. Ocelot then placed the syringe right at Huey's leg, forcing him to keep his leg up to prevent the plunger from injecting it into his leg (as the needle already pierced through his skin).
Uranium enrichment archaea
Uranium enrichment archaea was first discovered by Code Talker in 1973. The archaea metabolized uranium-235, producing weapons-grade enriched uranium. This process was similar to how plants fractionate carbon isotopes when conducting photosynthesis. They were placed inside of Sahelanthropus to allow it to activate a nuclear self-destruct, and they were also inactive inside the yellowcake recovered by Venom Snake in Central Africa. They were required to be stored inside of yellowcake to survive and were normally kept dormant inside, similarly to baker's yeast.
The less popular but much more dangerous corrosive archaea oxidized metals, feeding off the energy in the electrons they received from the process. This corrosive archaea was used against Venom Snake when he attempted to escape Central Africa with Code Talker in a chopper, a large cloud of them almost instantly rusting over the entire aircraft and causing it to crash at Nova Braga Airport. Certain members of the Parasite Unit also stored corrosive archaea under their parasitic skin and could release it to incapacitate machinery and vehicles, and it is implied that the Parasite Unit's signature machetes were coated in corrosive archaea to increase their sharpness exponentially.
The nuclear bombs Skull Face planned to spread around the world were equipped with a failsafe to make sure his buyers wouldn't turn the weapons on him. The detonator would be destroyed using corrosive archaea and render the nuke useless, so no detonation was possible unless Skull Face disengaged the lock.