Metallic archaea

Metallic archaea are an artificially modified subculture of archaea created by Code Talker.

History
Code Talker first began work on the metallic archaea during the Cold War. Since the ground beneath the Navajo nation were rich with uranium ore that could be utilized in nuclear weaponry, the US 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. No body 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 production of the ST-84 Metal Gear 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.

Uranium enrichment archaea
The uranium enrichment 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.

Corrosive archaea
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.

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.