Enzyme 42

Enzyme 42 is the only known cure for the Kharaa Bacterium in the Subnautica franchise. It is naturally produced by the Sea Emperor Leviathan and was the key to curing the planet-wide infection on Planet 4546B. The enzyme is named for being the 42nd compound studied by the Architects during their centuries-long search for a Kharaa cure.

Discovery

The Architects identified Enzyme 42 as a potential Kharaa cure after discovering that the Sea Emperor Leviathan was naturally immune to the bacterium. They captured the Sea Emperor, the last of its species, and imprisoned it in the Primary Containment Facility at approximately 1,200 meters depth in the Lava Lakes biome. Their goal was to extract and synthesize Enzyme 42 at a scale sufficient to cure their civilization.

The problem

The captive Sea Emperor was approximately 2,600 years old, far exceeding its species' natural lifespan. Its extreme age caused the enzyme it produced to be unstable and insufficient for large-scale use. The Architects could not synthesize a stable version from the adult's degraded output. They held five unhatched Sea Emperor eggs in the facility, hoping the juveniles would produce viable enzyme, but the eggs would not hatch in captivity.

The Sea Emperor communicated telepathically with Ryley Robinson, the first being to hear its voice. The Architects could not perceive its telepathy. The Emperor asked Ryley for help: hatch its eggs so that its young could be free.

The hatching

Ryley crafted hatching enzymes using five ingredients gathered from across the planet through the Primary Containment Facility's Alien Arch teleporters:

The cure

All five eggs hatched. The juvenile Sea Emperors, approximately 90 meters long, produced stable Enzyme 42 immediately. They released massive quantities into the water, curing every infected organism in the ocean, including Ryley. The enzyme appeared as small orange floating globules that cured on contact.

The juveniles departed through an Alien Arch connected to the Quarantine Enforcement Platform, heading out into the planet's open ocean. Shortly after, the adult Sea Emperor played with its offspring briefly before dying of old age, releasing the last of its enzyme as it passed.

In Below Zero

Despite the planet-wide cure, the Kharaa Bacterium persisted in at least one location: a Frozen Leviathan in the Glacial Basin, preserved by extreme cold. Alterra Corporation discovered the infected specimen and began studying the pathogen for potential weaponization. Robin Ayou ultimately neutralized it using an antidote crafted from Frost Vase Plant and Fevered Pepper, which functioned similarly to Enzyme 42.

Connection to Subnautica 2

Whether Enzyme 42 or a similar cure exists for the Blight on Planet Zezura is unknown. The Blight appears to be a distinct organism from the Kharaa Bacterium, and the biological systems of Zezura may require entirely different solutions. The Biosampler and DNA Adaptation System suggest that Subnautica 2 takes a different approach to the player's relationship with alien biology, with the protagonist modifying their own DNA rather than seeking a single cure for an infection.