Cultivate Taumoeba-82.5

After the Hail Mary's catastrophic encounter with Adrian's atmosphere left the ship damaged and its crew compartment contaminated with Taumoeba, Grace and Rocky turned their attention to the central problem: the natural Taumoeba, which preyed on Astrophage, could not survive the nitrogen present in the breeding zones of Venus or Threeworld. The Astrophage breeding grounds on both planets, where the air pressure is 0.02 atmospheres, contain 3.5 percent nitrogen on Venus and 8 percent on Threeworld. The Taumoeba from Adrian died within seconds when exposed to even small amounts of elemental nitrogen, a gas harmless to both humans and Eridians. This was the obstacle that had to be overcome if the predator was to be deployed to save either world.

The Nitrogen Problem and the Breeding Strategy

Grace realized that the solution lay not in understanding why nitrogen killed Taumoeba, but in using evolution itself to overcome the barrier. He explained to Rocky that humans use antibiotics to fight diseases, but over time diseases evolve resistance. The same principle could be applied to Taumoeba: create an environment that is barely deadly, breed the survivors, then increase the nitrogen concentration and repeat the process. Rocky immediately grasped the concept, comparing it to a disease evolving a defense against the chemical that kills it. Grace asked Rocky to build ten small, identical test chambers with precise gas injection systems, allowing exact control over the nitrogen quantity in each tank. Rocky delivered, creating chambers that could control nitrogen content to within one part per million.

The Breeding Process and Gradual Progress

Grace set up ten breeder tanks, each with a different nitrogen concentration. Tank One served as the control at 0.6 percent nitrogen, the level the current generation could already handle. Tanks Two through Ten received progressively higher concentrations, from 0.65 percent up to 1.05 percent, in 0.05 percent increments. The heartiest survivors from each generation became the champions that moved on to the next round. Taumoeba has a remarkably fast doubling time, allowing Grace to observe multiple generations within hours. Over weeks of work, the nitrogen tolerance crept upward: Taumoeba-06, then Taumoeba-35, which could survive the 3.5 percent nitrogen found on Venus. Grace celebrated this milestone but insisted they push further, aiming for Taumoeba-80 to handle Threeworld's 8 percent nitrogen. Rocky, ever the engineer, kept working on his own projects while Grace monitored the tanks, but both understood the stakes.

The Unintended Consequence of Xenonite Permeability

As the generations advanced, Grace noticed something alarming. The Taumoeba-82.5 strain, which finally achieved the target nitrogen resistance, had also evolved an unexpected ability: it could work its way through xenonite. The breeder tanks were made of xenonite, and the Taumoeba had learned to hide from the nitrogen by worming into the material's molecular structure. Grace confirmed this with a controlled experiment, placing Astrophage samples sealed between xenonite discs and between plastic discs in containers with Taumoeba-82.5. The xenonite-covered Astrophage was consumed; the plastic-covered sample remained untouched. Natural Taumoeba could not penetrate xenonite at all. This meant that Rocky's ship, the Blip-A, which used xenonite for critical bulkheads and fuel tanks, was vulnerable. Grace realized with horror that the same strain he had sent with Rocky would inevitably escape its xenonite enclosures and consume the Blip-A's fuel, leaving Rocky derelict in space.

The Final Achievement and Its Consequences

Despite this devastating discovery, the breeding program itself was a complete success. Grace checked Tank Nine and found its slide clear of Astrophage, confirming that Taumoeba-80 had survived and fed. Tank Ten was also clear, indicating Taumoeba-82.5. Rocky was ecstatic, bouncing around his tunnel and demanding that Grace immediately run thorough tests with exact Venus and Threeworld atmospheres. Grace agreed, but first needed to breed up a stable colony and create sealed metal containers for storage, since xenonite was no longer safe. He built a new farm out of sheet aluminum on the CNC mill, salvaging the operational equipment from Rocky's xenonite farms. The Taumoeba-82.5 strain, stored in metal, would still do its job on Venus and Threeworld. But the unintended side effect had already set in motion the crisis that would force Grace to abandon his own return to Earth and instead turn the Hail Mary around to rescue his friend.