The alien bacterium is the single most dangerous biological substance on Earth after Judgement Day, and the single hardest to keep alive. In pure form it is a collection of organisms older than the planet, smarter than any terrestrial bacterium, and bound to a shared intelligence that moves them like a fleet. On its own the bacterium decays quickly in open air — it cannot survive full-strength in Earth's atmosphere for long, so it drops into a docile state to wait out its dose. That docile cycle is why C2 could feel like life returned to normal between surges. It did. The bacterium was asleep.
The delivery methods ¶
Injected, via bio-gun projectile, a dense dose punches through skin and bleeds into the organs like a normal round. The force of impact decapitates the bacterium on contact with the organs, killing both the weapon and the target — a clean balanced kill. Sprayed or airborne, the bacterium lands inside the target alive and settles into the host's system without the kill-on-impact trigger. That is where the hallucinations begin. The bacterium, collectively, can push an image into a host's perception. Many hosts at once share the same vision. A single commander somewhere upstream is running the whole thing as a hive mind.
The scale problem ¶
Producing enough bacterium to break a major city is not trivial. The aliens have cloning pipelines that the Grids never matched, but even those pipelines take years to build a Judgement-Day-sized stockpile. The event that dropped the Bacterium Zones onto the map was the result of a slow, patient accumulation the aliens had been working on since before the Grids noticed. It is rare and difficult to do at scale — which is why the Grids do not see global-scale bacterium events every year, only the one planned one, and why the Northern Dominion's parasite programme runs at a ~1.5 % success rate without ever stockpiling enough bacterium to do a regional event on its own.
The docile phase ¶
Bacterium can go dormant. That is the pattern of infection. It surges. It rests. It surges again. The rest phases are not recovery — they are the bacterium choosing not to burn itself out before the next pulse. Which means any region that looks "clean" post-infection is probably not clean. It is waiting. The Ghost Hunters built a whole faction around understanding that cycle, because the cold north is where the bacterium is most likely to be waiting the longest.
Why it matters ¶
The bacterium is the ticking clock underneath the entire C1 arc. The On-Grid does not fear the Off-Grid's raiders. It fears the species that, without ever landing, can manufacture a quiet dose of bacterium on its own clock and drop it wherever the aliens decide. Everything the network does — e-hair, the Grid domes, the secret labs — is a response to the fact that the next Judgement Day is not an if.