Joan Slonczewski: Microbe

“It could be,” Quantum said slowly. “There are many ways to make a DNA triple helix. One found in human regulatory genes alternates A-T-T triplets with G-C-C.”

“Then it has a two-letter code, not four.” Double-helical DNA has four possible pairs, since A-T is distinguished from T-A; likewise G-C differs from C-G.

Quantum added, “The triple helix is most stable in acid, just what we found in these cells.”

“Just hurry up and design some triplet analogues.” Quantum’s sentient brain could do this far faster than any human. “Triple helix,” Andra repeated. “It would resist ultraviolet damage much better, with the planet’s thin ozone layer. But how to encode proteins, with only two ‘letters’?” The triple helix had only two possible triplets; its three-letter “words” could only specify eight amino acids to build protein. “Maybe it uses words of four letters. With two possible triplets at each position, that would encode two to the fourth power, that is, sixteen possible amino acids.”

“Fifteen,” corrected Quantum, “if one is a stop signal.”

The next day, after an exhaustive medical workout, Andra felt as if a vacuum cleaner had gone through her lungs. Pelt still had a long way to recover, but at least the pesky microbes were cleaned out.

“It’s hopeless,” complained Skyhook’s eyespeaker. “If even sentients aren’t safe, we’ll never explore that planet.”

“Don’t worry,” said Quantum’s voice above the holostage. “Pelt’s nanoplast has an exceptionally high organic content. A slight redesign will eliminate the problem. Machines have that advantage.”

Still, Pelt had nearly died, thought Andra.

“Your phycoid and zooid samples all have toroid cells, too,” Quantum added. “They have circular chromosomes, with no nuclear membranes: They’re all prokaryotes. Just wait till the Free Fold hears about this,” Quantum added excitedly. “I’ve got the perfect name for the planet.”

Andra looked up. “Planet of the Bagels?”

“Planet Prokaryon.”

Prokaryon—yes, thought Andra, it sounded just pompous enough that the Fold would buy it.

Still, she thought uneasily about those regular garden rows of phycoid forest and fields, with all kinds of creatures yet to be discovered. “I wonder,” she mused. “Someone else just might have named it first.”