What They Built

There is no geological process that fills a planet’s atmosphere with oxygen. It is a waste product, and one lineage made all of it.

The bill came first. Oxygen was corrosive to almost everything then alive, and the atmosphere spent two hundred million years flickering on and off before it stayed — which is the event the timeline corridor gives most of its width to.

Forests are what people picture. About half the carbon fixed on Earth each year is fixed by organisms too small to see, drifting in the top hundred metres of the sea.

They do it with a standing biomass a tiny fraction of the size of the world’s plants, by turning over in days rather than in decades.

Half a micrometre across, and the most abundant photosynthesising organism on the planet.

Nobody knew it existed until 1986 — three hundred and ten years after the first person looked into a drop of water and saw anything at all. It holds a title in the records hall, and its discovery is the last event in the timeline corridor.

One species, domesticated at least twice, and running in kitchens and breweries for thousands of years before anyone knew it was alive.

The genomes of industrial beer strains show what domestication does: they are grouped into a handful of family lineages, many of them unable to reproduce sexually any more, shaped by centuries of being taken from one batch and put into the next.

A cheese rind is a whole ecosystem, assembled in weeks, growing on a surface a person can hold.

Rinds sampled across ten countries turn out to be built from a modest, repeatable cast of bacteria and fungi, arriving in a consistent order — which is why cheese rinds have become a laboratory system for studying how communities assemble, and why the flavour of a mould-ripened cheese is a description of who moved in.

A raw cacao bean does not taste of chocolate. The flavour is not in the plant.

Beans are piled in heaps or boxes with their pulp and left for a week, and a succession works through them — yeasts first, then lactic acid bacteria, then acetic acid bacteria, each changing the conditions for the next. The heat and acid they generate kill the seed and set off the reactions inside it that produce the flavour precursors. Roasting finishes what they started.

Kōji. A mould grown deliberately on steamed rice or soy, in use for something like a thousand years, and named Japan’s national fungus.

Its genome is noticeably enriched in the enzymes that break starch and protein into sugars and amino acids — which is the entire trick, and it is why a cupboard’s worth of Japanese cooking descends from a single organism.

Citric acid is in the drink, the sweet, the cleaning spray and the tablet, and practically none of it comes from a lemon.

It is fermented, in vats, by a black mould found on damp bread and rotting fruit, which has been the industrial method for a century because the organism is absurdly good at it.

A mould spore lands on a plate of staphylococci in a London laboratory in 1928 and clears a halo around itself. Fleming published it the next year, in a paper that was largely ignored for a decade.

The organism itself was misidentified for the next eighty years. Fleming’s strain was called Penicillium chrysogenum until a 2011 re-examination of the original culture placed it in a different species, P. rubens — a reminder that identification is hard even when the specimen is the most famous fungus on Earth, and the reason nothing in the portrait hall is named until somebody competent has looked.

Streptomycin, tetracycline, erythromycin, vancomycin, chloramphenicol, rifamycin. Almost the entire clinical repertoire was found by digging up soil bacteria and asking what they secrete.

They are not making medicine. They are filamentous organisms living in the most crowded habitat on the planet, and these compounds are how they hold territory against their neighbours. That smell after rain is one of theirs too.

Akira Endo screened over six thousand fungal broths on the reasoning that some mould, somewhere, would be attacking the cholesterol pathway of its competitors.

The 1976 paper describes what he found in a Penicillium isolated from Kyoto rice. Every statin in every pharmacy descends from that molecule, and it is now among the most prescribed classes of drug in the world.

Before 1982 insulin was extracted from the pancreases of slaughtered pigs and cattle, at roughly a tonne of pancreas for a hundred grams of hormone.

The 1979 paper reports the two chains of human insulin, chemically synthesised as genes and expressed in a gut bacterium. It became the first recombinant medicine approved anywhere, and the supply of insulin stopped depending on the supply of livestock.

Thomas Brock pulled a pink bacterium out of a hot spring in Yellowstone in the 1960s, at a temperature where nothing was supposed to grow, and deposited it in a culture collection because it was interesting.

Copying DNA means heating it until the strands come apart, which destroys the enzyme doing the copying. This organism’s enzyme survives the heat, because it evolved at 70 °C. That is the whole of PCR: paternity tests, forensic evidence, ancient DNA, every diagnostic swab, all of it running on a heat-tolerant protein from a spring nobody was farming for products.

The bacterium that acidifies yogurt and mozzarella has one industrial problem: the viruses that infect it can ruin a whole vat.

Researchers at a dairy-culture company noticed that surviving strains had captured fragments of the attacker’s DNA into a strange repeated region of their own genome, and were using it to recognise the virus next time. The 2007 paper demonstrating that is where CRISPR stops being a curiosity in a database and becomes an immune system — and, a few years later, a way to edit any genome you like.

It is a bacterial defence, four billion years old, found in a starter culture.

An mRNA vaccine is a transcript, made in a tank rather than in a cell, and the enzyme doing the transcribing belongs to a virus that infects E. coli.

T7’s polymerase is fast, it is fussy about which promoter it starts from, and it needs nothing else present to work — which is exactly what you want in a vat. The 1986 paper that put it to work as an expression system is one of the most used methods in biology.

The virus is not in the vaccine. Its transcription machinery is what makes the vaccine possible.

Soil is not dirt with things living in it. It is a structure that microorganisms build and hold together, and it is where the carbon and nitrogen a plant needs are released from what died last season.

A global survey of soils across six continents found the same small set of bacterial types dominating almost everywhere — a few hundred out of an unimaginably larger pool, running most of the process, in deserts, forests and farmland alike.

Somewhere around two billion years ago a bacterium ended up inside another cell and was not digested. Its descendants are in every cell of your body, and they still carry their own genome, which is still recognisably bacterial.

Every breath you take is oxygen going to them.

This is the last credit and it is the one that matters: the visitor is not the audience for this exhibit so much as another thing on the list of what these organisms have built. The timeline corridor puts the event two billion years back.