Our bacterium boasts strong, highly sophisticated electrochemical pumps working through specialized fauceted porins that can slurp up and spew out just the proper mix of materials. When it's running its osmotic pumps in some nutritious broth of tasty filth, our tank car can pump enough juice to double in size in a mere twenty minutes. And there's more: because in that same twenty minutes, our bacterial tank car can build in entire duplicate tank car from scratch.
Inside the outer wall of protective bark is a greasy space full of chemically reactive goo. It's the periplasm. Periplasm is a treacherous mess of bonding proteins and digestive enzymes, which can yank tasty fragments of gunk right through the exterior hide, and break them up for further assimilation, rather like chemical teeth. The periplasm also features chemoreceptors, the bacterial equivalent of nostrils or taste- buds.
Beneath the periplasmic goo is the interior cell membrane, a tender and very lively place full of elaborate chemical scaffolding, where pump and assembly-work goes on.
Inside the interior membrane is the cytoplasm, a rich ointment of salts, sugars, vitamins, proteins, and fats, the tank car's refinery treasure-house.
If our bacterium is lucky, it has some handy plasmids in its custody. A plasmid is an alien DNA ring, a kind of fly-by-night genetic franchise which sets up work in the midst of somebody else's sheltering cytoplasm. If the bacterium is unlucky, it's afflicted with a bacteriophage, a virus with the modus operandi of a plasmid but its own predatory agenda.
And the bacterium has its own native genetic material. Eukaryotic cells -- we humans are made from eukaryotic cells -- possess a neatly defined nucleus of DNA, firmly coated in a membrane shell. But bacteria are prokaryotic cells, the oldest known form of life, and they have an attitude toward their DNA that is, by our standards, shockingly promiscuous. Bacterial DNA simply sprawls out amid the cytoplasmic goo like a circular double-helix of snarled and knotted Slinkies.
Any plasmid or transposon wandering by with a pair of genetic shears and a zipper is welcome to snip some data off or zip some data in, and if the mutation doesn't work, well, that's just life. A bacterium usually has 200,000 or so clone bacterial sisters around within the space of a pencil dot, who are more than willing to take up the slack from any failed experiment in genetic recombination. When you can clone yourself every twenty minutes, shattering the expected laws of Darwinian heredity merely adds spice to life.
Bacteria live anywhere damp. In water. In mud. In the air, as spores and on dust specks. In melting snow, in boiling volcanic springs. In the soil, in fantastic numbers. All over this planet's ecosystem, any liquid with organic matter, or any solid foodstuff with a trace of damp in it, anything not salted, mummified, pickled, poisoned, scorching hot or frozen solid, will swarm with bacteria if exposed to air. Unprotected food always spoils if it's left in the open. That's such a truism of our lives that it may seem like a law of physics, something like gravity or entropy; but it's no such thing, it's the relentless entrepreneurism of invisible organisms, who don't have our best interests at heart.
Bacteria live on and inside human beings. They always have; bacteria were already living on us long, long before our species became human. They creep onto us in the first instants in which we are held to our mother's breast. They live on us, and especially inside us, for as long as we live. And when we die, then other bacteria do their living best to recycle us.
An adult human being carries about a solid pound of commensal bacteria in his or her body; about a hundred trillion of them. Humans have a whole garden of specialized human-dwelling bacteria -- tank-car E. coli, balloon-shaped staphylococcus, streptococcus, corynebacteria, micrococcus, and so on. Normally, these lurkers do us little harm. On the contrary, our normal human-dwelling bacteria run a kind of protection racket, monopolizing the available nutrients and muscling out other rival bacteria that might want to flourish at our expense in a ruder way.
But bacteria, even the bacteria that flourish inside us all our lives, are not our friends. Bacteria are creatures of an order vastly different from our own, a world far, far older than the world of multicellular mammals. Bacteria are vast in numbers, and small, and fetid, and profoundly unsympathetic.
So our tank car is whipping through its native ooze, shuddering from the jerky molecular impacts of Brownian motion, hunting for a chemotactic trail to some richer and filthier hunting ground, and periodically peeling off copies of itself. It's an enormously fast-paced and frenetic existence. Bacteria spend most of their time starving, because if they are well fed, then they double in number every twenty minutes, and this practice usually ensures a return to starvation in pretty short order. There are not a lot of frills in the existence of bacteria. Bacteria are extremely focussed on the job at hand. Bacteria make ants look like slackers.
And so it went in the peculiar world of our acquaintance the tank car, a world both primitive and highly sophisticated, both frenetic and utterly primeval. Until an astonishing miracle occurred. The miracle of "miracle drugs," antibiotics.
Sir Alexander Fleming discovered penicillin in 1928, and the power of the sulfonamides was recognized by drug company researchers in 1935, but antibiotics first came into general medical use in the 1940s and 50s. The effects on the hidden world of bacteria were catastrophic. Bacteria which had spent many contented millennia decimating the human race were suddenly and swiftly decimated in return. The entire structure of human mortality shifted radically, in a terrific attack on bacteria from the world of organized intelligence.
At the beginning of this century, back in the pre-antibiotic year of 1900, four of the top ten leading causes of death in the United States were bacterial. The most prominent were tuberculosis ("the white plague," *Mycobacterium tuberculosis*) and pneumonia (*Streptococcus pneumoniae,* *Pneumococcus*). The death rate in 1900 from gastroenteritis (*Escherichia coli,* various *Campylobacter* species, etc.) was higher than that for heart disease. The nation's number ten cause of death was diphtheria (*Corynebacterium diphtheriae*). Bringing up the bacterial van were gonorrhea, meningitis, septicemia, dysentery, typhoid fever, whooping cough, and many more.
At the end of the century, all of these festering bacterial afflictions (except pneumonia) had vanished from the top ten. They'd been replaced by heart disease, cancer, stroke, and even relative luxuries of postindustrial mortality, such as accidents, homicide and suicide. All thanks to the miracle of antibiotics.
Penicillin in particular was a chemical superweapon of devastating power. In the early heyday of penicillin, the merest trace of this substance entering a cell would make the hapless bacterium literally burst. This effect is known as "lysing."
Penicillin makes bacteria lyse because of a chemical structure called "beta-lactam." Beta-lactam is a four-membered cyclic amide ring, a molecular ring which bears a fatal resemblance to the chemical mechanisms a bacterium uses to build its cell wall.
Bacterial cell walls are mostly made from peptidoglycan, a plastic- like molecule chained together to form a tough, resilient network. A bacterium is almost always growing, repairing damage, or reproducing, so there are almost always raw spots in its cell wall that require construction work.
It's a sophisticated process. First, fragments of not-yet-peptided glycan are assembled inside the cytoplasm. Then the glycan chunks are hauled out to the cell wall by a chemical scaffolding of lipid carrier molecules, and they are fitted in place. Lastly, the peptidoglycan is busily knitted together by catalyzing enzymes and set to cure.