Bacterial biofilms build their own plumbing and resist antibiotics a hundredfold
Prokaryotes are single cells with no nucleus, yet many team up in biofilms that behave almost like a body. Dome-shaped colonies are laced with channels that carry water and oxygen, cells signal to one another, and the whole community can be around 100 times harder to kill with antibiotics than a lone cell.
The name means before the kernel, reflecting the absence of a nucleus or other membrane-wrapped compartments. Modern classification splits prokaryotes into two domains, Bacteria and Archaea. Cells with nuclei, the eukaryotes, may actually sit inside the archaeal branch, and their mitochondria descend from prokaryotes that once lived inside other cells.
These were among Earth's first life forms. The last universal common ancestor, considered prokaryote-grade, is estimated at 4.09 to 4.33 billion years old. Most prokaryotes measure 1 to 10 micrometres, but they range from 0.2 micrometres in Mycoplasma genitalium to 750 micrometres in Thiomargarita namibiensis. Bacteria come as spheres, rods, spirals and commas, while one archaeon, Haloquadratum, is flat and square. Despite lacking organelles, they have simple skeletons built from relatives of the proteins actin and tubulin, and some carry protein-shelled compartments or gas vesicles.
They multiply by splitting in two, but they also swap genes sideways. Bacteria do it three ways: viruses accidentally ferry DNA between hosts, cells pass plasmids during conjugation, and in natural transformation a cell takes up DNA from the surrounding water, sometimes as much as a third of a chromosome. Transformation is known in at least 67 bacterial species. Among archaea, Haloferax volcanii builds bridges between cells, and Sulfolobus solfataricus clumps together when its DNA is damaged, perhaps to aid repair.
Communities can leave lasting marks. Cyanobacteria and other microbes form layered mats that can mineralise into stromatolites preserved as fossils, and myxobacteria even pass through multicellular stages. Prokaryotes break down waste and produce food at the base of ecosystems, and they drive the planet's cycles of carbon, nitrogen, phosphorus and oxygen.
Source: Prokaryote
