Extreme Habitats — prokaryotes are everywhere
Prokaryotes are ubiquitous: hot springs, Antarctic ice, deep under pressure, inside you. They are extremely resilient and metabolically flexible — they capture and recycle carbon and nitrogen, form soil, and even feed climate change. Click any glowing point to explore, or take the tour.
Symbiosis Scale — from cooperation to opposition
Any interaction between different species living together in a community is called symbiosis. These interactions fall along a continuum between opposition and cooperation, and may help, harm, or not affect each partner. (The categories are not always distinct — S. epidermidis on our skin could be called commensalism or mutualism.) Pick a type of relationship and read the scale.
Microbiome Map — the prokaryotes on and inside you
The microbiome is all prokaryotic and eukaryotic microorganisms and their genetic material associated with a certain organism. It contains resident microbiota (always present) and transient microbiota (temporary — sometimes pathogens). Explore the body sites below — then press Give antibiotics and watch what happens to the vaginal environment when the resident defenders disappear.
Proteobacteria ID Lab — five classes, many pathogens
In 1987 Carl Woese proposed the “purple bacteria and their relatives” as one phylum of gram-negative bacteria based on genome sequences — they became the Proteobacteria, divided into five classes. Browse the classes, then take the case challenge: diagnose each case file and name the class.
Gram-Positive Gallery — high G+C vs low G+C
Gram-positive prokaryotes have a multiple-layer peptidoglycan wall that retains crystal violet (they appear purple). Modern classification also uses G+C content and 16S rRNA: Actinobacteria = high G+C (>50%), Bacilli = low G+C (<50%). Click each genus to read its file — and don't miss Why acid-fast?
Phototrophs — pigments, sulfur and oxygen
Phototrophic bacteria are not a taxon — they are any bacteria using sunlight as their primary energy source. They split into oxygenic photosynthesis (makes O2) and anoxygenic (doesn’t) — and with the exception of most cyanobacteria, they are anoxygenic. Pick a group.
Archaea — the third domain
Archaea are all unicellular, but differ from bacteria in important ways: membranes use ether linkages with branched isoprene chains (bacteria: ester linkages, unbranched fatty acids); walls lack peptidoglycan (some have pseudopeptidoglycan/pseudomurein); and their genomes are larger and more complex. Five major phyla are recognized: Crenarchaeota, Euryarchaeota, Korarchaeota, Nanoarchaeota, Thaumarchaeota. With few exceptions they are not human pathogens.
Chapter Quiz — Prokaryotic Diversity
Twenty-five questions covering the whole chapter: habitats and symbiosis, the microbiome, the five classes of Proteobacteria, nonproteobacteria, phototrophs, gram-positives and archaea.