No nucleus
Transcription and translation happen in one compartment, so gene control is fast and crowded.
Identity starts with a negative: no nucleus, no mitochondria. A typical cell is a few micrometres of cytoplasm, ribosomes and a tightly packed nucleoid.
Shapes ? rods, spheres, spirals, filaments ? are teaching labels. Ecology and metabolism tell you more than silhouette.
Traits
Peptidoglycan
A mesh of sugars and peptides. Beta-lactams target its construction in many pathogens.
Circular chromosome
Usually one main circle plus optional plasmids that can carry resistance or extra metabolism.
16S rRNA
A slow-changing gene used to place unknown cells on the tree without growing them.
Binary fission
One cell becomes two. Sexual meiosis is absent; diversity arrives by mutation and gene transfer.
Metabolic range
From oxygen photosynthesis to eating rock chemistry ? unmatched among familiar life.
Once you see bacteria as a domain, 'germ' becomes a thin slice of a much older story.
Keep exploring
More in Tree of microbes
Viruses
Packets of DNA or RNA that are not cells — they replicate only inside living hosts.
Familiarity 96Fungi
A eukaryotic kingdom of yeasts, moulds and mushrooms — chitin walls, external digestion, partners of plants.
Familiarity 80Archaea
A prokaryotic domain that is not bacteria — methanogens, extremophiles and no known human pathogens.
Familiarity 35Bacteriophages
Viruses that infect bacteria — Earth's most abundant biological entities, and a concept-level idea in medicine.
Familiarity 42Protozoa
Motile unicellular eukaryotes — a teaching grade that includes pond ciliates and a minority of serious parasites.
Familiarity 58