Bacterium

A bacterium is a single-celled microorganism whose DNA is not enclosed in a membrane-bound nucleus. Bacteria have diverse shapes and metabolisms, and many live in close association with other organisms.

Prokaryote: An organism whose cells lack a membrane-bound nucleus and other membrane-bound organelles. Bacteria belong to this broad cellular group, alongside archaea.
Bacterial growth: An increase in bacterial cell number through reproduction, commonly measured over time. Growth depends on conditions such as nutrients, temperature, and acidity.
Human microbiome: The communities of microorganisms and their genes associated with the human body. Bacteria make up much of these communities and affect host physiology.
Archaeon: A single-celled prokaryote belonging to the domain Archaea, distinct from bacteria. Archaea also lack nuclei but differ from bacteria in genetics and cell chemistry.
Cell membrane: A selectively permeable boundary that separates a cell from its surroundings. It controls what enters and leaves a bacterium.
Bacterial conjugation: The transfer of DNA between bacterial cells through direct contact, often involving a plasmid. It allows some traits to spread without cell division.
Pathogenic bacteria: Bacteria capable of causing disease in a host. Some bacterial species cause infections, while many others do not.
Eukaryote: An organism whose cells contain a membrane-bound nucleus and other membrane-bound compartments. Eukaryotic cells have a nucleus, unlike bacterial cells.
Bacterial cell wall: A rigid layer outside the cell membrane that gives most bacteria shape and protection. Its peptidoglycan structure distinguishes many bacteria from other cells.
Transformation (genetics): The uptake and incorporation of free DNA from a cell's surroundings. Bacteria can acquire genes released by other cells.

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