Organism or group
Bacteria
Small single-celled organisms without a nucleus, found almost everywhere on Earth. Most bacteria in the human body are harmless, and some are helpful.
Microbiology
Bacteria, archaea, fungi, protists and viruses.
Microbiology is the study of living things too small to see without a microscope, like bacteria, and of viruses.
Microbiologists study how microbes live, grow and evolve, their roles in health, disease and the environment, and how people use them in food, medicine and industry.
The field spans microbial physiology and diversity across the three domains of life, the human microbiome, pathogens and antimicrobial resistance, and microbes as tools in biotechnology.
Big questions
- How many kinds of microbes are there?
- How do bacteria become resistant to antibiotics?
- What do the microbes living on us do?
Key ideas
Open any idea in the knowledge graph to see what it connects to, here and in other fields.
Organism or group
Archaea
Single-celled organisms without a nucleus that form a separate domain of life from bacteria.
Organism or group
Virus
Nucleic acid in a protein coat. A virus cannot copy itself alone: it must infect a cell and use the cell's machinery.
Idea or model
Three domains of life
Comparing ribosomal RNA divides life into three domains: Bacteria, Archaea and Eukarya.
Idea or model
Microbiome
The communities of microbes living in and on a body. A 2016 estimate put a reference adult's bacteria at about 38 trillion, similar to the number of human cells.
Technology or method
Antibiotics
Drugs that kill bacteria or stop their growth. Penicillin traces back to Fleming's 1929 report of a mold that stopped bacteria growing.
Process
Antimicrobial resistance
Microbes evolving to survive drugs meant to kill them. Bacterial resistance was associated with an estimated 4.95 million deaths in 2019.
Process
Bacterial growth
In a closed culture, bacteria pass through lag, exponential, stationary and death phases.
Organism or group
Thermophiles
Microbes that thrive in heat, such as Thermus aquaticus from hot springs, the source of a heat-stable enzyme used in PCR.
Process
Nitrogen fixation
Some bacteria turn nitrogen gas into forms plants can use. Legumes house them in root nodules.
Technology or method
Phage therapy
Treating bacterial infections with viruses that infect bacteria, an approach being studied again as drug resistance grows.
Emerging researchOpen in Microbe Lab
Explore it in the labs
Interactive explorer
Compare bacteria, archaea, fungi, protists and viruses side by side, and model how a bacterial culture grows.
- Microbiology
- Evolution
- Immunology
Timeline and explorer
A sourced timeline from the double helix to CRISPR therapies, eight technologies labeled established or emerging, and a PCR model.
- Biotechnology
- Synthetic Biology
- Genetics
Current research
Search published papers and preprints in Microbiology, with clear labels for reviews, primary research, clinical trials and preprints.
Search papers in MicrobiologySources & further reading
The explanations on this page are our own summaries of these sources. Follow a link to read the original; if anything here disagrees with it, the original wins. How we choose and check sources.
Microbiology (opens the original in a new tab)
OpenStax (2016). OpenStax, Rice University.
TextbookEducationalLicence: CC BY-NC-SA 4.0 (linked, not reused)
Medical Microbiology (4th edition) (opens the original in a new tab)
Baron S (editor) (1996). University of Texas Medical Branch at Galveston.
Free to read on NCBI Bookshelf. Older edition; check newer sources for current treatment information.
TextbookEducationalTowards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya (opens the original in a new tab)
Woese CR, Kandler O, Wheelis ML (1990). Proceedings of the National Academy of Sciences 87:4576-4579.
Peer-reviewedPerspectiveAntimicrobial resistance (fact sheet) (opens the original in a new tab)
World Health Organization. who.int. World Health Organization.
Fact sheetIntergovernmental sourceBacteria (opens the original in a new tab)
National Human Genome Research Institute. Talking Glossary of Genomic and Genetic Terms. National Human Genome Research Institute, NIH.
ReferenceGovernment sourceEducationalPhylogenetic structure of the prokaryotic domain: the primary kingdoms (opens the original in a new tab)
Woese CR, Fox GE (1977). Proceedings of the National Academy of Sciences 74:5088-5090.
Ribosomal RNA comparisons revealed the archaea as a separate lineage.
Peer-reviewedPrimary researchVirus (opens the original in a new tab)
National Human Genome Research Institute. Talking Glossary of Genomic and Genetic Terms. National Human Genome Research Institute, NIH.
ReferenceGovernment sourceEducationalExpression of animal virus genomes (opens the original in a new tab)
Baltimore D (1971). Bacteriological Reviews 35:235-241.
Classified viruses by how their genomes produce mRNA.
Historical paperReviewRevised estimates for the number of human and bacteria cells in the body (opens the original in a new tab)
Sender R, Fuchs S, Milo R (2016). PLOS Biology 14:e1002533.
About 3.0 × 10^13 human cells and 3.8 × 10^13 bacteria in a 70 kg reference adult.
Peer-reviewedPrimary researchStructure, function and diversity of the healthy human microbiome (opens the original in a new tab)
Human Microbiome Project Consortium (2012). Nature 486:207-214.
Peer-reviewedPrimary researchHuman Microbiome Project (HMP) (opens the original in a new tab)
NIH Common Fund. commonfund.nih.gov. National Institutes of Health.
ReferenceGovernment sourceEducationalOn the antibacterial action of cultures of a penicillium, with special reference to their use in the isolation of B. influenzae (opens the original in a new tab)
Fleming A (1929). British Journal of Experimental Pathology 10:226-236.
The original report of penicillin's antibacterial activity.
Historical paperPrimary research
Show 8 more sourcesHide 8 sources
Global burden of bacterial antimicrobial resistance in 2019: a systematic analysis (opens the original in a new tab)
Antimicrobial Resistance Collaborators (2022). The Lancet 399:629-655.
Modelled estimate: 1.27 million deaths directly attributable to bacterial AMR in 2019.
Peer-reviewedSystematic analysisAbout Antimicrobial Resistance (opens the original in a new tab)
Centers for Disease Control and Prevention (2025). cdc.gov. U.S. Centers for Disease Control and Prevention. Published 2025-01-31.
Fact sheetGovernment sourceThe growth of bacterial cultures (opens the original in a new tab)
Monod J (1949). Annual Review of Microbiology 3:371-394.
Described bacterial growth phases and the saturating dependence of growth rate on nutrient concentration.
Historical paperReviewThermus aquaticus gen. n. and sp. n., a nonsporulating extreme thermophile (opens the original in a new tab)
Brock TD, Freeze H (1969). Journal of Bacteriology 98:289-297.
Isolation of the hot-spring bacterium later used as the source of Taq polymerase.
Historical paperPrimary researchDeoxyribonucleic acid polymerase from the extreme thermophile Thermus aquaticus (opens the original in a new tab)
Chien A, Edgar DB, Trela JM (1976). Journal of Bacteriology 127:1550-1557.
Peer-reviewedPrimary researchPrimer-directed enzymatic amplification of DNA with a thermostable DNA polymerase (opens the original in a new tab)
Saiki RK, Gelfand DH, Stoffel S, et al. (1988). Science 239:487-491.
PCR with heat-stable Taq polymerase.
Peer-reviewedPrimary researchThe rules of engagement in the legume-rhizobial symbiosis (opens the original in a new tab)
Oldroyd GE, Murray JD, Poole PS, et al. (2011). Annual Review of Genetics 45:119-144.
Editorially reviewedReviewPhage therapy: from biological mechanisms to future directions (opens the original in a new tab)
Strathdee SA, Hatfull GF, Mutalik VK, et al. (2023). Cell 186:17-31.
Peer-reviewedReview