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Helicase

Microbe Lab

Most life on Earth is too small to see. Meet bacteria, archaea, fungi, protists and viruses: where they live, what they eat, and how they help or harm us.

Compare microorganisms across the three domains of life, plus viruses, which are not cells. See how shape, metabolism and habitat differ, and model how a bacterial population grows.

Contrast prokaryotic and eukaryotic microbes and acellular viruses by morphology, metabolism, reproduction and ecology, then explore nutrient-limited batch growth kinetics.

MicrobiologyImmunologyBiotechnology

Biosafety note

This lab explains microbes conceptually. Real work with living microorganisms, and especially with anything that can cause disease, requires trained people, proper facilities and institutional oversight. We describe pathogens only at the level of public-health fact sheets.Source: WHO, 2020Source: CDC

Explore microbes

Escherichia coli

E. coli

BacteriaProkaryoteMostly harmless, some strains cause disease

Its complete genome was published in 1997, a milestone for microbial genetics.

Shape
Rod (bacillus)
Size
About 1 µm wide and 2 µm long
Energy and food
Heterotroph that can grow with or without oxygen
Reproduction
Binary fission: one cell copies its DNA and splits in two
Where it lives
Intestines of warm-blooded animals, including people
Effect on people
Most strains are harmless gut residents; some strains cause food-borne illness.

Uses and importance

  • The first recombinant human insulin genes were expressed in E. coli
  • Recombinant plasmids were first shown to work in E. coli
  • One of the most studied organisms in molecular biology

Sources

Compare side by side

Tick Compare on up to three microbes. Viruses are not cells, which changes almost every row.

Comparison of selected microbes
FeatureEscherichia coliSaccharomyces cerevisiaeBacteriophages
GroupBacteriaFungiViruses
Cell typeProkaryoteEukaryoteNot a cell
ShapeRod (bacillus)Oval single cellHead holding the genome on a tail with fibers
SizeAbout 1 µm wide and 2 µm longA few micrometers across, larger than most bacteriaTens to a few hundred nanometers
Energy and foodHeterotroph that can grow with or without oxygenFerments sugar into alcohol and carbon dioxide when oxygen is scarceNone of its own; uses the machinery of the bacterium it infects
ReproductionBinary fission: one cell copies its DNA and splits in twoBudding: a small daughter cell grows from the parentInjects its genome into a bacterium, which then builds new phages
Where it livesIntestines of warm-blooded animals, including peopleFruit surfaces; widely used in kitchens and breweriesAnywhere bacteria live
Effect on peopleMostly harmless, some strains cause diseaseMostly beneficialMostly beneficial

Match each microbe to its home

Each habitat is used once. Microbes are adapted to very different places.

Choose a habitat for every microbe to check.

How a bacterial population grows

Change the settings to see how doubling time, a slow start and the food supply shape the classic growth curve.Source: Monod, 1949

Simplified model

Illustrative numbers in arbitrary conditions, not data for any real species, and not a laboratory procedure.
30 min

How long the population takes to double during its fastest growth.

1.5 h

Time cells spend adjusting to new conditions before dividing.

10⁹ cells/mL
10⁴ cells/mL
Population size over time in a closed container
Population rises from 10⁴ to about 1.0 × 10⁹ cells per mL. Phases: lag from hour 0, exponential from hour 1.6, stationary from hour 10.1, death from hour 15.3. Use the left and right arrow keys to read values.2.03.04.05.06.07.08.09.010.0051015202530354045Time (hours)log10 cells per mLExponentialStationaryDeath

Bacteria multiply by splitting in two, so their numbers double again and again. In a closed container they first adjust, then grow very fast, then stop when the food runs out, and finally start to die.

The curve shows four classic phases: lag (cells adjust), exponential (steady doubling, a straight line on this log scale), stationary (food runs out and growth stops) and death. Ten doublings multiply a population by about a thousand.

Growth rate depends on nutrient concentration with saturation (a Monod-type relationship). On a log scale, exponential growth is linear with slope ln 2 divided by the doubling time. Here death is modeled as a rate that rises as nutrients are exhausted.

Why resistance matters

When bacteria evolve resistance, antibiotics stop working. A 2022 analysis estimated that about 1.27 million deaths in 2019 were directly attributable to bacterial antimicrobial resistance, with the heaviest burden in low-resource settings.Source: GRAM Collaborators, 2022

Health agencies call antimicrobial resistance one of the most urgent public health problems, and track it closely.Source: CDC, 2025Source: WHO

Knowledge check

What did Carl Woese and George Fox's 1977 comparisons of ribosomal RNA reveal about methane-producing microbes?

Knowledge check

Which tiny cyanobacterium is described as presumably the most abundant photosynthetic organism on Earth?

Knowledge check

A large 2022 analysis estimated how many deaths in 2019 were directly attributable to bacterial antimicrobial resistance?

Your progress

Sources & 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.

  4. Construction of biologically functional bacterial plasmids in vitro (opens the original in a new tab)

    Cohen SN, Chang AC, Boyer HW, et al. (1973). Proceedings of the National Academy of Sciences 70:3240-3244.

    Recombinant plasmids that replicate in bacteria.

    Historical paperPrimary research

  7. Thermus 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 research

  10. Present and future global distributions of the marine Cyanobacteria Prochlorococcus and Synechococcus (opens the original in a new tab)

    Flombaum P, Gallegos JL, Gordillo RA, et al. (2013). Proceedings of the National Academy of Sciences 110:9824-9829.

    Peer-reviewedPrimary research
Show 30 more sources

  3. A programmable dual-RNA-guided DNA endonuclease in adaptive bacterial immunity (opens the original in a new tab)

    Jinek M, Chylinski K, Fonfara I, et al. (2012). Science 337:816-821.

    Showed Cas9 can be programmed with guide RNA to cut chosen DNA sequences.

    Peer-reviewedPrimary research

  5. Phylogenetic 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 research

  16. Protection afforded by sickle-cell trait against subtertian malarial infection (opens the original in a new tab)

    Allison AC (1954). British Medical Journal 1:290-294.

    Early evidence that carrying one sickle cell allele protects against severe malaria.

    Historical paperPrimary research

  27. 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 analysis