Analyze This: These viruses are behemoths | Science News for Students

Analyze This: These viruses are behemoths

Don’t worry, though, since giant viruses target amoebas, not people
Jun 13, 2018 — 6:30 am EST
electron microscopy images of three very very large viruses

Three giant viruses are shown here (from left to right): Pacmanvirus, Mollivirus and Pandoravirus


Usually viruses are thought to be teeny tiny. After all, they invade cells. And cells are pretty tiny themselves. But viruses can vary greatly in size. Some are almost as big as bacteria. These so-called gigantor viruses carry a lot of information within what is also a relatively large amount of genetic material. Depending on the virus, those data are coded within its DNA (or its single-stranded cousin, RNA).

The good news: Humans aren’t on a gigantor’s menu. These viruses usually prey on single-celled organisms called amoebas.

To date, scientists have found around 10 potential families of mega-viruses. Many take the shape of multi-sided capsules or egglike ovals. However, there are some exceptions. Mollivirus is roughly spherical. Pacmanvirus (leftmost image, above) has an outer shell that resembles its namesake.

Two of the viruses charted here, Mimivirus and Marseillevirus, are from families confirmed to be giants. Eight others (also in blue) come from virus families that might be giants. Influenza A virus and the E. coli bacterium, both in gray, are included for comparison. The circle for each viral giant (or potential giant) also shows the year that it was first recognized. Circles for each virus are scaled and colored according to genome size (the amount of its DNA or RNA, measured in terms of its number of base pairs).
Graphic: C. Chang; Sources: P. Colson, B. La Scola and D. Raoult/Annual Review of Virology 2017; J. Andreani et al/Frontiers in Microbiology 2018

Data Dive: 

  1. What types of viruses do the diagram and text highlight?
  1. What three key pieces of information about the highlighted viruses are shown in the “Viral titans” diagram? Explain how each piece of information is displayed in the diagram. Don’t forget to include units, where appropriate.
  1. What information can be drawn by including a comparison to influenza A in the diagram?
    1. Why is the circle representing influenza A so small?
    2. According to the diagram, what is the particle length of influenza A? Roughly how many base pairs does it contain? What about for the Mimivirus
  1. What is the approximate particle length of the E. coli bacterium? According to the diagram, how big is its genome?
    1. What information can be drawn by including the comparison to the E. coli bacterium?
    2. The genome of E. coli is large. The number of base pairs runs in the millions. Can you tell from looking at the diagram what the actual number is? How well does the diagram display that type of information?
    3. Why do you think the diagram does not give base-pair information specifically for influenza A or E. coli? Would you add that information to the diagram? Explain your reasoning.

Beyond the Data:

  1. What is the overall purpose of this diagram? How could it be modified to better align with that purpose?
  2. How could you redesign this diagram to show the same data? Be creative, and sketch your new diagram.


Analyze This! explores science through data, graphs, visualizations and more. Have a comment or a suggestion for a future post? Send an email to

Power Words

(for more about Power Words, click here)

align     (noun: alignment) To place or organize things in a patterned order, following an apparent line.

amoeba     A single-celled microbe that catches food and moves about by extending fingerlike projections of a colorless material called protoplasm. Amoebas are either free-living in damp environments or they are parasites.

bacterium     (pl. bacteria) A single-celled organism. These dwell nearly everywhere on Earth, from the bottom of the sea to inside of plants and animals.

base pairs     (in genetics) Sets of nucleotides that match up with each other on DNA or RNA. For DNA, adenine (A) matches up with thymine (T), and cytosine (C) matches up with guanine (G).

behemoth     A term for anything that is amazingly big. The term comes from a monstrous animal described in the Bible’s book of Job.

DNA     (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

E. coli     (short for Escherichia coli) A common bacterium that researchers often harness to study genetics. Some naturally occurring strains of this microbe cause disease, but many others do not.

genetic     Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.

genome     The complete set of genes or genetic material in a cell or an organism. The study of this genetic inheritance housed within cells is known as genomics.

influenza     (also known as flu) A highly contagious viral infection of the respiratory passages causing fever and severe aching. It often occurs as an epidemic.

microbiology      The study of microorganisms, principally bacteria, fungi and viruses. Scientists who study microbes and the infections they can cause or ways that they can interact with their environment are known as microbiologists.

particle     A minute amount of something.

prey     (n.) Animal species eaten by others. (v.) To attack and eat another species.

range     (in math or for measurements) The extent to which variation in values is possible. Also, the distance within which something can be reached or perceived.

RNA     A molecule that helps “read” the genetic information contained in DNA. A cell’s molecular machinery reads DNA to create RNA, and then reads RNA to create proteins.

spherical     Adjective for something that is round (as a sphere).

titan     The term for any gigantic being. The term comes from Greek mythology. The six sons and six daughters of the Greek gods Uranus and Gaea were known as titans. Capitalized Titan is a moon of Saturn.

virus     Tiny infectious particles consisting of RNA or DNA surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.

Further Reading

Journal: J. Abrahão et al. Tailed giant Tupanvirus possesses the most complete translational apparatus of the known virosphereNature Communications. Published online February 27, 2018. doi: 10.1038/s41467-018-03168-1.

Journal: J. Andreani et al. Orpheovirus IHUMI-LCC2: A new virus among the giant virusesFrontiers in Microbiology. Vol. 8, January 22, 2018, p. 2643. doi: 10.3389/fmicb.2017.02643.

Journal:  P. Colson et al. Giant viruses of amoebae: A journey through innovative research and paradigm changesAnnual Review of Virology. Vol. 4, September 2017, p. 61. doi: 10.1146/annurev-virology-101416-041816.

Source Story (Science News): Meet the giants among viruses