List the 3 basic forms of bacteria. List and define 5 various arrangements of cocci. Define and offer the abbreviation for the metric unit of length termed micrometer and state the average size of a coccus-shaped bacterium and also a rod-shaped bacterium. List and also explain 2 various arrangements of bacilli. List and define 3 different spiral creates of bacteria.

Bacteria are prokaryotic, single-celled, microscopic organisms (Exceptions have been discovered that have the right to reach sizes simply visible to the naked eye. They incorporate Epulopiscium fishelsoni, a bacillus-shaped bacterium that is generally 80 micrometers (µm) in diameter and 200-600 µm long, and also Thiomargarita namibiensis, a spherical bacterium in between 100 and also 750 µm in diameter.)

incredibly complicated despite their tiny size. Even though bacteria are single-celled organisms, they are able to connect via one an additional through a procedure called quorum sensing. In this method they have the right to function as a multicellular population quite than as individual bacteria. This will be discussed in higher detail in Unit 2.

For More Information: Bacterial Communication via Quorum Sensing

To watch a nice interenergetic illustration comparing size of cells and microbes, check out the Cell Size and also Scale Resource at the University of Utah.

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Bacterial cell shape is established mainly by a protein dubbed MreB. MreB forms a spiral band – an easy cytoskeleton – approximately the inner of the cell simply under the cytoplasmic membrane. It is thneed to define shape by recruiting added proteins that then straight the specific pattern of bacterial cell growth. For example, bacillus-shaped bacteria that have actually an inset off MreB gene end up being coccoid shaped, and also coccus-shaped bacteria normally absence the MreB gene. Many bacteria come in one of three fundamental shapes: coccus, rod or bacillus, and also spiral.


The cocci are spherical or oval bacteria having one of numerous distinct arrangements (Figure (PageIndex2).1.1) based on their planes of division.


Figure (PageIndex2).1.1: Arrangement of cocci bacteria. photo provided via permission from Mariana Ruiz.

a. Division in one plane produces either a diplococcus or streptococcus plan.

diplococcus: cocci arranged in pairs (view Figure (PageIndex2))- scanning electron micrograph of a Streptococcus pneumoniae, a diplococcus; courtesy of CDC- scanning electron micrograph of a Neisseria, a diplococcus; courtesy of Dennis Kunkel"s Microscopy

streptococcus: cocci arranged in chains (watch Figure (PageIndex3))- scanning electron micrograph of a Streptococcus pyogenes, a streptococcus; courtesy of Dennis Kunkel"s Microscopy- transmission electron micrograph of Streptococcus from the Rockefeller University web web page.- scanning Electron Micrograph of Enterococcus

b. Division in 2 planes produces a tetrad plan.

tetrad: cocci arranged in squares of 4 (view Figure (PageIndex4))

- scanning electron micrograph of Micrococcus luteus reflecting several tetrads

c. Division in 3 planes produces a sarcina setup.

sarcina: cocci in arranged cubes of 8 (see Figure (PageIndex5))

d. Division in random planes produces a staphylococcus plan.

staphylococcus: cocci arranged in irconsistent, often grape-prefer clusters (check out Figure (PageIndex6))- negative picture of Staphylococcus aureus- scanning electron micrograph of Staphylococcus aureus, a staphylococcus; courtesy of Dennis Kunkel"s Microscopy- Scanning electron micrograph of methicillin-resistant Staphylococcus aureus (MRSA); courtesy of CDC

An average coccus is around 0.5-1.0 micrometer (µm) in diameter. (A micrometer equals 1/1,000,000 of a meter.)

The rod or bacillus

Bacilli are rod-shaped bacteria. Bacilli all divide in one plane developing a bacillus, streptobacillus, or coccobacillus setup (watch Figure (PageIndex7)).

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a. bacillus: single bacilli (check out Figure (PageIndex8))- scanning electron micrograph of a bacillus; courtesy of CDC- scanning electron micrograph of Escherichia coli O157H7, a bacillus; courtesy of CDC

b. streptobacillus: bacilli arranged in chains (see Figure (PageIndex9))

c. coccobacillus: oval and also similar to a coccus (check out Figure (PageIndex9)A and also Figure (PageIndex9)B)

An average bacillus is 0.5-1.0 µm wide by 1.0-4.0 µm lengthy.

The spiral

Spirals come in one of 3 forms, a vibrio, a spirillum, or a spirochete. (view Figure (PageIndex10))

a. vibrio: a curved or comma-shaped rod (view Figure (PageIndex11))- scanning electron micrograph of a Vibrio cholerae, a vibrio; courtesy of Dennis Kunkel"s Microscopy

b. spirillum: a thick, rigid spiral (view Figure (PageIndex12))

c. spirochete: a thin, flexible spiral (check out Figure (PageIndex13))- scanning electron micrograph of the spirochete Leptospira; courtesy of CDC- scanning electron micrograph of the spirochete Treponema pallidum; courtesy of CDC

Spirals range in size from 1 µm to over 100 µm in size.

Exceptions to the above shapes

There are exceptions to the 3 basic shapes of coccus, bacillus, and also spiral. They incorporate sheathed, stalked, filamentous, square, star-shaped, spindle-shaped, lobed, trichome-forming, and also pleomorphic bacteria.


Tbelow are three standard shapes of bacteria: coccus, bacillus, and spiral. Based on planes of department, the coccus shape can show up in a number of distinctive arrangements: diplococcus, streptococcus, tetrad, sarcina, and also staphylococcus. The bacillus shape have the right to appear as a single bacillus, a streptobacillus, or a coccobacillus. The spiral shape deserve to appear in a number of forms: vibrio, spirillum, and also spirochete. The metric unit micrometer (1/1,000,000 or 10-6 of a meter) is provided to measure bacterial dimension.