Types and Structure of Bacteria

Edited by Jen Moreau, TheGuyLoveNY, Sim



Bacteria (the singular is a bacterium) are single cell organisms that can live in different media. Some bacteria can survive in an acidic environment, such as the bacteria of the human gut and some others can survive in a saline medium such as the bacteria that live at the bottom of the ocean. Their sizes can vary; however, most bacteria are around 0.2μm in diameter and 2-8μm in length. Bacteria are classified under the prokaryotes because they lack membrane-bound organelles.

Was this helpful? Yes | No | I need help


Structure of bacteria

The structure of the bacterium is very simple as compared to the eukaryotic cells. A typical bacterium is shown and discussed below.

XX EX2 1.png

Cell wall

Bacteria are protected by rigid cell walls that form envelopes and surround the cells. The cell walls of bacteria are made of peptidoglycan, which is a polysaccharide chain. In gram-positive bacteria, the cell walls are thick, whereas, in gram-negative bacteria, they are thin. The cell wall of gram-negative bacteria is also surrounded by an extra thin layer membrane, composed of lipopolysaccharide and lipoproteins.

Was this helpful? Yes | No | I need help


Capsules are mainly present in pathogenic bacteria. The main function of a capsule is to protect the bacterium from the immune system of the host (the organism in which the bacteria can grow and live). Capsules are gel-like structures which may or may not have distinct boundaries.

Was this helpful? Yes | No | I need help


Flagella are responsible for the motility of the bacteria. They are thin structures of around 20μm, but long (3 to 12 μm), wavy filamentous appendages. A bacterium can have one flagellum or a cluster of flagella.

Was this helpful? Yes | No | I need help

Cytoplasmic Content

  1. 1
    These are folded invaginations that are present in the plasma membrane. These invaginations are important for the cellular respiration of the cell.
    Was this step helpful? Yes | No | I need help
  2. 2
    The ribosomes are small particles found in the cytoplasm. They are the sites where the translation of mRNA takes place, and also they are responsible for the synthesis of proteins.
    Was this step helpful? Yes | No | I need help
  3. 3
    Granular inclusions:
    These particles are not enclosed by a membrane and their main function is to act as storage units for the bacteria (Some are used to store glycogen for the bacteria that can be used later on to generate energy to the cell).
    Was this step helpful? Yes | No | I need help

Nuclear Body (Nucleoid)

bacterium 1.png

Apart from DNA and RNA, bacteria also contain plasmids. Plasmids are the circular DNA fragments present outside the nucleus. In the bacterial nucleus, densely aggregated DNA molecules are present, whereas in the cytoplasm RNA molecules are aggregated.

Was this helpful? Yes | No | I need help


Types of Bacteria

Bacteria can be classified based on different criteria.

1. Based on different survival conditions

  1. 1
    These bacteria thrive in normal conditions.
    Was this step helpful? Yes | No | I need help
  2. 2
    These bacteria thrive in extreme conditions such as very high or low temperature, high salt concentration or high pH
    Was this step helpful? Yes | No | I need help

2. Based on Gram Staining

  1. 1
    Gram-positive bacteria:
    These bacteria give a positive result to the gram staining test indicating the presence of a thick cell wall.
    Was this step helpful? Yes | No | I need help
  2. 2
    Gram- negative bacteria:
    These bacteria do not give a result for gram staining because of their thin peptidoglycan layer.
    Was this step helpful? Yes | No | I need help

3. Based on Structure

  1. 1
    These bacteria are spherical in shape. Example, Staphylococci
    Was this step helpful? Yes | No | I need help
  2. 2
    These bacteria have cylindrical or rod shaped structures.
    Was this step helpful? Yes | No | I need help
  3. 3
    These are spiral shaped bacteria
    Was this step helpful? Yes | No | I need help
  4. 4
    These bacteria have the shape of a comma.
    Was this step helpful? Yes | No | I need help
1109px-Bacterial morphology diagram.svg.png


Bacteria reproduce through a process called binary fission. In binary fission, a single cell is divided into two daughter cells. The cytoplasmic and nuclear contents of these cells are also divided, thus multiplying by 2n at each division.

Was this helpful? Yes | No | I need help

Three cell growth types.png

Referencing this Article

If you need to reference this article in your work, you can copy-paste the following depending on your required format:

APA (American Psychological Association)
Types and Structure of Bacteria. (2017). In ScienceAid. Retrieved Mar 25, 2017, from https://scienceaid.net/Bacteria

MLA (Modern Language Association) "Types and Structure of Bacteria." ScienceAid, scienceaid.net/Bacteria Accessed 25 Mar 2017.

Chicago / Turabian ScienceAid.net. "Types and Structure of Bacteria." Accessed Mar 25, 2017. https://scienceaid.net/Bacteria.

If you have problems with any of the steps in this article, please ask a question for more help, or post in the comments section below.


ScienceAid welcomes all comments. If you do not want to be anonymous, register or log in. It is free.

Ask the author

Featured Author
15 Articles Started
1,064 Article Edits
26,150 Points
JMoreau is a featured author with ScienceAid. JMoreau has achieved the level of "Lieutenant" with 26,150 points. JMoreau has started 15 articles (including this one) and has also made 1,064 article edits. 600 people have read JMoreau's article contributions.
JMoreau's Message Board
JMoreau: Hi, my name is JMoreau.
JMoreau: Can I help you with your problem about "Types and Structure of Bacteria"?

Article Info

Categories : Biochemistry

Recent edits by: TheGuyLoveNY, Jen Moreau

Share this Article:

Thanks to all authors for creating a page that has been read 56 times.

Do you have a question not answered in this article?
Click here to ask one of the writers of this article

Thank Our Volunteer Authors.

Would you like to give back to the community by fixing a spelling mistake? Yes | No