What is the Difference Between Bacteria and Mollicutes

The main difference between bacteria and mollicutes is that bacteria are single-celled organisms with a cell wall made up of peptidoglycans, whereas mollicutes are a type of bacteria with no cell wall.

Bacteria and mollicutes are two types of single-celled organisms and they are prokaryotes. Therefore, both organisms do not contain membrane-bound organelles.

Key Areas Covered

1. What are Bacteria
   • Definition, Characteristics, Importance
2. What are Mollicutes
   • Definition, Characteristics, Importance
3. Similarities Between Bacteria and Mollicutes
   • Outline of Common Features
4. Difference Between Bacteria and Mollicutes
   • Comparison of Key Differences

Key Terms

Bacteria, Mollicutes, Single-celled Organisms

What are Bacteria

Bacteria are unicellular prokaryotes that are freely-living biological cells of fewer micrometers long cells. Since bacteria are prokaryotes, they lack membrane-bound organelles such as nuclei, mitochondria, and chloroplasts. Generally, one of the main characteristic features of bacteria is the presence of a cell wall made up of peptidoglycans. Some bacteria contain an envelope surrounding the cell wall. Their genetic material occurs in the cytoplasm as a single circular DNA molecule. Another characteristic feature of bacteria is the presence of extrachromosomal DNA elements known as plasmids, which are important in recombinant DNA technology. Significantly, all of the biochemical reactions of the bacterial cell occur inside the cytosol.

Figure 1: Bacillus

Furthermore, the four major shapes in which bacteria can exist are bacillus (rod shape), coccus (spherical shape), spirilla (spiral shape), and Vibrio (curved shape). In addition, there are two types of bacteria based on the structure of the cell wall. They are Gram-positive and Gram-negative bacteria. Bacteria produce several types of responses to gaseous oxygen. Based on the response, bacteria can be classified as aerobic bacteria, which tend to live in the presence of oxygen, anaerobic bacteria, which tend to live without oxygen, and facultative anaerobes, which can live in both environments.

What are Mollicutes

Mollicutes are a class of bacteria that belong to the phylum Mycoplasmatota. The word “Mollicutes” is derived from the Latin meaning “soft skin”. Therefore, the main characteristic feature of mollicutes is that they lack a cell wall. Although mollicutes are a class of bacteria, they are very small in comparison to bacteria. Usually, the length of the mollicutes is 0.2–0.3 μm. The genome size of the mollicutes is smaller than the genome of bacteria.

Figure 2: Mycoplasma

Moreover, the cell membrane of mollicutes is somewhat rigid and it contains sterols. Therefore, mollicutes can move through gliding. However, the helical members of the mollicutes move through twisting; for example Spiroplasma. The most common type of mollicutes is Mycoplasma. In addition, the colonies of mollicutes have a fried egg appearance. Furthermore, mollicutes are parasites in animals and plants. Phytoplasma and Spiroplasma are plant pathogens associated with insect vectors. However, Mycoplasma is parasitic in humans and they attach to the cells in the respiratory or urogenital tracts.

Similarities Between Bacteria and Mollicutes

• Bacteria and mollicutes are prokaryotic organisms.
• They are single-celled organisms.
• Both can be Gram-positive.

Difference Between Bacteria and Mollicutes

Definition

Bacteria refer to a member of a large group of unicellular microorganisms which have cell walls but lack organelles and an organized nucleus, including some that can cause disease, while mollicutes refer to a class of bacteria distinguished by the absence of a cell wall.

Significance

Bacteria are prokaryotes while mollicutes are a class of bacteria.

Size and Cell Wall

Bacteria are unicellular organisms with a peptidoglycan cell wall while mollicutes are small organisms with no cell wall.

Gram Positive or Negative

Bacteria are either Gram-positive or negative while mollicutes are Gram-positive.

Genome Size

Bacteria have a large genome while mollicutes have a small genome.

Shape

The shape of bacteria can be either coccus, bacillus, vibrio, spirilla, and spirochaetes while the shape of mollicutes is either flask-shaped or coiled.

Habitat

Bacteria live in diverse habitats while mollicutes are parasitic.

Examples

E. coli, Clostridium difficile, and Streptococcus are examples of bacteria while mycoplasma and spiroplasma are examples of mollicutes.

Conclusion

In brief, bacteria and mollicutes are two types of single-celled prokaryotic organisms. Bacteria have large cells with peptidoglycan cell walls. But, mollicutes do not have a cell wall and they are small organisms. Therefore, the main difference between bacteria and mollicutes is their size and the presence of a cell wall. Moreover, bacteria can be either Gram-positive or Gram-negative while mollicutes are Gram-positive. In addition, bacteria live in a wide variety of habitats while mollicutes are parasites, living in other organisms. 

References:

1. Bacteria. Genome.gov. (n.d.). Retrieved September 26, 2022.
2. Mollicutes. An overview | ScienceDirect Topics. (n.d.). Retrieved September 26, 2022.

Image Courtesy:

1. “Bacillus subtilis 2” By Dr Graham Beards – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “b642-4 Mycoplasma pneumoniae. Photomicrograph, unstained. Note two isolated colonies adjacent to a single classical artifact, a ‘pseudocolony’ (750X) (Gabridge)” By Microbe World – Own Work (CC BY-NC-SA 2.0) via Commons Wikimedia