Difference Between Spirilla and Spirochetes

Key Difference – Spirilla vs Spirochetes
 

Microorganisms are mainly classified as Bacteria, Cyanobacteria, Fungi, and Protists. Bacteria are further classified on the basis of their shape, nutritional patterns, and metabolic characteristics. Based on the shape, there are two main genera that belong to the spiral-shaped bacteria namely Spirilla and Spirochetes. Spirilla are spiral-shaped bacteria that have a rigid cell wall and utilize polar flagella for its locomotion. Spirochetes are spiral-shaped bacteria that have a flexible cell wall and possess axial filaments for its motility. The key difference between the Spirilla and Spirochetes are based on their different structures utilized for motility. Spirilla possess polar flagella, whereas Spirochetes possess axial filaments for their need of locomotion.

CONTENTS

1. Overview and Key Difference
2. What are Spirilla
3. What are Spirochetes
4. Similarities Between Spirilla and Spirochetes
5. Side by Side Comparison – Spirilla vs Spirochetes in Tabular Form
6. Summary

What are Spirilla?

Spirilla (singular – Spirillum) are spiral-shaped bacteria of 1.4 – 1.7 micrometers in diameter and 60 micrometers in length. Spirilla are gram-negative, chemoorganotrophic bacteria. Spirilla can be found in freshwater and they can also act as biological indicators of water pollution. These spiral shapes bacteria have a rigid cell wall structures. The storage granules are composed of volutin, which are intracytoplasmic organic granules complexed with inorganic phosphates. Volutins substitute the poly beta-hydroxybutyrate granules found commonly in bacteria.

The locomotion of the spirilla species is a distinguishing factor from other spiral-shaped bacteria such as Spirochetes. They possess polar flagella for locomotion. Initially, it was thought that spirilla are composed of one polar flagella fascicle. At present some species are thought to have multiple flagella fascicles. These multiple flagella fascicles aggregate to form one flagellum. During the staining process, usually, only one flagellum is observed in Spirilla. The flagella of Spirillum spans for a length of about 3 micrometers and is nearly one wave in length. The mechanism of the bipolar flagella movement is described by many scientists. In a broader context, it is said to rotate the cell body in the opposite direction of the flagellar rotation. Therefore, it is said to depict a corkscrew type movement.

Spirilla are characterized as microaerophilic organisms, where they require 1% – 9% of oxygen for their survival. The other biochemical features of spirilla are listed below.

• Weak catalase activity.
• Strong oxidase and phosphatase activity.
• Inability to reduce nitrate. Therefore, cannot utilize nitrates.
• Do not oxidize or ferment carbohydrates.

Some spirilla organisms can be categorized as disease-causing bacteria, where the species S. minor is a cause of rat bite fever in humans.

What are Spirochetes?

Spirochetes are spiral-shaped gram-negative, chemoheterotrophic bacteria, about 3 – 500 micrometers in length. They are commonly found in freshwater environments. They are motile bacteria, and they have specialized structures known as axial filaments for locomotion. Each spirochete may contain up to 100 axial filaments where the lowest would be two axial filaments per organism. The significance of the axial filaments is its position. The axial filaments, unlike flagella, run between the inner and the outer membrane of the spirochete. Therefore, the axial filaments arise from the periplasmic surface. Some species of spirochetes contain bundles of fibrils in the cytoplasm, these cytoplasmic fibrils are observed in response to different stress conditions in spirochetes. Most Spirochetes are anaerobic and they reproduce by binary fission, which is an asexual mode of reproduction commonly observed in Bacteria.

Spirochetes are important bacteria when it comes to its involvement in pathogenesis. The host – spirochete relationship has been shown to be harmful as most species are disease-causing. The genera of spirochetes including Spirochaeta, Treponema, Borrelia, and Leptospira are involved in causing deadly diseases.

• Treponema ssp
  • Treponema pallidum pallidum – Syphilis
  • Treponema pallidum pertenue – Yaws
• Borrelia ssp
  • Borrelia recurrentis – Relapsing fever (transmitted by lice and ticks)
  • Borellia burgdorferi – Lyme disease
• Leptospira ssp – Leptospira

What are the Similarities Between Spirilla and Spirochetes?

• Both Spirilla and Spirochetes groups are Gram-negative bacteria.
• Both Spirilla and Spirochetes organisms can be found in the freshwater environments.
• Both Spirilla and Spirochetes are spiral-shaped bacteria.
• Both Spirilla and Spirochetes are motile organisms.
• Both Spirilla and Spirochetes can cause diseases.

What is the Difference Between Spirilla and Spirochetes?

Summary – Spirilla vs Spirochetes 

Spirilla and Spirochetes are spiral-shaped bacteria that show contrasting features in their motility patterns. Spirilla use bipolar flagella to support their locomotion, whereas Spirochetes use many axial filaments arising from the periplasmic space to support their locomotion. Both are Gram-negative bacteria and they are involved in manifesting diseases. Spirochetes result in more deadly diseases when compared to the species of Spirilla. This is the difference between spirilla and spirochetes.

Reference:

1.Holt, S C. “Anatomy and chemistry of spirochetes.” Microbiological Reviews, U.S. National Library of Medicine, Mar. 1978. Available here  
2.Krieg, N R. “Biology of the chemoheterotrophic spirilla.” Bacteriological Reviews, U.S. National Library of Medicine, Mar. 1976. Available here

Image Courtesy:

1.’Spirillen’By Wolframm Adlassnig – Own work, (Public Domain) via Commons Wikimedia
2.’Leptospira interrogans strain RGA 01’By Obtained from the CDC Public Health Image Library. (Public Domain) via Commons Wikimedia