Bdellovibrio bacteriovorus: The bacteria that prey upon other bacteria

Many people are aware that bacteria can harm other living organisms (plants, animals, fungi, and so on); however, it is less well known that some bacteria can attack other bacteria. The genus Bdellovibrio contains the most well-known predatory bacteria, such as Bdellovibrio bacteriovorus. This bacteria has sparked a lot of interest in the field of therapy; some believe it could be used as a weapon against gram-negative pathogenic bacteria in the same way that phages are. Although the use of bacteria to treat bacterial infections has received less attention than phage therapy, researchers believe that if it is effective, it may bridge the remaining gaps (limitations) of phage therapy.

Electron micrography of bdellovibrio bacteriovorus
Bdellovibrio bacteriovorus Electron micrograph, 14,000 ×. Photo by Stolp and Starr (1963)

Bdellovibrio bacteriovorus

This bacterium is an obligate predatory Gram-negative bacterium that survives by attacking other Gram-negative bacteria. Stolp and Starr discovered Bdellovibrio bacteriovorus in 1963. This bacteria, like some other famous discoveries, was discovered unintentionally while attempting to isolate bacteriophages from a soil sample. The unusual lytic plaques observed led them to believe they were dealing with something special. Further research revealed that the growing plaques on the bacterial lawn were caused by a bacterium rather than a bacteriophage. The bacterium had a phage-like life cycle (with some differences in the cause), and its growth was dependent on the presence of prey.

Distribution

Bdellovibrio bacteriovorus can be found in nature (water, soil, plants, animals, and even in the human gut). As a result, they are not considered rare, even though their availability is influenced by environmental factors (temperature, pressure, salinity, and so on) as well as the availability of prey.

Life cycle

Bdellovibrio bacteriovorus cycle has got two lifestyles, host-dependent, and host-independent.
Life cycle of Bdellovibrio bacteriovorus. Photo by Cavallo et al, 2020


1. Host dependent

In this lifestyle, the bacteria attach to the outer membrane and peptidoglycan layer of gram-negative bacteria, creating a minute hole. The cell will enter the host periplasmic space through the hole, and the bacteria will remain reversibly attached during this time. This is known as the recognition period.
The bacteria will eventually become irreversibly attached and enter the periplasm, sealing the membrane hole. The peptidoglycan layer of the host bacteria is digested by the enzyme L, D transpeptidases, causing the cell to become amorphous. At this stage, the cell will appear spherical, and the two-cell complex is known as bdelloplast. The bdellovibrio will continue to grow filamentous by using host nutrients and hydrolytic enzymes until they are depleted. After nutrient exhaustion, the filament septated to form progeny Bdellovibrios. The progeny become motile before they lyse the host cell and are released into the environment.

2. Host independent

The bacteria will survive in the same way that normal bacteria do by binary fusion as a mode of reproduction.

Can Bdellovibrio bacteriovorus be used for therapy?

Although researchers have not yet officially tried, suggestions based on laboratory experiments have been made. The bacteria offers something that other methods, such as phage therapy, cannot. This can be used to overcome the limitations of phage therapy and, in some way, ensure that we have a fighting chance against AMR bugs. That is if it is practically possible on the field because this method of treating bacteria has far more limitations than other therapies covered.

Advantages of using Bdellovibrio bacteriovorus for therapy

  • They have a broad range of activity 
  • Transfer of AMR genes that confer resistance to predation hasn't been reported. (Read on how bacteriophages transfer these AMR genes)
  • High efficiency in tackling biofilm 
  • Absence of specific resistance towards them

Disadvantages of using Bdellovibrio bacteriovorus for therapy

  • Less specificity may affect the normal flora
  • Inability to eradicate the prey population completely
  • The failure to attenuate systemic blood infections
  • The skepticism associated with treating conditions with live bacteria 
  • Potential transmission of AMR genes (although not yet reported)

Differences between Bacteriophages and Bdellovibrio bacteriovorus

Bacteriophages

Bdellovibrio bacteriovorus

They are viruses They are bacteria
They have a narrow host range They have a broad host range
Their life cycle depends on the host only (they can not exhibit living character on their own) They can survive and exhibit living characters with or without the host
Different phages prey on other bacteria (gram-positive and gram-negative) Prey on gram-negative bacteria only

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REFERENCE ARTICLES

  1. Francis M. Cavallo, Lorea Jordana, Alexander W. Friedrich, Corinna Glasner & Jan Maarten van Dijl (2021) Bdellovibrio bacteriovorus: a potential 'living antibiotic' to control bacterial pathogens, Critical Reviews in Microbiology, 47:5, 630-646, DOI: 10.1080/1040841X.2021.1908956.
  2. Stolp, H., Starr, M.P. Bdellovibrio bacteriovorus gen. et sp. n., a predatory, ectoparasitic, and bacteriolytic microorganism. Antonie van Leeuwenhoek 29, 217–248 (1963). https://doi.org/10.1007/BF02046064.

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