Bdellovibrio bacteriovorus: The bacteria that prey upon other bacteria

Many people have heard of bacteria that affect other living organisms (plants, animals, fungi, etc,) what is less known is that there are some bacteria that can attack other bacteria. The most notable predatory bacteria come from the genus Bdellovibrio, and one of the members of this genus is the Bdellovibrio bacteriovorus. This bacteria has raised a lot of suggestions in the field of therapy, some suggest the applicability as a weapon to combat gram-negative pathogenic bacteria just the way phages are used. Although the use of bacteria to treat bacterial infection has not created a lot of attention worldwide compared to phages, researchers predict that in case it is applicable it may bridge the remaining gaps (limitations) of phage therapy.
Bdellovibrio bacteriovorus Electron micrograph, 14,000 ×. Photo by Stolp and Starr (1963)

Bdellovibrio bacteriovorus

This bacterium is a Gram-negative obligate predatory bacterium that lives by attacking other Gram-negative bacteria. Bdellovibrio bacteriovorus was discovered in 1963 by Stolp and Starr. Like some of the famous discoveries, this bacteria was discovered unintentionally while attempting to isolate bacteriophages from a soil sample. The unusual lytic plaques observed made them suspect that they were dealing with something unique. Further investigations, uncovered that the growing plaques on the bacterial lawn were not caused by a bacteriophage but by a bacterium itself. The bacterium presented a phage-like life cycle (with some differences of cause), and its growth was contingent on the presence of prey.

Distribution

Bdellovibrio bacteriovorus can be found in the environment (water, soil, plants animals, and even in the human gut). Therefore, they can not be considered rare although their availability is affected by environmental factors (temperature, pressure, salinity e.t.c) and 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 and create a minute hole. The cell will enter through the hole to the host periplasmic space, during this time the bacteria remain reversibly attached. this event is termed as recognition period.
Later the bacteria will become irreversibly attached and enter the periplasm where it will seal the membrane hole. Due to enzyme L, D transpeptidases, the peptidoglycan layer of the host bacteria will be digested hence making the cell become amorphous. At this stage, the cell will appear spherical and this two-cell complex is termed as bdelloplast. The bdellovibrio will continue using host nutrients using hydrolytic enzymes to grow filamentously until when they are exhausted. After nutrient exhaustion the filament septates to form progeny Bdellovibrios. The progeny become motile before they lyse the host cell and are released into the environment.

2. Host independent

In this style, the bacteria will survive as normal bacteria do.

Can Bdellovibrio bacteriovorus be used for therapy?

Although not yet officially clinically tried by researchers, suggestions have been made based on laboratory experimentations. The bacteria is promising something that other methods like phage therapy are not able to offer. This can be used to overcome the limitations of phage therapy and in one way or another ensure the fight against AMR bugs is on our side. That is if it is practically possible on the field since this method of using bacteria to treat has a lot more other 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 completely the prey population
  • The inability to attenuate systemic blood infections
  • The skepticism associated with treating infections 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 wide 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 different 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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