Bdellovibrio

Bdellovibrio is a genus of Gram-negative, obligate aerobic bacteria.

One of the more notable characteristics of this genus is that members parasitize other Gram-negative bacteria by entering into their periplasmic space and feeding on the biopolymers, e.g. proteins and nucleic acids, of their hosts. After entering the periplasmic space of its host the Bdellovibrio bacterium forms a structure called a bdelloplast, which consists of both predator and prey. The predator cell can remain dormant at this stage, without affecting the viability of the host. In most cases, though, Bdellovibrio devours its prey and moves on.

Bdellovibrio species are found in river water or soil and live an intraperiplasmic existence. To enrich for Bdellovibrio use NB/500 (nutrient broth at 1:500 dilution) and mix with hot soft agar with E. coli at 30 °C for one week.

Under the microscope, a Bdellovibrio appears as a comma-shaped motile rod that is about 0.3-0.5 by 0.5-1.4 µm in size with a barely discernible flagellum. Colonies of Bdellovibrio show up as a growing clear plaque in an E. coli lawn.

Another notable feature of Bdellovibrio is the sheath that covers its flagellum. This is a rare characteristic among bacteria. Flagellar motility stops after Bdellovibrio penetrates its prey. In some cases the flagella is shed; in others it protrudes from the outer membrane of the prey cell.

Bdellovibrio attacks other gram-negative bacteria by colliding with them at speeds recorded up to 160 µm/s: over 100 times their length per second! After a collision, the Bdellovibrio cell attaches to the prey cell outer membrane and creates a small hole in the outer membrane. The Bdellovibrio cell then enters the host periplasmic space. Once inside the periplasm, the Bdellovibrio cell seals the membrane hole and converts the host cell to a spheroblast. This two-cell complex is now called a bdelloplast. The Bdellovibrio cell uses hydrolytic enzymes to break down the host cell molecules, which it uses to elongate and form a filament. When the host cell nutrients are exhausted, the filament septates to form progeny Bdellovibrios. The progeny become motile before they lyse the host cell and are released into the environment. The entire life cycle takes from one to three hours, and produces an average of 3-6 progeny cells are from a single E. coli, or up to 80 from larger prey, such as filamentous E. coli.

Bdellovibrio bacteriovorus was first described by Stolp and Starr in 1963. Two other species, Bdellovibrio starrii and Bdellovibrio stolpii, have been moved to a separate genus Bacteriovorax.