Bdellovibrio


Bdellovibrio

Taxobox
color = lightgrey
name = "Bdellovibrio"
regnum = Bacteria
phylum = Proteobacteria
classis = Delta Proteobacteria
ordo = Bdellovibrionales
familia = Bdellovibrionaceae
genus = "Bdellovibrio"
species = "B. bacteriovorus"
binomial = "Bdellovibrio bacteriovorus"
binomial_authority = Stolp & Starr 1963

"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, or over 100 times their length per second. It swims using a single sheathed polar flagellum with a characteristic dampened filament waveform. After a collision, the "Bdellovibrio" cell attaches to the prey cell outer membrane and peptidoglycan layer, after which it creates a small hole in the outer membrane. The "Bdellovibrio" cell then enters the host periplasmic space. It remains reversibly attached to it for a short "recognition" period. After the recognition period, it becomes irreversibly attached via the pole opposite the flagellum. Once inside the periplasm, the "Bdellovibrio" cell seals the membrane hole and converts the host cell to a spheroblast. A mixture of hydrolytic enzymes is applied in a locally targeted manner that prevents excessive damage to the prey and counters diffusion. 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".

References

http://www.ebi.ac.uk/2can/genomes/bacteria/Bdellovibrio_bacteriovorous.html

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