Multiple fission of multinucleoid filamentous cells:Bdellovibrio spp. - tiny predatory δ-proteobacteria that invade the periplasm of theprey bacterium and systematically consume itAttack phase Bdellovibrio cells - highly motile as they search for susceptible preyOnce host-contact is made, Bdellovibrio cells penetrate outer membrane of a preycell.Concealed within host, Bdellovibrio lyses the cell wall, which reduces prey to aspheroplast, and then Bdellovibrio assimilates organic compounds from the preycytoplasmBdellovibrio grows in prey periplasm, but this growth is not accompanied by celldivision — instead, cell elongates, forming a multinucleoid filamentous cell.Once the host cytoplasm is consumed, the Bdellovibrio reproduces: filamentundergoes multiple fission.The offspring produce flagella and emerge from the ‘spent’ host to search for otherprey - differentiate into motile attack-phase cells.Under these growth conditions, B. bacteriovorus has a filamentous growth phasethat is followed by a reproductive, multiple-fission phase.

Cells move rapidly in random directions untilencounter with prey.

Decreased velocity upon encounter of chemical trailof prey. (This is disputed). Trail consists of elevatedamino acid levels.

Attachment, and irreversible penetration occur.Penetration occurs by rapid rotations at speeds of upto 100rps & shedding of flagellum.

Now within the periplasm, the bacterium carriesout RNA, DNA, and protein synthesis.

Host cell envelope is converted into a bdelloplast- anenvelope with drastically altered morphology andcomposition.

Host is used only as a source of organic substrates.There is no reliance on host metabolism.

Growth cycle has unusually high efficiency.Bdellovibrio consumes up to 65% of host material.

Attachment of B. bacteriovorus

to Escherichia coli host

Despite the nutrient-rich environment of its hosts, Bdellovibrio maintains a

large 3.8Mb genome.

Two reasons for the large genome:

1. hydrolytic enzymes and sensor regulator systems required for entry and

digestion of prey are encoded for.

2. Life-style switching to host-independent (HI) form may contribute.

Host-dependent lifestyleIn this phase bacteria feed on conventional carbon sources.

Is rare & is thus thought to occur only by mutation (usually on gene

bd0108) events.

HI cells grow as long filaments. They septate into multiple progeny- some

are attack phase size and some are longer serpentine cells.

Bdellovibrio are considered as “versitalists” as they prey on diverse

bacteria and have potential to be prey-independent.

Exclusive use of inside of other Gram-negatives as food.

No competition.

Maximum niche exploitation- cellular contents don’t leak out of cell after invasion

as OM is resealed.

Protection by Bdelloplast while replicating.

Versitalist nature.

Horizontal Gene Transfer?Predatory life assures high degree of interaction with other bacteria- Potential for

HGT.

Degradation of host includes complex polymers though, including the genome.

There is reuse of host nucleic acids rather than lateral transfer.

Use of nucleases also acts against LGT.

Some evidence of HGT in the form of AT-rich genes thought to be laterally

transferred has been found.

BALOs- B. bdellovibrio-and-like-organisms- predate on other Gram-negative

organisms, including plant & human pathogens.

They can thus be used in the fight against increasingly antimicrobial resistant

infections, such as soft-tissue Acinetobacter baumannii infections, uropathogenic

E. coli infections, and nosocomial Pseudomonas infections.

Referred to as ‘living antibiotics’ in this context.

Are also effective in killing biofilm organisms and can be used against biofilm-

associated infections. They penetrate deeply inside prey biofilms and effectively

destroy them.

Can also be used in water purification

Possible disadvantages of these applications

Direct invasion of mammalian (or plant) cells.

Broad prey range could cause harmful imbalance of normal gut microbiota

(dysbiosis).

Possibility and extent still under investigation.