Bdellovibrio

Bdellovibrio is a genus of Gram-negative, obligate aerobic bacteria. One of the more notable characteristics of this genus is that members can prey upon other Gram-negative bacteria and feed on the biopolymers, e.g. proteins and nucleic acids, of their hosts. They have two lifestyles: a host-dependent, highly mobile phase, the "attack phase", in which they form "bdelloplasts" in their host bacteria; and a slow-growing, irregularly shaped, host-independent form.

Bdellovibrio
Central slice through a cryotomogram of an intact Bdellovibrio bacteriovorus cell. Scale bar 200 nm
Scientific classification
Kingdom:	Bacteria
Phylum:	Proteobacteria
Class:	Oligoflexia
Order:	Bdellovibrionales
Family:	Bdellovibrionaceae
Genus:	Bdellovibrio
Species:	B. bacteriovorus
Binomial name
Bdellovibrio bacteriovorus Stolp & Starr 1963

Bdellovibrio bacteriovorus

The most well studied of these is Bdellovibrio bacteriovorus, which is found almost exclusively in host dependent growth in nature. In this free swimming attack form after searching for prey using its pili, it burrows through the host outer membrane/ peptidoglycan cell wall and enters the periplasmic space. The Bdellovibrio bacterium then forms a structure called a bdelloplast. This bdelloplast is created as the host cell is modified to become spherical in shape. Inside the bdelloplast, the singular large flagellum of the predatory Bdellovibrio is lost. The host cell is then rapidly killed allowing the passage of molecules from the interior of the host cytoplasm through to the periplasm freely, and the periplasm dwelling Bdellovibrio to feed.[1] Using some of these molecules the Bdellovibrio creates a protective environment by reinforcing the peptidoglycan cell wall of the host in which it now dwells using amidases and transpeptidases. After around 4hrs, depending on ambient temperature, the Bdellovibrio has increased in size dramatically through this nourishment. It divides to replicate and then leaves via a final lysis of the host's cell wall and membranes. The newly emerging Bdellovibrio use their newly grown powerful flagellar to swim away and find the next suitable host. Because of this intermittent bdelloplast stage, and momentary parasitic phase (15-20 mins), Bdellovibrio could be considered bacterial predators or parasites.

Bdellovibrio bacteriovorus was first described by Stolp and Petzold in 1962. In 2012 another member of the Bdellovibrio species was identified "Bdellovibrio tiberius" of the River tiber.[2] This species is more capable of host-independent growth.

Little is known of Bdellovibrio exovorus,[3] an extra-parasitic bdellovibrio, which cannot enter its prey, and does not form Bdelloplasts.

Appearance

Under a light microscope, host-dependent Bdellovibrio appears to be 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. Bdellovibrio show up as a growing clear plaque in an E. coli “lawn”. Notably, Bdellovibrio has a sheath that covers its flagellum – a rare feature for bacteria. Flagellar motion stops once Bdellovibrio has penetrated its prey, and the flagella is then shed.

Host-independent Bdellovibrio appear amorphous, and larger than the predatory phase.

Culture conditions

B. bacteriovorus appears to be ubiquitous in nature and manmade habitats. They have been found in soil samples, rhizosphere of plant roots, rivers, oceans, sewage, intestines and feces of birds and mammals, and even in oyster shells and the gills of crabs.[4] B. bacteriovorus are able to thrive in almost any habitat, the general requirements are that there needs to be oxygen and some other Gram-negative bacteria present in its environment. Its optimal temperature is between 28-30°C, making B. bacteriovorus a mesophile. Bdellovibrio is grown in the laboratory in its stationary HI (host-independent) phase at 29°C on yeast peptone broth agar. Host-dependent (predatory) cultures are grown with a population of E. coli S-17 at 29°C for 16 hrs.[2] They may also be cultured using YPSC (yeast extract, peptone, sodium acetate, calcium chloride) overlays or prey lysates.

Life cycle and parasitism

Bdellovibrio Life Cycle. The Bdellovibrio attaches to a Gram-negative bacterium after contact, and penetrates into the prey's periplasmic space. Once inside, elongation occurs and progeny cells are released within 4 hours.[5]

Bdellovibrio cells can swim as fast as 160 µm/s, or over 100 times their body-length per second. It swims using a single sheathed polar flagellum with a characteristic dampened filament waveform. Bdellovibrio attacks other Gram-negative bacteria by attaching itself to the prey cell's 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 spherical morphology, this is due to secretion of L,D transpeptidases which breaks the peptidoglycan apart, and therefore causes the cell to become amorphous. The two-cell complex formed is called a bdelloplast. The Bdellovibrio cell uses hydrolytic enzymes to break down the host cell molecules, which it uses to grow filamentously. 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 three to four hours, and produces an average of 3–6 progeny cells from a single E. coli, or up to 90 from larger prey such as filamentous E. coli.[6]

Targets of Bdellovibrio species, including Vibrio vulnificus, may undergo co-infection by Bdellovibrio and bacteriophage.[7] Although the Bdellovibrio rounding of prey is thought to be evolved to reduce co-infection of multiple Bdellovibrio, larger prey that do not round may be infected by multiple Bdello's.

Genomics

The genome of Bdellovibrio bacteriovorus HD100 was sequenced in 2004.[8] The HD100 genome is 3782950 nucleotides long, larger than expected given its small size.[9]

References

1. Rittenberg SC, Shilo M (April 1970). "Early host damage in the infection cycle of Bdellovibrio bacteriovorus". Journal of Bacteriology. 102 (1): 149–60. PMC 284981. PMID 4908670.
2. Hobley L, Lerner TR, Williams LE, Lambert C, Till R, Milner DS, et al. (November 2012). "Genome analysis of a simultaneously predatory and prey-independent, novel Bdellovibrio bacteriovorus from the River Tiber, supports in silico predictions of both ancient and recent lateral gene transfer from diverse bacteria". BMC Genomics. 13: 670. doi:10.1186/1471-2164-13-670. PMC 3539863. PMID 23181807.
3. Koval SF, Hynes SH, Flannagan RS, Pasternak Z, Davidov Y, Jurkevitch E (January 2013). "Bdellovibrio exovorus sp. nov., a novel predator of Caulobacter crescentus". International Journal of Systematic and Evolutionary Microbiology. 63 (1): 146–151. doi:10.1099/ijs.0.039701-0. PMID 22368169.
4. Shemesh, Y. (2003). "Small eats big: Ecology and diversity of Bdellovibrio and like organisms, and their dynamics in predator-prey interactions". Agronomie. 23: 433–439.
5. Madigan, Michael T. (7 January 2011). Brock Biology of Microorganisms (Global ed.). Pearson Education. ISBN 978-0-321-73551-5.
6. Strauch, E.; Beck, S.; Appel, B. (2007). "Bdellovibrio and like organisms: Potential sources for new biochemicals and therapeutic agents?". Predatory Prokaryotes. Microbiology Monographs. 4. p. 131. doi:10.1007/7171_2006_055. ISBN 978-3-540-38577-6.
7. Chen, H.; Williams, H.N. (2012). "Sharing of prey: Co-infection of a bacterium by a virus and a prokaryotic predator". mBio. 3 (2): e00051-12. doi:10.1128/mBio.00051-12. PMC 3345577. PMID 22511350.
8. Rendulic S, Jagtap P, Rosinus A, Eppinger M, Baar C, Lanz C, Keller H, Lambert C, Evans KJ, Goesmann A, Meyer F, Sockett RE, Schuster SC (January 2004). "A predator unmasked: Life cycle of Bdellovibrio bacteriovorus from a genomic perspective". Science. 303 (5658): 689–692. doi:10.1126/science.1093027. PMID 14752164.
9. Tudor, J. J.; McCann, M. P. (2007). "Genomic analysis and molecular biology of predatory prokaryotes". Predatory Prokaryotes. Microbiology Monographs. 4. p. 153. doi:10.1007/7171_056. ISBN 978-3-540-38577-6.

External links

• "Bdellovibrio genome".
• "Type-strain of Bdellovibrio bacteriovorus at Bac Dive". The Bacterial Diversity Metadatabase.