Bdellovibrio
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''Bdellovibrio'' is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...
,
obligate aerobic {{wiktionary, obligate As an adjective, obligate means "by necessity" (antonym ''facultative'') and is used mainly in biology in phrases such as: * Obligate aerobe, an organism that cannot survive without oxygen * Obligate anaerobe, an organism that ...
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
. One of the more notable characteristics of this genus is that members can
prey Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
upon other Gram-negative bacteria and feed on the
biopolymer Biopolymers are natural polymers produced by the cells of living organisms. Like other polymers, biopolymers consist of monomeric units that are covalently bonded in chains to form larger molecules. There are three main classes of biopolymers, cl ...
s, 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 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 periplasm is a concentrated gel-like matrix in the space between the inner cytoplasmic membrane and the bacterial outer membrane called the ''periplasmic space'' in gram-negative bacteria. Using cryo-electron microscopy it has been found that ...
. 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. Using some of these molecules the ''Bdellovibrio'' creates a protective environment by reinforcing the
peptidoglycan Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like peptidoglycan layer outside the plasma membrane, the rigid cell wall (murein sacculus) characteristic of most ...
cell wall of the host in which it now dwells using
amidase In enzymology, an amidase (, ''acylamidase'', ''acylase (misleading)'', ''amidohydrolase (ambiguous)'', ''deaminase (ambiguous)'', ''fatty acylamidase'', ''N-acetylaminohydrolase (ambiguous)'') is an enzyme that catalyzes the hydrolysis of an ami ...
s 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 flagella 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. This species is more capable of host-independent growth. Little is known of ''Bdellovibrio exovorus'', 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 The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...
in size with a barely discernible
flagellum A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...
. ''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. ''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 ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...
'' S-17 at 29°C for 16 hrs. They may also be cultured using YPSC (yeast extract, peptone, sodium acetate, calcium chloride) overlays or
prey lysates Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
.


Life cycle and parasitism

''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 A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...
with a characteristic dampened filament waveform. ''Bdellovibrio'' attacks other Gram-negative bacteria by attaching itself to the prey cell's outer membrane and
peptidoglycan Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like peptidoglycan layer outside the plasma membrane, the rigid cell wall (murein sacculus) characteristic of most ...
layer, after which it creates a small hole in the outer membrane. The ''Bdellovibrio'' cell then enters the host
periplasmic space The periplasm is a concentrated gel-like matrix in the space between the inner cytoplasmic membrane and the bacterial outer membrane called the ''periplasmic space'' in gram-negative bacteria. Using cryo-electron microscopy it has been found that ...
. 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 Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis ...
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
s 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''. Targets of ''Bdellovibrio'' species, including ''
Vibrio vulnificus ''Vibrio vulnificus'' is a species of Gram-negative, motile, curved rod-shaped (bacillus), pathogenic bacteria of the genus ''Vibrio''. Present in marine environments such as estuaries, brackish ponds, or coastal areas, ''V. vulnificus'' is relat ...
'', may undergo co-infection by ''Bdellovibrio'' and
bacteriophage A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν ('), meaning "to devour". Bacteri ...
. 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. The HD100 genome is
nucleotide Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules wi ...
s long, larger than expected given its small size.


References


External links

* * {{Taxonbar, from=Q136602 Oligoflexia Gram-negative bacteria Bacteria genera