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Vampirovibrio chlorellavorus
Vampirovibrio chlorellavorus is one of the few predatory bacteria. It was previously known as Bdellovibrio chlorellavorus. Unlike many bacteria, Vampirovibrio chlorellavorus is an obligate parasite, attaching to the cell wall of the phototrophic bacterium Chromatium and green algae of the genus Chlorella. V. chorellavorus is a 0.6µm pleomorphic cocci with a gram negative cell wall, found in freshwater. It can only divide when attached to its host, relying on host cellular contents for reproduction.

Etymology
Vampirovibrio originates from the Hungarian words vampir meaning vampire (due to the nature of sucking out cellular contents of its prey) and vibrio referring to the bacterial genus of curved rod bacterium. Chlorellavorus is named for the host of the bacterium (Chlorella) and the Latin voro meaning "to devour" (Chlorella-devouring).

Classification
The bacterium, first described by Gromov and Mamkayeva in 1972, was originally classified in the genus Bdellovibrio. It was then reclassified as its own genus Vampirovibrio in 1980 after being excluded from the genus Bdellovibrio for some essential discrepancies. Most significantly, Bdellovibrio is an extracellular parasite, both residing and dividing in the periplasmic space in its host. Vampirovibrio, however, is epibiotic, attaching to the cell wall of phototrophic bacterium. Furthermore, Vampirovibrio is non-motile, whereas Bdellovibrio is motile via a polar flagellum. Although upon initial discovery, Gromov concluded that Bdellovibrio chorellavorus utilized a thinner, uncovered flagellum differentiating the bacterium from Bdellovibrio bacteriovorus with a thick-sheathed flagellum.

Discovery and History
Gromov and Mamkaeva first isolated Bdellovibrio chlorellavorus in a lysis experiment with the algae Chlorella vulgaris from Ukranian reservoir waters from a mass culture of Chlorella Beijer in 1966. In a later experiment, the scientists were then able to cultivate B. chlorellavorus together with Chlorella vulgaris at 24 degrees Celsius and pH 6.8 in a liquid agar solution under fluorescent lighting (at an average of 2100 lux). In 1980, Gromov proposed a re-classification of Bdellovibrio chlorellavorus to Vampirovibrio chlorellavorus after finding that the organism exhibited certain characteristics that were not typical for organisms classified in the genus Bdellovibrio. These distinguishing characteristics include parasitizing the host cell without penetration and the presence of a flagellum that was not as thick or sheathed like other Bdellovibrio organisms.

Preliminary Characterization
Vampirovibrio chlorellavorus is a gram-negative obligate aerobic bacteria with a curved comma shape .The bacterium attaches to the surface of purple sulfur bacterium in the genus Chromatium and green algae of the genus Chlorella. V. chlorellavorus is an extracellular parasite and remains attached to the cell wall. Once attached to its host, V. chlorellavorus divides by binary fission, destroying its host in the process by “sucking out” all of the cellular contents via peripheral vacuoles much like a vampire (hence the name Vampirovibrio). V. chlorellavorus leaves behind only the cell wall and cytoplasmic membrane of Chromatium along with a few intracytoplasmic inclusions. V. chlorellavorus is a non-motile anaerobe and will not grow in axenic cultures, depending on access to living cells of its preferred algae host, "Chlorella vulgaris" for reproduction. The genome has been partially sequenced and is listed under strain ATCC 29753. With a GC content of approximately 50 percent, the genome is relatively stable.

Genomics
Dr. Hugenholtz and team, of the University of Queensland in Australia, have completed shotgun sequencing of lyophilized cells of V. chlorellavourus in joint culture with Chlorella vulgar. They found that V. chlorellavorus uses a type IV secretion system (T4SS), similar to to that of Agrobacter tumefaciens for host invasion, which is conserved in all three copies of the V. chlorellavorus genome. They also determined V. chlorellavorus to be a non-photosynthetic Cyanobacterium. As a result of these findings, Dr. Hugenholtz and his team proposed an alternate classification of V. chlorellavorus in phylum Cyanobacteria, proposed class Melainabacteria, order Vampirovibrionales, and family Vampirovibrionaceae. Compared to members of the genus Bdellovibrio, Vampirovibrio is epibiotic, parasitizing its host from the outside. The Vampirovibrio life cycle consists of: prey location, attachment, ingestion, binary division, and release. After Soo and Hugenholtz' team performed a genomic reconstruction in 2010 from a culture deposited into the NCIB collection in 1978, they were able to make a general metabolic reconstruction of the genome as well. To locate its prey, V. chlorellavorus seems to be equipped with possible genes for aerotaxis and light activated kinase (moving towards light). To digest its algal prey, V. chlorellavorus has over 100 hydrolytic enzymes including proteases and peptidases. From the results of Soo and her team's genomic analysis, V. chlorellavorus has approximately 26 contigs, 2.91 Mbp, an average GC content of 51.4%, and 2 circular plasmids. In keeping with its description as non-photosynthetic and parasitic microorganism, V. chlorellavorus does not have its own genes for photosynthesis or carbon fixation. V. chlorellavorus is however capable of synthesizing its own nucleotides, certain cofactors and vitamins, and 15 different amino acids. Its bacterial genome also includes coding for a complete glycolysis pathway as well as an electron transport chain.

Current Research and Implications
Using 16S rRNA analysis, scientists have estimated that this bacterium most closely belongs to the SM1D11 lineage of bacteria. In addition, when compared to other Cyanobacteria, Vampirovibrio is non-photosynthetic and could possibly belong to a new proposed classification called Melainobacteria, from Greek root words meaning “nymph of dark waters.” Vampirovibrio or Bdellovibrio could be used to help control harmful populations of bacteria due to its predatory nature. In an experiment where Bdellovibrio were added to a shrimp tank to consume populations of bacteria, the target bacterial populations declined by up to 44%. Also, the Bdellovibrio population declined after consuming most of the available bacteria. Therefore, use of Bdellovibrio as an inhibitor of other bacteria shows potential, but may be limited to certain cases as Bdellovibrio prefers certain strains, such as gram-negative bacteria. However the results of a subsequent experiment show more potential. Chickens, highly susceptible to cecal or gut infections, were used in an experiment in which scientists purposely infected chickens with a pathogenic form of Salmonella enterica. The chicken were then exposed to Bdellovibrio bacteriovorus, after which a reduction in inflammation and other harmful changes in the chickens’ ceca were observed as a result of decreased Salmonella populations. The success of this experiment suggest there is significant potential for Bdellovibrio in bioremediation. Since Vampirovibrio chlorellavorus has not been cultured in recent years, it is possible to learn about its future research applications by learning about the methods in which Bdellovibrio and like organisms or BALOs are used to control pathogenic bacteria.