Chromobacterium violaceum

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A Microbial Biorealm page on the genus Chromobacterium violaceum

Classification

Higher Order Taxa

Bacteria; Proteobacteria; Betaproteobacteria; Neisseriales; Neisseriaceae [Others may be used. Use NCBI link to find]

Species

NCBI: Taxonomy

Chromobacterium; Chromobacterium violaceum

Description and Significance

Chromobacterium violaceum is a facultative anaerobic, oxidase-positive, glucose-fermenting, non-lactose-fermenting, Gram-negative bacillus. It produces a possible antioxidant called violacein, a purple pigment that gives Chromobacterium violaceum its color. (7) Violacein has been studied and proven to defend microorganism membranes from oxidation or peroxidation. (8) This bacterium can also produce acid (ferment) from glucose, trehalose, N-acetylglucosamine and gluconate, but not L-arabinose, D-galactose or D-maltose. In addition, it can produce cyanide in the form of ammonium cyanide. Lastly, casein is hydrolyzed and arginine decarboxylated in the presence of this bacterium. (3) C. violaceum is also known for being a reporter strain in quorum sensing. (4) Quorum sensing is a phenomenon in which cells perform certain kinds of actions only in specific populations. It is a type of communication used by cells that allows cells to take specific actions when the population grows beyond a certain limit. (11)

Genome Structure

Its complete genome sequence consists of 64% GC content and therefore, 36% AT content. With 4,751,080 base pairs, C. violaceum has a circular genome with double-stranded DNA. (1) Besides the specifics, the genome shows extensive energy generating pathways, about 500 open reading frames devoted to proteins for transport, complex systems for adapting to stress, oxidation, and motility. Pretty much the genome contains all the aspects of having the multifaceted and the flexibility for this bacterium. On the other hand, the genome also consists of incomplete arrays of open reading frame coding for proteins that maybe linked to the severe symptoms of human C. violaceum infection. In other words, virulence genes have been found during genome sequencing (2), and the search of components of the main DNA repair pathways in this bacterium, revealed a great versatility as all the pathways were found present. (12)

Cell Structure and Metabolism

C. violaceum is abundantly present in soil and water in the tropical and subtropical regions. They usually reside in fresh bodies of water, but not in the normal human flora. Slightly curved rods, C. violaceum can range from medium to long lengths, and have rounded ends. Colonies are optimally produced during incubation at 22°C while cultured in 5% sheep blood agar under anaerobic conditions. Other agars such as MacConkey agar, and chocolate agar can also be used to cultivate this organism. Colonies appear black or very dark purple and give a smell of ammonium cyanide. (7)

C. violaceum is known for its adaptability to metabolize in aerobic and anaerobic conditions. The main factor that plays in this part is a flexible and efficient energy-generating metabolism. In aerobic conditions, the organism cannot synthesize glucose to produce energy and thus, resort to process such as Embden-Meyerhoff pathway, tricarboxylic acid, and other respiratory chains to produce cellular energy. ATP is produced under aerobic conditions. As for anaerobic conditions, the bacterium metabolizes glucose to produce organic acids such as acetic acid and formic acid. In other words, fermenting takes place due to low levels of oxygen. Also, soluble fats and peptides are metabolized for producing energy and by-products such as violacein. (5)

Ecology

C. violaceum is known to exist in both soil and water. (3) There has been a recording of possible C. violaceum in humic lake. Humic lake is a body of water rich with organic matter decomposed of plant and animal matter. The bacterium found did utilize glucose and other organic acids, possibly for energy, from the humus. (9)

Pathology

C. violaceum can only affect humans through intake of contaminated water or seafood or through exposure of open skin to contaminated soil or water. Although incidents of infections have been very rare, once infected, the symptoms are severe. The initial symptoms are inflammation of the tissue or glands such as cellulitis or lymphadenitis. Later, infections involving pus, also known as abscess, to the organs along with septic shock can occur. These infections can occur suddenly and severely possibly leading to a life-threatening situation. There are currently no vaccines for this infection, but antibiotics that contain active agents such as cefotaxime, cefrazidime, imipenem, and aminoglycosides are therapeutic. (7) An example that shows the degree of infection is when an adult Chinese red panda died in a week after being transported to a zoo in North Dakota. The reason, in simple terms, was that there were inflammations in the liver, lung, lymph node, and spleen. C. violaceum was detected, isolated, cultured, and was injected into mice. The mice died 18 hours later. The virulence of this bacterium is known to be irregular as both humans and animals can unexpectedly be infected severely. (6) Another example is that C. violaceum has been known to be toxic to insects and pests such as the Colorado potato beetle larvae. Living in soil, the bacterium poisons the insects after the insects consume plants and soil together. Because of this, it is known this bacterium does have negative affects on humans and insects. (10)

Current Research / Application to Biotechnology

C. violaceum produces a number of interesting proteins. They include paraquat-inducible proteins, drug and heavy-metal-resistance proteins, multiple chitinases, and proteins for the detoxification of xenobiotics. All of these proteins and metabolites may have biotechnological applications. Research is currently being performed to acknowledge these assumptions. (2) As for the known substances, in addition to violacein, other antibiotics produced from C. violaceum are aerocyanidine, aerocavin, 3,6-dihydroxyindoxazene, and Factor Y-T0678H. Out of the four antibiotics, aerocyanidine specifically works against Gram-positive organisms whereas 3,6-dihydroxyindoxazene and factor Y-T0678H are substances that only work against Gram-negative organisms. As for aerocavin, both Gram-positive and negative don’t survive well in its presence. Simply, C. violaceum is well-known for the antibiotics it produces, and those antibiotics are presently being used industrially. (3)

In addition, there are assumptions that Chromobacterium violaceum strains seem to mine for gold from soil through the cyanide produced by bacterium. The produced cyanide reacts with gold to from a complex anion [Au(CN)2]- in which gold can be easily purified after the complex anion has dissociated in aqueous solution. (3)