Higher order taxa
Bacteria; Proteobacteria; Gammaproteobacteria; Enterobacteriales; Enterobacteriaceae; Enterobacter
Description and significance
Enterobacter asburiae is a metabolically versatile and potentially useful bacteria; it has been shown to be mostly detrimental to humans. However, it has other properties that make it beneficial to human society. It has been known to colonize the human body, causing disease such as necrotizing fasciitis . Some research on how E. asburiae can both degrade polyethylene plastics  and to introduce early disease fighting enzymes to plants (which helps prevent agricultural decay)  has also been done. E. asburiae are also versatile in the nutrients they can metabolize, freeing up phosphorus and other minerals for plants . With more research and possible subsequent applications, E. asburiae may prove to be very useful to human society and the environment, especially taking into consideration their ability to degrade polyethylene plastics.
The whole genome of Enterobacter asburiae is found to be between 4.5 and 4.65 Mb [2,12]. It is found to contain 4,790 protein-coding genes, 87 tRNA genes, and 25 rRNA genes organized into 8 rRNA operons.
Additionally, E. asburiae is genetically related to other Enterobacter species, most closely with Enterobacter cloacae (63% genetic similarity) . It is also relatively closely related (40 to 53% genetic similarity) to other Enterobacter species including E. dissolvens, E. taylorae, and E. agglomerans to name a few .
Cell structure and Metabolism
Enterobacter asburiae belongs to the Enterobacteriaceae family, which are Gram-negative, non-spore forming, rod-shaped bacteria . E. asburiae is about 1.5 micrometers in length . Enterobacter are oxidase-negative as well as indole-negative and urease-negative . The family enterobacteriaceae are facultatively anaerobic organisms, allowing them to use oxygen as an ATP source when available, but can also produce energy without it . The genus Enterobacter ferments lactose with gas production at 37 degrees celsius, during a 48 hour period, in the presence of detergents and bile salts . E. asburiae is also known for being able to break down carcinogens and toxins, notably malachite green, into products that are not harmful .
Ecology and Pathology
Enterobacter asburiae consists of 71 different strains. 70 of these strains can be directly isolated from the human microbiome . In humans, E. asburiae can be present in many different microbe environments. Sources include urine, stools, wounds, and blood . In addition to humans, it can dwell inside many plant species and can be influential in helping these plant species to start making early disease fighting enzymes . Generally, E. asburiae is widely distributed across the United States so it is easy to come into contact with it.
It has been documented that Enterobacter asburiae can cause a variety of diseases in humans . It is however, generally an opportunistic pathogen and does not pose a significant threat to humans . Common conditions include necrotizing fasciitis, a condition that causes death of certain tissues, and can also cause infections in open wounds . A joint study done by doctors at the Department of Orthopedics and the Trauma Services Center in Ohio revealed that E. asburiae, in combination with another bacterial species, A. hydrophila, cause these open wound infections. Symptoms of infection usually include unusually high fevers, chills, nausea, a general feeling of being weak, and pain in the infected area due to the necrotizing skin. If open wounds are infected, the area around it can start to release pus. In most cases, it can be subsided via treatment with antibiotics . E. asburiae is generally an opportunistic pathogen and does not pose a significant threat to humans .
Enterobacter asburiae has a wide range of applications, from aiding in plant growth to degrading polyethylene. One way in which Enterobacter asburiae is able to protect plant growth is by plant disease suppression. With the introduction of lipopolysaccharides from the bacteria it has been demonstrated that the activity of early-disease fighting enzymes is substantially increased . Along with that, plants introduced to the lipopolysaccharides of the RS83 strain of this bacteria exhibited 90 percent less disease than plants with no exposure . Future use of this bacteria in agricultural techniques may prevent crop rotting.
The bacteria also inhibits metal accumulation in plants such as soybeans (zinc and copper), that can be toxic to their growth . Introduction of certain strains of Enterobacter asburiae can prevent these metals from stressing the plants, while simultaneously increasing nutrient uptake . Lastly, it has been found that Enterobacter asburiae produces ectophosphase, an enzyme that helps solubilize mineral phosphates in soil . This allows nutrients to be gained from other sources, freeing up more nutrients for the plants by making use of its structure and its membrane bound proteins. Thus, although initial research showed this bacteria to be mostly pathogenic, subsequent research has shown that it possesses a lot of benefits as well.
Another notable property of E. asburiae is its ability to degrade polyethylene. Polyethylene is the most common plastic and has long been classified as one of the main pollutants of the planet. Enterobacter asburiae is found in the gut of worms dubbed plastic-eating worms. In fact, this bacteria is the main contributor to the ability of these worms to break down polyethylene. Research in this particular area has been limited, but could offer a solution to the growing problem of increased plastic deposition on the planet. Enterobacter asburiae works alongside other bacteria in the gut of these worms to break down the plastic, similar to the gut bacteria found in humans . This discovery offers another benefit by E. asburiae and can help to limit the expansion of plastic waste in the future.
A study showed that E. asburiae could break down malachite green. Malachite green is an industrial dye used worldwide, but has been known to be a carcinogen to many organisms, including humans . The study concludes that a particular strain of E. absuriae called XJUHX-4TM was capable of breaking down malachite green up to a concentration of 1000 mg/L. Enzymes involved in the breakdown included laccase and malachite green reductase. Further analysis of the breakdown products revealed their non-mutagenic and non-carcinogenic nature .
Diamondback moth symbiosis
A study done on Diamondback moths found that E. absuriae is present in the gut of this organism in a symbiotic relationship with the moth. These moths are considered major pests and have been shown to be resistant to various insecticides. The study focused on a particular type of chemical used as an insecticide called acephate. Diamond-back moths are resistant to acephate, and the reason may be because E. absuriae can break down acephate and use it as a carbon and a nitrogen source .
Primary Biliary Cirrhosis
In patients suffering from primary biliary cirrhosis, the bile ducts of the liver become damaged and causes the build up of bile and various other toxins, that over time, damages the liver. A study done on 42 patients suffering from PBC focused on the gut microbiome of these patients compared to healthy controls . It was found that the gut microbiome of PBC patients was missing some key bacteria beneficial to humans, like Ruminococcus bromii, and instead, their guts were colonized by lots of opportunistic pathogens, like Klebsiella and E. absuriae . Thus, PBC can be attributed, at least to some extent, the colonization of the gut microbiome by opportunistic pathogens like E. absuriae.
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Edited by [Prateem Naini, Dorian Rutherford, Sheen Syal, and Grant Wagner], students of Jennifer Talbot for [www.bu.edu/academics/courses/cas/cas-bi-311/ BI 311 General Microbiology], 2016, [http:// ww.bu.edu/ Boston University].