''Shewanella'' is the sole genus included in the

marine bacteria Marine prokaryotes are marine bacteria and marine archaea. They are defined by their habitat as prokaryotes that live in marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. All cellular ...

family Shewanellaceae. Some species within it were formerly classed as ''

Alteromonas ''Alteromonas'' is a genus of Pseudomonadota found in sea water, either in the open ocean or in the coast. It is Gram-negative. Its cells are curved rods with a single polar flagellum. Etymology The etymology of the genus is Latin ''alter'' -' ...

''. ''Shewanella'' consists of facultatively anaerobic Gram-negative rods, most of which are found in extreme aquatic habitats where the temperature is very low and the pressure is very high. ''Shewanella'' bacteria are a normal component of the surface flora of fish and are implicated in fish spoilage. ''Shewanella chilikensis'', a species of the genus ''Shewanella'' commonly found in the marine sponges of Saint Martin's Island of the

Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line between ...

Bangladesh Bangladesh (}, ), officially the People's Republic of Bangladesh, is a country in South Asia. It is the eighth-most populous country in the world, with a population exceeding 165 million people in an area of . Bangladesh is among the mos ...

. ''Shewanella oneidensis'' MR-1 is a widely used laboratory model to study anaerobic respiration of metals and other anaerobic extracellular electron acceptors, and for teaching about microbial electrogenesis and

microbial fuel cells Microbial fuel cell (MFC) is a type of bioelectrochemical fuel cell system that generates electric current by diverting electrons produced from the microbial oxidation of reduced compounds (also known as fuel or electron donor) on the anode to ox ...

Biochemical characteristics of ''Shewanella'' species

Colony, morphological, physiological, and biochemical characteristics of ''Shewanella'' species are shown in the Table below. Note: + = Positive; – =Negative

Metabolism

Currently known ''Shewanella'' species are heterotrophic facultative anaerobes. In the absence of oxygen, members of this genus possess capabilities allowing the use of a variety of other electron acceptors for respiration. These include thiosulfate, sulfite, or elemental sulfur, as well as fumarate. Marine species have demonstrated an ability to use arsenic as an electron acceptor as well. Some members of this species, most notably ''Shewanella oneidensis'', have the ability to respire through a wide range of metal species, including manganese, chromium, uranium, and iron. Reduction of iron and manganese through ''Shewanella'' respiration has been shown to involve extracellular electron transfer through the employment of

bacterial nanowires Bacterial nanowires (also known as microbial nanowires) are electrically conductive appendages produced by a number of bacteria most notably from (but not exclusive to) the ''Geobacter'' and ''Shewanella'' genera. Conductive nanowires have also be ...

, extensions of the outer membrane.

Applications

The discovery of some of the respiratory capabilities possessed by members of this genus has opened the door to possible applications for these bacteria. The metal-reducing capabilities can potentially be applied to bioremediation of uranium-contaminated groundwater, with the reduced form of uranium produced being easier to remove from water than the more soluble uranium oxide. Scientists researching the creation of microbial fuel cells, designs that use bacteria to induce a current, have also made use of the metal reducing capabilities some species of ''Shewanella'' possess as a part of their metabolic repertoire.

Significance

One of the roles that the genus ''Shewanella'' has in the environment is

bioremediation Bioremediation broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi, and plants), living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluent ...

. ''Shewanella'' species have great metabolic versatility; they can reduce various electron acceptors. Some of the electron acceptors they use are toxic substances and heavy metals, which often become less toxic after being reduced. Examples of metals that ''Shewanella'' are capable of reducing and degrading include uranium, chromium, and iron. Its ability to decrease toxicity of various substances makes ''Shewanella'' a useful tool for bioremediation. Specifically, ''

Shewanella oneidensis ''Shewanella oneidensis'' is a bacterium notable for its ability to reduce metal ions and live in environments with or without oxygen. This proteobacterium was first isolated from Lake Oneida, NY in 1988, hence its name. ''S. oneidensis'' is a ...

'' strain MR-1 is often used to clean up contaminated nuclear weapon manufacturing sites. ''Shewanella'' also contributes to the biogeochemical circulation of minerals. Members of this genus are widely distributed in aquatic habitats, from the deep sea to the shallow Antarctic Ocean. Its diverse habitats, coupled to its ability to reduce a variety of metals, makes the genus critical for the cycling of minerals. For instance, under aerobic conditions, various species of ''Shewanella''are capable of oxidizing manganese. When conditions are changed, the same species can reduce the manganese oxide products. Hence, since ''Shewanella'' can both oxidize and reduce manganese, it is critical to the cycling of manganese.

References

External links

List of bacterial genera named after personal names Many bacterial species are named after people, either the discoverer or a famous person in the field of microbiology. For example, ''Salmonella'' is named after D.E. Salmon, who discovered it (albeit as "''Bacillus typhi''"). For the generic epit ...