''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 cellu ...

family Shewanellaceae. Some species within it were formerly classed as '' Alteromonas''. ''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 Saint Martin's Island () is a small coral island in the north-eastern part of the Bay of Bengal, about 9 km south of the tip of the Cox's Bazar-Teknaf peninsula, and forms the southernmost part of Bangladesh. It has an area of only 3 ...

of the

Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean. Geographically it is positioned between the Indian subcontinent and the Mainland Southeast Asia, Indochinese peninsula, located below the Bengal region. Many South Asian and Southe ...

Bangladesh Bangladesh, officially the People's Republic of Bangladesh, is a country in South Asia. It is the List of countries and dependencies by population, eighth-most populous country in the world and among the List of countries and dependencies by ...

. ''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 Electroreception and electrogenesis are the closely related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes, such ...

and

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

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 A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

facultative anaerobes A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent. Some examples of facultatively anaerobic bacteria are ''Staphylococcus' ...

. 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 the ''Geobacter'' and '' Shewanella'' genera. Conductive nanowires have also been reported in the oxy ...

, 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 Bioremediation broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi in mycoremediation, and plants in phytoremediation), living or dead, is employed for removing environmental pollutants from air, wate ...

of uranium-contaminated groundwater, with the reduced form of uranium produced being easier to remove from water than the more soluble

uranium oxide Uranium oxide is an oxide of the element uranium. The metal uranium forms several oxides: * Uranium dioxide or uranium(IV) oxide (UO2, the mineral uraninite or pitchblende) * Diuranium pentoxide or uranium(V) oxide (U2O5) * Uranium trioxide or ...

. 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

. ''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. ''Shewanella oneidensi ...

'' 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