Shewanella are facultatively anaerobic, Gram-negative bacteria, motile by polar flagella, rod-like, and generally associated with aquatic or marine environments. . They are capable of using a variety of compounds as electron acceptors, including oxygen, iron, manganese, uranium, nitrate, nitrite, fumarate, to name but a few. This ability makes Shewanella important for bioremediation of contaminated metals and radioactive wastes. The genus Shewanella comprises 36 recognized and hundreds of uncharacterized cultivable species.

A denitrifying estuarine bacteria, Shewanella denitrificans was isolated from the oxic--anoxic interface of an anoxic basin of the central Baltic Sea. It is an unpigmented, polarly flagellated, mesophilic, facultatively anaerobic bacterium, able to use nitrate, nitrite and sulphite as electron acceptors. Strain OS217 is the type strain. It grows optimally at 20-25 degrees Celsius, and in 1-3% salt (NaCl).