Shewanella oneidensis is a bacterium notable for its ability to reduce metal ions and live in environments with or without oxygen.

The special interest in S. oneidensis MR-1 revolves around its behavior in an anaerobic environment contaminated by heavy metals such as iron, lead and uranium.

It is a common misconception to think that MR-1 refers to "metal-reducing" instead of the original intended "manganese-reducing" as observed by Kenneth H. Nealson, who first isolated the organism.

Although it was originally known as "manganese-reducing", the additional abbreviation expansion of "metal-reducing" is also valid as S. oneidensis MR-1 does reduce metals other than manganese.

This process of producing an external filament is completely absent from conventional bacterial respiration and is the center of many current studies.

Putative multidrug efflux transporters, detoxification proteins, extracytoplasmic sigma factors and PAS domain regulators are shown to have higher expression activity in presence of heavy metal.

[3] In contrast to chemical and physical methods, microbial processes for synthesizing nanomaterials can be achieved in aqueous phase under gentle and environmentally benign conditions.

[12] A 2013 study suggested that it is possible to alter particle size and activity of extracellular biogenic nanoparticles via controlled expression of the genes encoding surface proteins.

An important example is the synthesis of silver nanoparticle by S. oneidensis, where its antibacterial activity can be influenced by the expression of outer membrane c-type cytochromes.

Shewanella oneidensis' ability to reduce and absorb heavy metals makes it a candidate for use in wastewater treatment.