Chromate Reduction in Shewanellaoneidensis MR‐1 Is an Inducible Process Associated with Anaerobic Growth

Abstract

Cr(VI) reduction was observed during tests with Shewanella oneidensis MR-1 (previously named S. putrefaciens MR-1) while being grown with nitrate or fumarate as electron acceptor and lactate as electron donor. From the onset of anoxic growth on fumarate, we measured a gradual and progressive increase in the specific Cr(VI) reduction rate with incubation time until a maximum was reached at late exponential/early stationary phase. Under denitrifying conditions, the specific Cr(VI) reduction rate was inhibited by nitrite, which is produced during nitrate reduction. However, once nitrite was consumed, the specific reduction rate increased until a maximum was reached, again during the late exponential/early stationary phase. Thus, under both fumarate- and nitrate-reducing conditions, an increase in the specific Cr(VI) reduction rate was observed as the microorganisms transition from oxic to anoxic growth conditions, presumably as a result of induction of enzyme systems capable of reducing Cr(VI). Although Cr(VI) reduction has been studied in MR-1 and in other facultative bacteria under both oxic and anoxic conditions, a transition in specific reduction rates based on physiological conditions during growth is a novel finding. Such physiological responses provide information required for optimizing the operation of in situ systems for remediating groundwater contaminated with heavy metals and radionuclides, especially those that are characterized by temporal variations in oxygen content. Moreover, such information may point the way to a better understanding of the cellular processes used by soil bacteria to accomplish Cr(VI) reduction.

Isolation of a High-Affinity Functional Protein Complex between OmcA and MtrC: Two Outer Membrane Decaheme c -Type Cytochromes of Shewanella oneidensis MR-1

“…Furthermore, to reduce insoluble metals such as Fe(III) and Mn(III/IV) at neutral pH in oxidizing environments, this network must be able to transfer electrons from the cytoplasmic membrane where electrons are generated to the extracellular surface of the outer membrane, where reduction is thought to occur (27). Identification of the proteins and their functions in mediating metal reduction is of considerable importance both from a standpoint of understanding bacterial physiology and in order to facilitate bioremediation of contaminated sites, since these metal-reducing activities may also function in the reduction and immobilization of toxic metals, including U(VI), Tc(VII), and Cr(VI) (25,(36)(37)(38)(39)(40).…”

Treatability Study of In Situ Technologies for Remediation of Hexavalent Chromium in Groundwater at the Puchack Well Field Superfund Site, New Jersey

“…However, the enzymatic reduction of Cr(VI) can occur under a wide range of redox conditions including in the presence of small amounts of oxygen. Reduction of Cr(VI) has been demonstrated under aerobic conditions (e.g., Bopp and Ehrlich 1988;Horitsu et al 1987;Ishibashi et al 1990), by dissimilatory iron reducing bacteria, DIRB (e.g., Caccavo et al 1992), under nitrate-or fumarate-reducing conditions (e.g., Viamajala et al 2002), and by sulfate-reducing bacteria (SRB) (e.g., Lovley and Phillips 1994).…”

Peer Reviewed: In-Situ Treatment of Chromium-Contaminated Groundwater

“…Direct enzymatic reduction can be achieved by two types of bacteria: dissimilatory metal-reducing bacteria that can use metals as electron acceptors for growth, or the fermentative and other anerobic metabolic groups that reduce metals, especially relatively easy-to-reduce metals like Cr(VI), as a byproduct of their primary metabolic activity. An example of a dissimilatory metal-reducing bacterium is Shewanella oneidensis, strain MR-1 (28). A fermentative bacterium that has been shown to reduce Cr(VI) is Enterobactor cloacae, strain HO1 (29).…”