Toxicity of Cr(lll) to Shewanella sp. strain MR-4 during Cr(VI) reduction.

Bioremediation of chromium through the reduction of hexavalent chromium (as the chromate ion, CrO42-) is based on the notion that the product, trivalent chromium (Cr(III)), is less toxic than chromate. In this study, we show that soluble Cr(III), present at pH 6-8 as the Cr3+ ion and/or hydroxyl complexes (henceforth referred to as uncomplexed Cr(III)), can be found transiently in significant concentrations and has a deleterious effect on Shewanella sp. MR-4.

Global transcriptional profiling of Shewanella oneidensis MR-1 during Cr(VI) and U(VI) reduction.

Whole-genome DNA microarrays were used to examine the gene expression profile of Shewanella oneidensis MR-1 during U(VI) and Cr(VI) reduction. The same control, cells pregrown with nitrate and incubated with no electron acceptor, was used for the two time points considered and for both metals. U(VI)-reducing conditions resulted in the upregulation (> or = 3-fold) of 121 genes, while 83 genes were upregulated under Cr(VI)-reducing conditions.

Chemical speciation and toxicity of metals assessed by three bioluminescence-based assays using marine organisms.

Metal toxicity is a function of the biology of the target organism and the chemical speciation of the metal. The toxicity of 11 metals was assessed with three cell-based bioassays based on marine organisms: the bacterium Photobacterium phosphoreum of the Microtox bioassay, an environmental strain of P. phosphoreum, and photocytes isolated from the brittlestar Ophiopsila californica.

Fate of uranyl in a quaternary system composed of uranyl, citrate, goethite, and Pseudomonas fluorescens.

This study investigated the partitioning of uranyl within a quaternary system made up of uranyl, citrate, goethite, and the bacterium Pseudomonas fluorescens. In the absence of cells, uranyl was sorbed to goethite as a complex involving surface groups and/or citrate. Measurements of the evolution of CO2 indicated that the addition of bacterial cells lead to the gradual biodegradation of citrate.

Cometabolism of Cr(VI) by Shewanella oneidensis MR-1 produces cell-associated reduced chromium and inhibits growth.

Microbial reduction is a promising strategy for chromium remediation, but the effects of competing electron acceptors are still poorly understood. We investigated chromate (Cr(VI)) reduction in batch cultures of Shewanella oneidensis MR-1 under aerobic and denitrifying conditions and in the absence of an additional electron acceptor. Growth and Cr(VI) removal patterns suggested a cometabolic reduction; in the absence of nitrate or oxygen, MR-1 reduced Cr(VI), but without any increase in viable cell counts and rates gradually decreased when cells were respiked.