Chromium(VI) Bioremoval by Pseudomonas Bacteria: Role of Microbial Exudates for Natural Attenuation and Biotreatment of Cr(VI) Contamination

Abstract

Laboratory batch and column experiments were conducted to investigate the role of microbial exudates, e.g., exopolymeric substance (EPS) and alginic acid, on microbial Cr(VI) reduction by two different Pseudomonas strains (P. putida P18 and P. aeuroginosa P16) as a method for treating subsurface environment contaminated with Cr(VI). Our results indicate that microbial exudates significantly enhanced microbial Cr(VI) reduction rates by forming less toxic and highly soluble organo-Cr(III) complexes despite the fact Cr(III) has a very low solubility under the experimental conditions studied (e.g., pH 7). The formation of soluble organo-Cr(III) complexes led to the protection of the cells and chromate reductases from inactivation. In systems with no organic ligands, soluble organo-Cr(III) end products were formed between Cr(III) and the EPS directly released by bacteria due to cell lysis. Our results also provide evidence that cell lysis played an important role in microbial Cr(VI) reduction by Pseudomonas bacteria due to the release of constitutive reductases that intracellularly and/or extracellularly catalyzed the reduction of Cr(VI) to Cr(III). The overall results highlight the need for incorporation of the release and formation of organo-Cr(III) complexes into reactive transport models to more accurately design and monitor in situ microbial remediation techniques for the treatment of subsurface systems contaminated with Cr(VI).

Determination of the accumulation, spatial distribution and reduction of Cr in unsaturated Pseudochrobactrum saccharolyticum LY10 biofilms by X-ray fluorescence and absorption methods

“…Several bacterial strains with the ability to reduce Cr(VI) to Cr(III) aerobically or anaerobically have been isolated, and these include Pseudomonas aeruginosa, Ochrobactrum anthropic, Pseudmonas putida etc. [7][8][9]. In our previous study, a Cr(VI)-reducing bacterium named Pseudochrobactrum saccharolyticum LY10 was isolated and characterized to have a high Cr(VI)-reducing ability, alkali-tolerance and halo-tolerance [6].…”

Enzymatic Chromium (VI) Reduction by Cytoplasmic and Cell Membrane Fractions of Chromate-Reducing Bacterium Isolated From Sewage Treatment Plant

“…However, a number of recent studies suggest that Cr (VI) reduction by some bacteria strains such as Pseudomonas (Dogan et al, 2011) and Bacillus sp. (Desai et al, 2008a) led to the production of soluble Cr (III) end products instead of Cr (OH) 3 .…”

Electron Microscopy and X-ray Analysis of Cr-Containing Precipitates Synthesized by Newly Isolated Actinobacterium, Flexivirga alba ST13T

“…Electron microscopic observations of Cr precipitation using Cr(VI)-reducing bacteria have shown the usefulness of those bacteria for the detoxification of Cr(VI)-contaminated environment [6][7][8][9]. However we and others result need more investigations to establish a method for an efficient precipitation of Cr(III) synthesized by Cr(VI)-reducing bacterium.…”