Cr(VI) reduction and Cr(III) immobilization by resting cells of Pseudomonas aeruginosa CCTCC AB93066: spectroscopic, microscopic, and mass balance analysis

Abstract

The aim of this study was to investigate the mechanism of Cr(VI) reduction and Cr(III) immobilization by resting cells of Pseudomonas aeruginosa using batch experiments and analysis techniques. Data showed that resting cells of this strain (3.2 g/L dry weight) reduced 10 mg/L of Cr(VI) by 86% in Tris-HCl buffer solution under optimized conditions of 5 g/L of sodium acetate as an electron donor, pH of 7.0 and temperature of 37 °C within 24 h. Cr(VI) was largely converted to nontoxic Cr(III), and both soluble crude cell-free extracts and membrane-associated fractions were responsible for Cr(VI) reduction. While remnant Cr(VI) existed only in the supernatant, the content of resultant Cr(III) in supernatant, on cell surface and inside cells was 2.62, 1.06, and 5.07 mg/L, respectively, which was an indicative of extracellular and intracellular reduction of chromate. Scanning electron microscopy analysis combined with energy dispersive X-ray spectroscopy revealed the adsorption of chromium on the bacterial surface. Interaction between Cr(III) and cell surface functional groups immobilized Cr(III) as indicated by Fourier transform infrared analyses and X-ray photoelectron spectroscopy. Transmission electron microscopy revealed Cr(III) precipitates in bacterial interior suggesting that Cr(II) could also be intracellularly accumulated. Thus, it can be concluded that interior and exterior surfaces of resting P. aeruginosa cells were sites for reduction and immobilization of Cr(VI) and Cr(III), respectively. This is further insight into the underlying mechanisms of microbial chromate reduction.

Operational Characteristics of Immobilized Ochrobactrum sp. CUST210-1 Biosystem and Immobilized Chromate Reductase Biosystem in Continuously Treating Actual Chromium-Containing Wastewater

“…(1) Partial Cr(VI) directly binds via electrostatic attraction to positively charged functional groups on the surface of the CUST210-1 strain (3.05%), or partial Cr(VI) is reduced to Cr(III) via membrane-associated chromate reductase or soluble chromate reductase (i.e., ChrR) and binds to negatively charged functional groups on the surface of the CUST210-1 strain (8.49%), ( 2 ). An analogous mechanism has been discovered in other bacteria, such as P. aeruginosa and S. maltophilia [14,36].…”

“…To consider the characteristics of Cr(VI)-containing wastewater and the operational performance of the biosystem, the pH value of the experiment was controlled at 7.0. An optimal Cr(VI) reduction at pH 7.0 was determined for Bacillus sp., P. aeruginosa, and S. maltophilia [14,36,41]. The decrease in Cr(VI) reduction efficiency at pH 9.0 was mainly attributed to the possibility that deviation from appropriate pH values may affect the degree of ionization of ChrR [36].…”

Reduction of hexavalent chromium (VI) by indigenous alkaliphilic and halotolerantMicrobacteriumsp. M5: comparative studies under growth and nongrowth conditions

“…Furthermore, Cr (VI) reduction potential of cells under nongrowth conditions was evaluated to explore possibility for field scale. In earlier studies resting cells of P. aeruginosa CCTCC AB93066 were able to achieve 86% reduction of 10 mg l −1 of Cr (VI) in Tris‐HCl buffer solution under optimized conditions (Kang et al ) whereas Pseudomonas brassicacearum LZ‐4 cells could reduce 80% of 10 mg l −1 of Cr (VI) (Yu et al ). Recently Zeng et al () reported a novel culture Oceanobacillus oncorhynchi W4 which was able to reduce 80% of 10 mg l −1 Cr (VI) under resting cell conditions in Tris‐HCl buffer after 24 h. In this study, the resting cells of isolate M5 could tolerate five time higher concentration of Cr (VI) than reported in previous studies and afforded to reduce 22·71 ± 0·5% of 50 mg l −1 Cr (VI) in 50 mmol l −1 Tris‐HCl buffer after 20 h.…”

Three-Stage Single-Chambered Microbial Fuel Cell Biosensor Inoculated with Exiguobacterium aestuarii YC211 for Continuous Chromium (VI) Measurement

“…To date, various bacterial strains, including Pseudomonas sp., Enterobacter aerogenes , Serratia proteamaculans , Bacillus sp., Microbacterium sp., Trichococcus pasteurii , Desulfovibrio vulgaris , Ochrobactrum sp., Escherichia coli , Shewanella algae , Paenibacillus ferrarius , Exiguobacterium aestuarii , and Stenotrophomonas maltophilia , capable of reducing Cr(VI) to Cr(III), have been isolated from various environments under anaerobic or aerobic conditions [3,4,5,6,7,8,9]. Although most of these microbes have been isolated, the availability of high selectivity, high reducing power, broad environmental tolerance, and anaerobic Cr(VI)-reducing bacteria is a prerequisite for accurate Cr(VI) measurement from actual wastewater using microbial fuel cells (MFCs).…”