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Applied and Environmental Microbiology, September 2004, p. 5569-5578, Vol. 70, No. 9
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.9.5569-5578.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Implicating the Glutathione-Gated Potassium Efflux System as a Cause of Electrophile-Induced Activated Sludge Deflocculation

Charles B. Bott and Nancy G. Love^*

The Charles E. Via, Jr., Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia

Received 10 January 2004/ Accepted 13 May 2004

The glutathione-gated K⁺ efflux (GGKE) system represents a protective microbial stress response that is activated by electrophilic or thiol-reactive stressors. It was hypothesized that efflux of cytoplasmic K⁺ occurs in activated sludge communities in response to shock loads of industrially relevant electrophilic chemicals and results in significant deflocculation. Novosphingobium capsulatum, a bacterium consistent with others found in activated sludge treatment systems, responded to electrophilic thiol reactants with rapid efflux of up to 80% of its cytoplasmic K⁺ pool. Furthermore, N. capsulatum and activated sludge cultures exhibited dynamic efflux-uptake-efflux responses very similar to those observed by others in Escherichia coli K-12 exposed to the electrophilic stressors N-ethylmaleimide and 1-chloro-2,4-dinitrobenzene and the reducing agent dithiothreitol. Fluorescent LIVE/DEAD stains were used to show that cell lysis was not the cause of electrophile-induced K⁺ efflux. Nigericin was used to artificially stimulate K⁺ efflux from N. capsulatum and activated sludge cultures as a comparison to electrophile-induced K⁺ efflux and showed that cytoplasmic K⁺ efflux by both means corresponded with activated sludge deflocculation. These results parallel those of previous studies with pure cultures in which GGKE was shown to cause cytoplasmic K⁺ efflux and implicate the GGKE system as a probable causal mechanism for electrophile-induced, activated sludge deflocculation. Calculations support the notion that shock loads of electrophilic chemicals result in very high K⁺ concentrations within the activated sludge floc structure, and these K⁺ levels are comparable to that which caused deflocculation by external (nonphysiological) KCl addition.

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* Corresponding author. Mailing address: The Charles E. Via, Jr., Department of Civil and Environmental Engineering, 418 Durham Hall, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0246. Phone: (540) 231-3980. Fax: (540) 231-7916. E-mail: nlove{at}vt.edu.

Present address: Department of Civil and Environmental Engineering, Virginia Military Institute, Lexington, VA 24450.

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Applied and Environmental Microbiology, September 2004, p. 5569-5578, Vol. 70, No. 9
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.9.5569-5578.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

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