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

Abstract

ABSTRACT 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.