Implicating the glutathione-gated potassium efflux system as a cause of electrophile-induced activated sludge deflocculation.
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.
Bott
Charles B
CB
Department of Civil and Environmental Engineering, 418 Durham Hall, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0246, USA.
Love
Nancy G
NG
D005427:Flocculation; D005978:Glutathione / Q000378:metabolism*; D007700:Kinetics; D009550:Nigericin / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012722:Sewage / Q000382:microbiology*; D042301:Sphingomonadaceae / Q000187:drug effects / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism*
D012722:Sewage; D005978:Glutathione; D009550:Nigericin; D011188:Potassium