Activity and viability of polycyclic aromatic hydrocarbon-degrading Sphingomonas sp. LB126 in a DC-electrical field typical for electrobioremediation measures

Abstract

There has been growing interest in employing electro-bioremediation, a hybrid technology of bioremediation and electrokinetics for the treatment of contaminated soil. Knowledge however on the effect of weak electrokinetic conditions on the activity and viability of pollutant-degrading microorganisms is scarce. Here we present data about the influence of direct current (DC) on the membrane integrity, adenosine triphosphate (ATP) pools, physico-chemical cell surface properties, degradation kinetics and culturability of fluorene-degrading Sphingomonas sp. LB126. Flow cytometry was applied to quantify the uptake of propidium iodide (PI) and the membrane potential-related fluorescence intensities (MPRFI) of individual cells within a population. Adenosine tri-phosphate contents and fluorene biodegradation rates of bulk cultures were determined and expressed on a per cell basis. The cells' surface hydrophobicity and electric charge were assessed by contact angle and zeta potential measurements respectively. Relative to the control, DC-exposed cells exhibited up to 60% elevated intracellular ATP levels and yet remained unaffected on all other levels of cellular integrity and functionality tested. Our data suggest that direct current (X=1 V cm(-1); J=10.2 mA cm(-2)) as typically used for electrobioremediation measures has no negative effect on the activity of the polycyclic aromatic hydrocarbon (PAH)-degrading soil microorganism, thereby filling a serious gap of the current knowledge of the electrobioremediation methodology.

Figure 1

Time‐dependent fractions of total (N_t; A) and PI‐stained (PI_t, B) Sphingomonas sp. LB126 cells in the presence (filled circles, 1 V cm⁻¹) and absence (open circles) of DC. Data are normalized relative to initial conditions (N_initial; PI_initial).

Figure 2

Normalized fractions of intracellular ATP contents (A) and cell membrane potential‐related fluorescence intensity (MPRFI) (B) in the presence (filled circles, 1 V cm⁻¹) and absence (open circles) of DC. Data are normalized relative to initial values.

Figure 3

Representation of the apparent fluorene biodegradation rates of Sphingomonas sp. LB126 relative to measured dissolved bulk fluorene concentrations in the presence (filled circles, 1 Vcm⁻¹) and absence (open circles) of DC. Fluorene biodegradation rates in the presence of DC were corrected for apparent abiotic (electrochemical) losses as described in Experimental procedures.

Figure 4

Time‐dependent physicochemical cell surface properties of Sphingomonas sp. LB126 exposed to DC. (A) and (B) reflect the water contact (θ_w) and the zeta potential (ζ), respectively, in the presence (filled circles, 1 V cm⁻¹) or absence (open circles) of DC.