Enhanced nitrate reduction and current generation by Bacillus sp. in the presence of iron oxides

Abstract

Purpose Fe(III) has been reported as a strictly competitive electron acceptor with respect to other substrate reductions by dissimilatory Fe(III)-reducing bacteria (DIRB). However, the effect of Fe(III) oxides on the substrate reduction by other microorganisms remain unknown. The aims of this study were to investigate the effects of iron oxides on the nitrate reduction and current generation by Bacillus sp., in which the nitrate and carbon anodes served as soluble and insoluble electron acceptors, respectively. Materials and methods Microbial nitrate reduction by Bacillus sp. were conducted in batch cultures in the absence or presence of four chemically synthesized iron(III) oxyhydroxides [i.e., α-FeOOH, γ-FeOOH, α-Fe 2 O 3 , and γ-Fe 2 O 3 ]. Anaerobic techniques were used throughout all the experiments. NO 3 − /NO 2 − was determined by ion chromatography, and NH 4 + was measured by spectrophotometry at 420 nm after a color reaction with Nessler's reagent. For total Fe(II) determination, samples were extracted using 0.5 M HCl and tested by spectrophotometry at 510 nm, and Fe(II) analyses in NO 3 − containing samples were performed using a sequential extraction technique. Current generation was tested using a bioelectrochemical reactor that consisted of two identical chambers separated by a cation exchange membrane. Results and discussionThe results showed that four iron oxides markedly enhanced the nitrate reduction and current generation by Bacillus sp. Nitrate reduction by the Fe(II) on the oxide surface was proven to take place, but with lower reduction rate than the direct microbial nitrate reduction by Bacillus sp. Al 2 O 3 and TiO 2 , as control without Fe(II) formation, also enhanced the nitrate reduction and current generation. It was proposed that the electron may be transferred from Bacillus sp. to conduction band of iron oxides to the nitrate or anode, according to their redox potential ranking as outer membrane enzyme of microorganisms < conduction band of iron oxides < electron acceptors. Conclusions This study demonstrated that the presence of iron oxides can obviously enhance both the nitrate reduction and current generation by Bacillus sp., which was in contrast to the previous report with respect to the inhibition effect of Fe(III) on substrate reduction by DIRB. With respect to the semiconductive properties of iron oxides, their roles during the nitrate reduction and current generation were speculated as a conduction band of iron oxides mediating the electron transfer from Bacillus sp. to the nitrate and anode.

Water quality assessment and source identification of the Shuangji River (China) using multivariate statistical methods

“…All samples were analysed within 48 hours. The COD was measured by the dichromate reflux method (DH310C1COD) [ 20 ], and NH 3 -N was measured with Nessler’s reagent (NH 3 N-1040) [ 21 ]. The TP was measured by ammonium molybdate spectrophotometry (HM-812) [ 22 ], and the CODMn was measured by the permanganate index method (Thermo Scientific 3131) [ 23 ].…”

Addition of iron oxides in sediments enhances 2,3,4,5-tetrachlorobiphenyl (PCB 61) dechlorination by low-voltage electric fields

“…In addition, it has been previously proposed that the semiconductor-mediated electron transfer might contribute to the enhanced reduction of electron acceptors (including the electrode and the pollutants with high redox potential) via the interconnected bacterial network, when the addition of iron oxides was effective in accelerating extracellular electron transfer rates. 48,49 This semiconductor-mediated mechanism might also be involved in electron transfer from the organic Fig. 4 Dependence of the rate constant of PCB 61 dechlorination on (a) the concentration of biogenic adsorbed Fe(II) and (b) the value of current.…”

Effects of exogenous short-chain N -acyl homoserine lactone on denitrifying process of Paracoccus denitrificans

“…The experiment was performed in triplicate and one-way analysis of variance (ANOVA) significance analysis was performed. ) concentrations were measured by anion chromatography method using ICS-1500 ion chromatography system (ICS-1500ICS, Dionex Corporation, America) (Zhang et al, 2012b). To obtain standard curves, NO 3 − -and NO 2 − -mixed standard stock solutions were diluted with ddH 2 O to reach concentrations of 0.2, 0.4, 0.6, 0.8, 1.0, 2.0, and 10.0 mg/L and 0.02, 0.04, 0.06, 0.08, 0.1, 0.2, and 1.0 mg/L, respectively.…”