A Facultative Electroactive Chromium(VI)-Reducing Bacterium Aerobically Isolated From a Biocathode Microbial Fuel Cell

Abstract

A facultative electroactive bacterium, designated strain H, was aerobically isolated from the biocathode of a hexavalent chromium (Cr(VI))-reducing microbial fuel cell (MFC). Strain H is Gram-positive and rod shaped (1–3 μm length). 16S rRNA gene analysis suggested that this strain (accession number MH782060) belongs to the genus Bacillus and shows maximum similarity to Bacillus cereus whose electrochemical activity has never previously been reported. Moreover, this strain showed efficient Cr(VI)-reducing ability in both heterotrophic (aerobic LB broth) and autotrophic (anaerobic MFC cathode) environments. Cr(VI) removal reached 50.6 ± 1.8% after 20 h in LB broth supplemented with Cr(VI) (40 mg/L). The strain H biocathode significantly improved the performance of the Cr(VI)-reducing MFC, achieving a maximum power density of 31.80 ± 1.06 mW/m2 and Cr(VI) removal rate of 2.56 ± 0.10 mg/L–h, which were 1.26 and 1.75 times higher than those of the MFC with the sterile control cathode, respectively. This study offers a novel Gram-positive Bacillus sp. strain for Cr(VI) removal in MFCs, and shows a facile aerobic isolation method could be used to screen facultative electroactive bacteria.

Synchronous Cr(VI) Remediation and Energy Production Using Microbial Fuel Cell from a Subsurface Environment: A Review

“…The most important characteristic of abiotic cathodes is the conduction of electrons that are produced from the oxidization of organic matter by anodic microorganisms through the electrode surface [46], which achieved the conversion from chemical energy to electric energy as well as the simultaneous removal of Cr(VI). By summarizing previous results, we draw the abiotic cathode mechanism in Figure 3a [16,42,47]. However, the traditional MFC with abiotic cathode has some problems such as difficult chemical regeneration, demand for platinum and other precious metals catalysts, as well as a high cost.…”

“…Moreover, the accumulated bacteria can promote electron transfer and decrease the charge transfer resistance [49], along with increasing reduction efficiency. Biological cathode uses microorganisms as the catalyst to transfer electrons towards the electron acceptor through an external circuit [21] and By summarizing previous results, its mechanism is shown in Figure 3b [16,42,47]. Tandukar et al [16] used a biological cathode MFC for the first time for Cr(VI) remediation.…”

Progress Towards Bioelectrochemical Remediation of Hexavalent Chromium

“…The combined use of the electrode and lactate as electron donors allowed bio-electrochemical and non-bio-electrochemical Cr(VI) reduction at the same time, even the contribution of the two different mechanisms to the overall process was not recognized. In Wu et al [102], Bacillus sp. showed efficient Cr(VI)-reducing ability in both heterotrophic and autotrophic environments.…”

“…Anaerobic pure cultures were also tested [91,92,102]. Hsu et al [91] compared Cr(VI) reduction by six Shewanella strains at the cathode of MFCs in repeated cycles, observing initially the use of the electrode as the sole electron source in all tested strains.…”

Three-Stage Single-Chambered Microbial Fuel Cell Biosensor Inoculated with Exiguobacterium aestuarii YC211 for Continuous Chromium (VI) Measurement

“…MFCs involving Cr(VI) have been developed for different purposes. In the cathode of an MFC, Cr(VI) is used as an electron acceptor to be reduced or removed [18], to facilitate electricity production [19], or to detect trace Cr(VI) concentrations of 0.2–0.7 mg/L [20] in batch mode. In the anode of an MFC, Cr(VI) may be used as a toxic compound to cause the voltage to drop in the MFC because of the inhibition of anodic electrogenic bacteria activity.…”