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Front. Microbiol. | doi: 10.3389/fmicb.2018.00349

Petrophilic, Fe(III) reducing exoelectrogen Citrobacter sp. KVM11, isolated from hydrocarbon fed microbial electrochemical remediation systems

  • 1Centre for Environmental Risk Assessment and Remediation (CERAR), University of South Australia, Australia
  • 2CRC for Contamination Assessment and Remediation of the Environment (CRCCARE), Mawson Lakes, South Australia 5095, Australia, Australia
  • 3Division of Sustainable Development, Hamad bin Khalifa University, Qatar
  • 4Global Centre for Environmental Remediation (GCER), The University of Newcastle, Callaghan, NSW, Australia

Exoelectrogenic biofilms capable of extracellular electron transfer are important in advanced technologies such as those used in microbial electrochemical remediation systems (MERS) Few bacterial strains have been, nevertheless, obtained from MERS exoelectrogenic biofilms and characterised for bioremediation potential. Here we report the identification of one such bacterial strain, Citrobacter sp. KVM11, a petrophilic, iron reducing bacterial strain isolated from hydrocarbon fed MERS, producing anodic currents in microbial electrochemical systems. Fe(III) reduction of 90.01±0.43% was observed during five weeks of incubation with Fe(III) supplemented liquid cultures. Biodegradation screening assays showed that the hydrocarbon degradation had been carried out by metabolically active cells accompanied by growth. The characteristic feature of diazo dye decolorization was used as a simple criterion for evaluating the electrochemical activity in the candidate microbe. The electrochemical activities of the strain KVM11 were characterized in a single chamber fuel cell and three electrode electrochemical cells. The inoculation of strain KVM11 amended with acetate and citrate as the sole carbon and energy sources has resulted in an increase in anodic currents (maximum current density) of 212 ± 3 and 359 ± mA/m2 with respective coulombic efficiencies of 19.5% and 34.9% in a single chamber fuel cells. Cyclic voltammetry studies showed that anaerobically grown cells of strain KVM11 are electrochemically active whereas aerobically grown cells lacked the electrochemical activity. Electrobioremediation potential of the strain KVM11 was investigated in hydrocarbonoclastic and dye detoxification conditions using MERS. About 89.60% of 400 mg l-1 azo dye was removed during the first 24 h of operation and it reached below detection limits by the end of the batch operation (60 h). Current generation and biodegradation capabilities of strain KVM11 were examined using an initial concentration of 800 mg l-1 of diesel range hydrocarbons (C9-C36) in MERS (maximum current density 50.64 ±7 mA/m2 ; power density 4.08± 2 mW/m2, 1000Ω, hydrocarbon removal 60.14 ± 0.7%). Such observations reveal the potential of electroactive biofilms in the simultaneous remediation of hydrocarbon contaminated environments with generation of energy

Keywords: Electroactive biofilms, Citrobacter sp. KVM11, iron reducing, petrophilic, extracellular electron flow, microbial electrochemical remediation systems, hydrocarbonoclastic potential

Received: 21 Feb 2017; Accepted: 14 Feb 2018.

Edited by:

Yong Xiao, Institute of Urban Environment (CAS), China

Reviewed by:

Baogang Zhang, China University of Geosciences, China
Gefu Zhu, Institute of Urban Environment (CAS), China  

Copyright: © 2018 Venkidusamy, Rao and Mallavarapu. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Krishnaveni Venkidusamy, University of South Australia, Centre for Environmental Risk Assessment and Remediation (CERAR), Adelaide, Australia, krishnaveni.venkidusamy@mymail.unisa.edu.au