title: Marine phototrophic consortia transfer electrons to electrodes in response to reductive stress.
abstract: This work studies how extracellular electron transfer (EET) from cyanobacteria-dominated marine microbial biofilms to solid electrodes is affected by the availability of inorganic carbon (Ci). The EET was recorded chronoamperometrically in the form of electrical current by a potentiostat in two identical photo-electrochemical cells using carbon electrodes poised at a potential of +0.6 V versus standard hydrogen electrode under 12/12 h illumination/dark cycles. The Ci was supplied by the addition of NaHCO3 to the medium and/or by sparging CO2 gas. At high Ci conditions, EET from the microbial biofilm to the electrodes was observed only during the dark phase, indicating the occurrence of a form of night-time respiration that can use insoluble electrodes as the terminal electron acceptor. At low or no Ci conditions, however, EET also occurred during illumination suggesting that, in the absence of their natural electron acceptor, some cyanobacteria are able to utilise solid electrodes as an electron sink. This may be a natural survival mechanism for cyanobacteria to maintain redox balance in environments with limiting CO2 and/or high light intensity.
authors.affiliation: Advanced Water Management Centre, The University of Queensland, St. Lucia, QLD, 4072, Australia.
authors.forename: Libertus
authors.initials: L
authors.lastname: Darus
authors.affiliation: Advanced Water Management Centre, The University of Queensland, St. Lucia, QLD, 4072, Australia.
authors.forename: Pablo
authors.initials: P
authors.lastname: Ledezma
authors.affiliation: Advanced Water Management Centre, The University of Queensland, St. Lucia, QLD, 4072, Australia.
authors.forename: Jürg
authors.initials: J
authors.lastname: Keller
authors.affiliation: Advanced Water Management Centre, The University of Queensland, St. Lucia, QLD, 4072, Australia. s.freguia@uq.edu.au.
authors.forename: Stefano
authors.identifier: http://orcid.org/0000-0002-2294-9036
authors.initials: S
authors.lastname: Freguia
mesh_terms: D059001:Aquatic Organisms / Q000502:physiology* / Q000528:radiation effects*; D002244:Carbon / Q000378:metabolism; D019069:Cell Respiration; D004275:DNA, Ribosomal / Q000235:genetics; D004560:Electricity; D004566:Electrodes; D004583:Electrons; D008027:Light; D059013:Microbial Consortia / Q000528:radiation effects; D009930:Organic Chemicals / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D052817:Phototrophic Processes / Q000528:radiation effects; D017422:Sequence Analysis, DNA; D013312:Stress, Physiological / Q000528:radiation effects*
chemical_list: D004275:DNA, Ribosomal; D009930:Organic Chemicals; D002244:Carbon; D010100:Oxygen
keywords: Biophotovoltaics; Cyanobacteria; Excess electron dissipation; Extracellular electron transfer; Marine photosynthetic bacteria; Microbial solar cell