Gonzalez-Aravena A C, Yunus K, Zhang L, Norling B, Fisher A C
Department of Chemical Engineering and Biotechnology, University of Cambridge Philippa Fawcett Drive Cambridge CB3 0AS UK
School of Biological Sciences, Nanyang Technological University 637551 Singapore.
RSC Adv. 2018 Jun 4;8(36):20263-20274. doi: 10.1039/c8ra00951a. eCollection 2018 May 30.
The exoelectrogenic capacity of the cyanobacterium PCC7942 was studied in iron limited growth in order to establish conditions favouring extracellular electron transfer in cyanobacteria for photo-bioelectricity generation. Investigation into extracellular reduction of ferricyanide by PCC7942 demonstrated enhanced capability for the iron limited conditions in comparison to the iron sufficient conditions. Furtheremore, the significance of pH showed that higher rates of ferricyanide reduction occurred at pH 7, with a 2.7-fold increase with respect to pH 9.5 for iron sufficient cultures and 24-fold increase for iron limited cultures. The strategy presented induced exoelectrogenesis driven mainly by photosynthesis and an estimated redirection of the 28% of electrons from photosynthetic activity was achieved by the iron limited conditions. In addition, ferricyanide reduction in the dark by iron limited cultures also presented a significant improvement, with a 6-fold increase in comparison to iron sufficient cultures. PCC7942 ferricyanide reduction rates are unprecedented for cyanobacteria and they are comparable to those of microalgae. The redox activity of biofilms directly on ITO-coated glass, in the absence of any artificial mediator, was also enhanced under the iron limited conditions, implying that iron limitation increased exoelectrogenesis at the outer membrane level. Cyclic voltammetry of PCC7942 biofilms on ITO-coated glass showed a midpoint potential around 0.22 V Ag/AgCl and iron limited biofilms had the capability to sustain currents in a saturated-like fashion. The present work proposes an iron related exoelectrogenic capacity of PCC7942 and sets a starting point for the study of this strain in order to improve photo-bioelectricity and dark-bioelectricity generation by cyanobacteria, including more sustainable mediatorless systems.
为了确定有利于蓝藻细胞外电子转移以用于光生物发电的条件，研究了蓝藻PCC7942在铁限制生长条件下的产电能力。对PCC7942细胞外还原铁氰化物的研究表明，与铁充足条件相比，铁限制条件下其还原能力增强。此外，pH值的影响表明，在pH 7时铁氰化物还原速率更高，铁充足培养物在pH 7时的还原速率相对于pH 9.5增加了2.7倍，铁限制培养物则增加了24倍。所提出的策略诱导了主要由光合作用驱动的产电过程，并且铁限制条件实现了约28%的光合电子的重新定向。此外，铁限制培养物在黑暗中对铁氰化物的还原也有显著改善，与铁充足培养物相比增加了6倍。PCC7942的铁氰化物还原速率在蓝藻中是前所未有的，与微藻相当。在没有任何人工介质的情况下，铁限制条件下直接在涂有ITO的玻璃上的生物膜的氧化还原活性也增强了，这意味着铁限制增加了外膜水平的产电。涂有ITO的玻璃上PCC7942生物膜的循环伏安法显示中点电位约为0.22 V Ag/AgCl，铁限制生物膜有能力以类似饱和的方式维持电流。本研究提出了PCC7942与铁相关的产电能力，并为该菌株的研究奠定了基础，以提高蓝藻的光生物发电和暗生物发电，包括更可持续的无介质系统。
