Abstract
Extracellular electron transfer involving microbes is important as it closely reflects the ability of cells to communicate with the environment. However, there are few reports on electron transfer mechanisms of pure microalgae and a lack of any model alga to study the transfer processes. In the present study, nine green microalgae species were isolated from wastewater and characterized in terms of their ability to transfer electrons between cells and an electrode. One species showed direct electron transfer via membrane-associated proteins and indirect electron transfer via secreted oxygen. The microalga was identified as Desmodesmus sp. based on phylogenetic analysis and electron microscopy. Electrochemical tests demonstrated that Desmodesmus sp. was able to act as a cathodic microorganism. Stable current densities of −0.24, 35.54 and 170 mA m−2 were achieved at potentials of +0.2, −0.2 and −0.4 V, respectively, under illumination. Dissolved oxygen concentration measurement showed gradients within the microalgae biofilm: 18.3 mg L−1 in light decreasing to 4.29 mg L−1 in the dark. This study diversified the exoelectrogen library and provided a potential model microalga to explore the associated mechanism of extracellular electron transfer.
Highlights
Bioelectrochemical systems (BES) are paid increasing attentions because of their ability to provide power and to treat wastewater with the assistance of electroactive microorganisms [1]
Direct electron transfer is via electroactive proteins, while indirect transfer is with the aid of redox mediators secreted by bacteria
The results showed that strain A8 should be assigned to the genus Desmodesmus and was most closely related to Desmodesmus hystrix isolate NDem 9/21 T-9W DQ417551 (98% sequence similarity), Desmodesmus brasiliensis FR865708 (96% sequence similarity), and Desmodesmus pannonicus FR865710 (94% sequence similarity)
Summary
Bioelectrochemical systems (BES) are paid increasing attentions because of their ability to provide power and to treat wastewater with the assistance of electroactive microorganisms [1]. Adoption of microalgae in BES can produce organic matter and simultaneously consume carbon dioxide on an electrode surface [5,6]. Other functions, such as N, P absorption [7], biodiesel production [8] and biomass supply [9] increase the potential application of microalgae in renewable energy generation and wastewater treatment. In view of increasing interest in adopting photosynthetic microalgae, a more comprehensive insight into the electron transfer mechanism between microalgae and electrode is of interest. Desmodesmus sp. isolated from wastewater was investigated in terms of electron transfer mechanism and application to enhance the current generation under various conditions
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