| Biological sciences & biotechnology |
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| Isolation and screening of an electrochemically active strain Bacillus cereus sp. WL027 using phenol as fuel and preliminary study on its mechanism of electricity production |
| WANG Lili, GUO Wei, FU Chunna, YAN Hong* |
| (Key Laboratory of Green Chemical Technology of College of Heilongjiang Province, College of Chemical and Environmental Engineering, Harbin University of Science and Technology, Harbin 150040, China) |
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Abstract Microbial fuel cell (MFC) is an economic and effective way for wastewater treatment, which enables not only degradation of phenol but also conversion of biomass energy into electricity. Selection and breeding of electricigens from anode of a microbial fuel cell is the premise and foundation of MFC research; meanwhile, the problem of low energy efficiency can also be solved. Electronic delivery mechanisms of electricigens included biofilm mechanism and electron shuttle mechanism. Biofilm mechanism refers to the electricigens being attached to the electrode surface and then use cytochrome C or “nanowires” to transfer intracellular electrons to the electrode through the biofilm. Electronic shuttle mechanism concerns the use of a redox mediator to transfer electrons between the cell and the electrode. Currently, most Gram-negative bacteria with cell walls rich in cytochrome C, have been found to use cytochrome C to transfer electrons, such as Geobacter sulfurreducens, Aeromonas hydrophila and Rhodoferax ferrireducens, etc. In the process of electron transfer, the use of redox mediator for the electron transfer between the cell and the electrode is called electron shuttle mechanism. According to the source of redox mediator, it can be divided into exogenous redox mediator and endogenous redox mediator (cell autocrine). So far, little was known about the potential of Bacillus cereus to produce electricity.
In this work, an efficient phenoldegrading electricigenic bacterium was separated and screened, and its MFC was built using the obtained strain, and the efficiencies of phenol degradation and electricity production were further investigated. Meanwhile, the anode carbon felt was analyzed by scanning electron microscopy, and the cyclic voltammetry curve of the obtained strain was measured during the four growth stages (7, 18, 31 and 52 h), to explore the potential related mechanism of electricity production.
Twentyone pure strains with potential ability of electricity production were isolated, of which WL013, WL024 and WL027 strains could produce electricity, and the WL027 was the favorite electricityproducing strain. Hence, the strain WL027 was selected as the dominant strain. Based on the combination results of 16S rDNA and physiological and biochemical characteristics, the strain WL027 was identified as Bacillus cereus. This strain WL027 was electrochemically active, and its electricity was mainly generated at the stable phase during the growth of the strain. When the strain WL027 was inoculated into the MFC, the maximum voltage increased by 179 mV compared with the start voltage, with Coulombic efficiency of 64.25% and phenol degradation rate of 68.62%. The intracellular and extracellular concentrations of riboflavin were 6.10×10-3 and 1.32×10-2 mg/L respectively during the process of electricity production. The voltage was increased by 18 mV when the riboflavin was added to the MFC at the stable phase. Therefore, it can be speculated that the strain WL027 could promote the electron transport through the secretion of riboflavin in microorganisms.
In conclusion, the MFC constructed by Bacillus cereus not only can degrade phenol efficiently, but also has obvious advantages in energy conversion efficiency. Besides, the strain WL027 can promote the electron transport through the secretion of riboflavin in microorganisms.
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Published: 19 November 2016
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Corresponding Authors:
YAN Hong (http://orcid.org/0000-0002-9550-8311), Tel:+86-451-86392720，E-mail:yanhong204821@aliyun.com
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可降解苯酚的产电芽孢杆菌WL027的分离筛选及其产电机制初探
以含苯酚的生活污水为底物构建微生物燃料电池（microbial fuel cell，MFC），从处于稳定期的MFC阳极中分离筛选获得一株可降解苯酚的产电菌WL027。对菌株WL027的生理生化鉴定表明，该菌为蜡样芽孢杆菌。同时，对菌株WL027的产电性和苯酚降解情况进行了初步探讨。结果表明：菌株WL027具有电化学活性，产电期主要集中在菌株生长的稳定期；将菌株WL027接种到MFC中，MFC的最大电压较起始电压增加了179 mV，库仑效率为64.25%，苯酚降解率为68.62%；菌株WL027在产电过程中胞内和胞外核黄素质量浓度分别为6.10×10-3和1.32×10-2 mg/L；在已处于稳定期的MFC中加入核黄素，电压升高了18 mV。猜测菌株WL027可能通过分泌核黄素来促进电子在微生物中传递。
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