Short communication Direct energy conversion from xylose using xylose dehydrogenase surface displayed bacteria based enzymatic biofuel cell Lin Xia a , Bo Liang a , Liang Li a , Xiangjiang Tang a , Ilaria Palchetti b , Marco Mascini b , Aihua Liu a,n a Laboratory for Biosensing, Qingdao Institute of Bioenergy and Bioprocess Technology, and Key Laboratory of Bioenergy, Chinese Academy of Sciences, 189 Songling Road, Qingdao 266101, China b Dipartimento di Chimica, Universita degli Studi di Firenze, Via della Lastruccia, 3 50019 Sesto Fiorentino, Italy article info Article history: Received 7 November 2012 Received in revised form 8 January 2013 Accepted 9 January 2013 Available online 29 January 2013 Keywords: Biofuel cell Direct energy conversion Xylose dehydrogenase displayed bacteria Efficient utilization of lignocellulose biomass abstract Xylose is an important and major monosaccharide that extensively exists in the cellulose fermentation industry. Here we present the first report on the direct energy conversion from xylose achieved by using novel xylose dehydrogenase (XDH) surface displayed bacteria (XDH-bacteria) based enzymatic biofuel cell. The maximum power density and the open-circuit potential of the cell are 63 mWcm 2 and 0.58 V, respectively. The as-prepared BFC holds great potential to make use of biomass from lignocellu- lose degradation as source energy, which avoids the bottleneck in conversion of xylose to ethanol met by conventional fermentation method. & 2013 Elsevier B.V. All rights reserved. 1. Introduction The drive for research on alternative sources of green energy is boosted by the inevitable depletion of the fossil fuels and the increasing awareness of environmental problems (Agarwal, 2007; Dhepe and Fukuoka, 2008; Jefferson, 2006). Biofuel cells (BFCs), a special kind of fuel cells where enzymes or microorganisms are employed as the biocatalysts and biomass as the fuels for the conversion of chemical energy to electricity, are worthwhile candidates to address these issues (Bullen et al., 2006; Cracknell et al., 2008; Du et al., 2007). Intensive researches have been done on glucose-based BFC (Gao et al., 2010; Li et al., 2009; Wen et al., 2011; Zebda et al., 2011) because of its possible promise for implantable power device which utilizes blood sugar as fuel source. Xylose is also an important monosaccharide that extensively exists in the cellulose fermentation industry, comprising about 17–31% of lignocellulose materials. Conventionally, the conversion of xylose to fuel ethanol was achieved either by a thermochemical method or microorganisms’ fermentation approach (Dien et al., 2003; Lin and Tanaka, 2006). Usually, the thermochemical process requires a harsh condition which is energy-consuming. On the other hand, as for microorganisms’ fermentation method, the process was very slow with a poor yield (Lin and Tanaka, 2006), which is most probably due to the low resistance of microorganisms to higher concentrations of ethyl alcohol. Another disadvantage of these processes is the production of various by-products, primarily acetic and lactic acids, which will lower the utilization efficiency. In contrast, enzymatic bioelectrocatalytic oxidation of xylose would open a new avenue for using xylose as a direct energy source. To date, there are a few reports on electricity generation from xylose-based microbial fuel cells (Huang and Logan, 2008; Huang et al., 2008). However, for microbial fuels, the longer electron transfer pathway and the mass transport problems around the electrodes impaired the energy conversion efficiency. Further, the practical application of xylose based enzymatic biofuel cells could be greatly limited by the cost of enzyme purification. Moreover, the road for the xylose based enzymatic biofuel cell is blocked by the poor stability of the purified xylose dehydrogenase (XDH) at ambient conditions of temperature and pH as well as the undesirable long-term durability (Lapinsonniere et al., 2012; Li et al., 2012). Consequently, an enzymatic biofuel cell that could achieve direct and efficient electricity production from xylose is much desirable. The strategy of bacteria surface expression of redox enzymes is an ideal method to handle these issues. Recently, this strategy has been demonstrated in the application of xylose sensors (Li et al., 2013, 2012; Liang et al., 2012) and glucose microbial biofuel cells Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/bios Biosensors and Bioelectronics 0956-5663/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.bios.2013.01.026 n Corresponding author. Tel.: þ86 532 8066 2758. E-mail address: liuah@qibebt.ac.cn (A. Liu). Biosensors and Bioelectronics 44 (2013) 160–163