Abstract
Background: Major challenges associated with the fermentation of lignocellulosic hydrolysates are the reduction in the operating cost and minimizing the complexity of the process. Zymomonas mobilis biofilm has been emerged to resolve these complexities. Biofilm has been reported to tolerate to the toxic inhibitors and easily manipulated toward the cell recycle through the cell immobilization. Results: Z. mobilis ZM4 and TISTR 551 were able to develop biofilms on DEAE cellulose under the differences in the morphologies. Z. mobilis ZM4 developed homogeneous biofilm that brought DEAE fiber to be crosslinking, while Z .mobilis TISTR 551 developed heterogeneous biofilm in which crosslinking was not observed. Ethanol production under batch and repeated batch fermentation of rice bran hydrolysate containing toxic inhibitors were compared between these two biofilms. TISTR 551 biofilm produced the maximum yield (Y P/S ) of 0.43 ± 0.09 g ethanol/ g glucose (83.89% theoretical yield). However the repeated batch could not be proceeded due to the bacterial detachment. Z. mobilis ZM4 biofilm produced the maximum yield (Y P/S ) of 0.177 ± 0.05 g ethanol/ g glucose (34.74% theoretical yield) in the batch culture and the biofilm remained intact to proceed along the repeated batch. The highest ethanol yield (Y P/S ) in the repeated batch of Z. mobilis ZM4 was 0.354 ± 0.07 g ethanol/ g glucose (69.51% theoretical yield). Conclusions: Homogeneous biofilm structure of Z. mobilis provided more recycle beneficial over the heterogeneous biofilm structure for the ethanol production from lignocellulosic hydrolysate. Normal 0 21 false false false EN-US X-NONE TH st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:Tabla normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:Calibri,sans-serif; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;}
Highlights
Lignocellulosic biomass (LCB) is an abundant, renewable source of carbohydrates for microbial conversion to value added chemicals and fuels
The purpose of this study was to describe the use of Z. mobilis immobilization in the form of biofilm on DEAE-cellulose to enhance the ethanol production from the rice bran hydrolysate
Z. mobilis has been effectively used for ethanol productions in various glucose rich medium and some lignocellulosic materials [27,30]
Summary
Lignocellulosic biomass (LCB) is an abundant, renewable source of carbohydrates for microbial conversion to value added chemicals and fuels. Relatively high concentrations of inhibitory compounds are formed during the process including furfural hydroxymethylfurfural (HMF), acetic acid, formic acid, levulinic acids and vanillin [4] These toxic inhibitors are found to have negative effects over microbial growth, metabolism and ethanol production of many ethanologenic microorganisms [5,6,7]. Ethanol production under batch and repeated batch fermentation of rice bran hydrolysate containing toxic inhibitors were compared between these two biofilms. Z. mobilis ZM4 biofilm produced the maximum yield (YP/S) of 0.177 ± 0.05 g ethanol/g glucose (34.74% theoretical yield) in the batch culture and the biofilm remained intact to proceed along the repeated batch. Conclusions: Homogeneous biofilm structure of Z. mobilis provided more recycle beneficial over the heterogeneous biofilm structure for the ethanol production from lignocellulosic hydrolysate
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