Todhanakasem Tatsaporn, Sangsutthiseree Atit, Areerat Kamonchanok, Young Glenn M, Thanonkeo Pornthap
Faculty of Biotechnology, Assumption University, 10240, Thailand.
Faculty of Biotechnology, Assumption University, 10240, Thailand.
N Biotechnol. 2014 Sep 25;31(5):451-9. doi: 10.1016/j.nbt.2014.06.002. Epub 2014 Jun 12.
Microorganisms play a significant role in bioethanol production from lignocellulosic material. A challenging problem in bioconversion of rice bran is the presence of toxic inhibitors in lignocellulosic acid hydrolysate. Various strains of Zymomonas mobilis (ZM4, TISTR 405, 548, 550 and 551) grown under biofilm or planktonic modes were used in this study to examine their potential for bioconversion of rice bran hydrolysate and ethanol production efficiencies. Z. mobilis readily formed bacterial attachment on plastic surfaces, but not on glass surfaces. Additionally, the biofilms formed on plastic surfaces steadily increased over time, while those formed on glass were speculated to cycle through accumulation and detachment phases. Microscopic analysis revealed that Z. mobilis ZM4 rapidly developed homogeneous biofilm structures within 24 hours, while other Z. mobilis strains developed heterogeneous biofilm structures. ZM4 biofilms were thicker and seemed to be more stable than other Z. mobilis strains. The percentage of live cells in biofilms was greater than that for planktonic cells (54.32 ± 7.10% vs. 28.69 ± 3.03%), suggesting that biofilms serve as a protective niche for growth of bacteria in the presence of toxic inhibitors in the rice bran hydrolysate. The metabolic activity of ZM4 grown as a biofilm was also higher than the same strain grown planktonically, as measured by ethanol production from rice bran hydrolysate (13.40 ± 2.43 g/L vs. 0.432 ± 0.29 g/L, with percent theoretical ethanol yields of 72.47 ± 6.13% and 3.71 ± 5.24% respectively). Strain TISTR 551 was also quite metabolically active, with ethanol production by biofilm and planktonically grown cells of 8.956 ± 4.06 g/L and 0.0846 ± 0.064 g/L (percent theoretical yields were 48.37 ± 16.64% and 2.046 ± 1.58%, respectively). This study illustrates the potential for enhancing ethanol production by utilizing bacterial biofilms in the bioconversion of a readily available and normally unusable low value by-product of rice farming.
微生物在木质纤维素材料生产生物乙醇过程中发挥着重要作用。米糠生物转化过程中的一个挑战性问题是木质纤维素酸水解产物中存在有毒抑制剂。本研究使用了在生物膜或浮游模式下生长的多种运动发酵单胞菌菌株（ZM4、TISTR 405、548、550和551），以考察它们对米糠水解产物的生物转化潜力和乙醇生产效率。运动发酵单胞菌很容易在塑料表面形成细菌附着，但在玻璃表面则不会。此外，在塑料表面形成的生物膜会随着时间稳步增加，而在玻璃表面形成的生物膜据推测会经历积累和脱离阶段的循环。显微镜分析显示，运动发酵单胞菌ZM4在24小时内迅速形成均匀的生物膜结构，而其他运动发酵单胞菌菌株形成的是异质生物膜结构。ZM4生物膜比其他运动发酵单胞菌菌株的生物膜更厚，似乎也更稳定。生物膜中活细胞的百分比高于浮游细胞（54.32±7.10%对28.69±3.03%），这表明在米糠水解产物存在有毒抑制剂的情况下，生物膜为细菌生长提供了一个保护性生态位。通过米糠水解产物生产乙醇来衡量，作为生物膜生长的ZM4的代谢活性也高于浮游生长的同一菌株（分别为13.40±2.43 g/L对0.432±0.29 g/L，理论乙醇产率分别为72.47±6.13%和3.71±5.24%）。菌株TISTR 551的代谢活性也相当高，生物膜生长和浮游生长细胞的乙醇产量分别为8.956±4.06 g/L和0.0846±0.064 g/L（理论产率分别为48.37±16.64%和2.046±1.58%）。本研究说明了在水稻种植中一种现成且通常未被利用的低价值副产品的生物转化过程中，利用细菌生物膜提高乙醇产量的潜力。
