Biofilm production by Zymomonas mobilis enhances ethanol production and tolerance to toxic inhibitors from rice bran hydrolysate
Biofilm production by Zymomonas mobilis enhances ethanol production and tolerance to toxic inhibitors from rice bran hydrolysate
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2014
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eng
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application/pdf
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9 pages
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New Biotechnology Volume 31, Number 5 September 2014, 451-459
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Abstract
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.