Ferric iron and extracellular electron shuttling increase xylose utilization and butanol production during fermentation with multiple solventogenic bacteria

• Published in: Applied microbiology and biotechnology 2017-11, Vol.101 (21), p.8053-8061
• Main Authors: Popovic, Jovan, Ye, Xiaofeng, Haluska, Anne, Finneran, Kevin T.
• Format: Article
• Language: English
• Subjects: Anthraquinone; Anthraquinones - metabolism; Bacteria; Bioenergy and Biofuels; Biofuels; Biomedical and Life Sciences; Biosynthesis; Biotechnology; Butanol; Butanols - metabolism; Clostridium; Clostridium beijerinckii - metabolism; Cluster Analysis; Crystal structure; Culture Media - chemistry; Cytosol - chemistry; DNA, Bacterial - chemistry; DNA, Bacterial - genetics; DNA, Ribosomal - chemistry; DNA, Ribosomal - genetics; Electron Transport; Electrons; Fermentation; Ferric Compounds - metabolism; Hydrogen production; Iron; Life Sciences; Lignocellulose; Microbial Genetics and Genomics; Microbiology; Phylogeny; Rhizobiaceae - classification; Rhizobiaceae - genetics; Rhizobiaceae - metabolism; Riboflavin; Riboflavin - metabolism; RNA, Ribosomal, 16S - genetics; rRNA 16S; Sequence Analysis, DNA; Solvents; Sugar; Sugars - analysis; Utilization; Vitamin B; Xylose; Xylose - metabolism
• ISSN: 0175-7598; 1432-0614
• DOI: 10.1007/s00253-017-8533-9

Xylose is the second most abundant sugar derived from lignocellulose; it is considered less desirable than glucose for fermentation, and strategies that specifically increase xylose utilization in wild-type cells are goals for biofuel production. Xylose consumption, butanol production, and hydrogen production increased in both Clostridium beijerinckii and a novel solventogenic bacterium (strain DC-1) when anthraquinone-2,6,-disulfonate (AQDS) or riboflavin were used as redox mediators to transfer electrons to poorly crystalline Fe(OH) 3 as an extracellular electron sink. Strain DC-1 was most closely related to Rhizobiales bacterium Mfc52 based on 95% 16S rRNA gene sequence similarity, which demonstrates that this response is not limited to a single genus of xylose-fermenting bacteria. Xylose utilization and butanol production were negligible in control incubations containing cells plus 3% ( w / v ) xylose alone during a 10-day batch fermentation, for both strains tested (n-butanol titers of 0.05 g L −1 ). Micromolar concentrations of AQDS and riboflavin were added as electron shuttling compounds with poorly crystalline Fe(OH) 3 as an insoluble electron acceptor, and respective n-butanol titers increased to 6.35 and 7.46 g L −1 . Increases in xylose consumption for the iron treatments were relatively high, from less than 0.49 g L −1 (xylose alone, no iron or electron shuttling molecules) to 25.98 and 29.15 g L −1 for the AQDS and riboflavin treatments, respectively. Hydrogen production was also 3.68 times greater for the AQDS treatment and 5.27 greater for the riboflavin treatment relative to controls. Strain DC-1 data were similar, again indicating that the effects are not specific to the genus Clostridium .