Electron shuttling to ferrihydrite selects for fermentative rather than Fe3+—reducing biomass in xylose—fed batch reactors derived from three different inoculum sources

• Published in: Biotechnology and bioengineering 2018-03, Vol.115 (3), p.577-585
• Main Authors: Popovic, Jovan, Finneran, Kevin T.
• Format: Article
• Language: English
• Subjects: Acid production; Anthraquinone; Batch reactors; Biomass; Bioreactors; bioremediation; butanol; Disease control; Electrons; Fed batch; Fermentation; hydrogen; Hydrogen production; Inoculum; Iron; Microorganisms; mixed culture; Riboflavin; rRNA 16S; Substrates; Wetwood; Xylose
• ISSN: 0006-3592; 1097-0290
• DOI: 10.1002/bit.26494

Reports suggest that ferric iron and electron shuttling molecules will select for Fe3+—reducer dominated microbial biomass. We investigated the influence of the redox mediators anthraquinone‐2,6‐disulfonate (AQDS) and riboflavin using xylose as the sole fermentation substrate, with or without ferric iron. Electron shuttling to insoluble ferrihydrite enhanced solventogenesis, acidogenesis, hydrogen production, and xylose consumption, relative to the cells plus xylose controls in fermentations inoculated with woodland marsh sediment, wetwood disease, or raw septic liquid, over multiple transfers in 15‐day batch fermentations. 16S rRNA gene based community analyses indicated that ferrihydrite alone, and AQDS/riboflavin plus ferrihydrite, immediately shifted native heterogeneous communities to those predominantly belonging to the Clostdridiales, rather than stimulating Fe3+ respiring populations. Data were similar irrespective of the inoculum source, suggesting that Fe3+ and/or electron shuttling compounds select for rapid proliferation of fermentative genera when fermentable substrates are present, and increases the extent of xylose consumption and solvent production. Data demonstrated that ferric iron, electron shuttling molecules (aka redox mediators), and xylose preferentially selected for butanol‐generating fermenters rather than ferric‐iron reducers from three different environmental sources. Results also indicated that xylose fermentation and butanol production can be influenced in mixed microbial consortia derived from environmental media, suggesting that biofuels can be produced using mixed cultures.