U.S. flag

An official website of the United States government

Dot gov

Official websites use .gov
A .gov website belongs to an official government organization in the United States.


Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.


Main content area

Redox mediators modify end product distribution in biomass fermentations by mixed ruminal microbes in vitro

Michael A. Nerdahl, Paul J. Weimer
AMB Express 2015 v.5 no.1 pp. 1-8
Panicum virgatum, beta oxidation, biomass, carbon, dyes, energy, fermentation, gas production (biological), in vitro studies, methane, methane production, paraquat, redox reactions, rumen bacteria, rumen fermentation, tannins, volatile fatty acids
The fermentation system of mixed ruminal bacteria is capable of generating large amounts of short-chain volatile fatty acids (VFA) via the carboxylate platform in vitro. These VFAs are subject to elongation to larger, more energy-dense products through reverse β-oxidation. This study examined the effect of several redox mediators (neutral red, methyl viologen, safranin T, tannic acid) as alternative electron carriers for the mixed ruminal bacteria during the fermentation of biomass (ground switchgrass not subjected to other pretreatments) and their potential to enhance elongation of end products to medium-chain VFAs with no additional run-time. Neutral red (1 mM), in particular, facilitated chain elongation, increasing average VFA chain length from 2.42 to 2.97 carbon atoms per molecule while simultaneously inhibiting methane accumulation by over half and keeping total end-product C quantity consistent. The ability of redox dyes to act as alternative electron carriers suggested that ruminal fermentation is inherently manipulable toward reducing methanogenesis and retaining a higher fraction of substrate energy in the form of VFA.