Insights into electron flux through manipulation of fermentation conditions and assessment of protein expression profiles in Clostridium thermocellum.

While annotation of the genome sequence of Clostridium thermocellum has allowed predictions of pathways catabolizing cellobiose to end products, ambiguities have persisted with respect to the role of various proteins involved in electron transfer reactions. A combination of growth studies modulating carbon and electron flow and multiple reaction monitoring (MRM) mass spectrometry measurements of proteins involved in central metabolism and electron transfer was used to determine the key enzymes involved in channeling electrons toward fermentation end products. Specifically, peptides belonging to subunits of ferredoxin-dependent hydrogenase and NADH:ferredoxin oxidoreductase (NFOR) were low or below MRM detection limits when compared to most central metabolic proteins measured.