acetobutylicum[81], also found in a number of Thermoanaerobacter species, these oxidoreductases may also be capable of converting pyruvate into acetyl-CoA. Formate production was consistent with the presence of PFL (Cthe_0505). While a number of studies have reported formate production [3–5, 35, 55], others have not [50, 68, 82]. These discrepancies may be a result of the use of different selleck chemical www.selleckchem.com/products/NVP-AUY922.html detection methods (gas chromatography

vs high pressure liquid chromatography), fermentation conditions (batch with no pH control vs bioreactor with pH control), or media composition (complex vs minimal). Expression levels of PFL were lower than that of POR Cthe_2390-2393, in agreement with end-product accumulation rates and previously reported enzyme activities [4]. Of the four putative PFL-activating enzymes (Cthe_0506, Cthe_0647, Cthe_1167, Cthe_1578) required for glycyl radical formation on the C-terminal portion of PFL [83, 84], only Cthe_0506 was detected. While this agreed with high mRNA levels in cellobiose [22] and

cellulose grown batch cultures [37], Raman et al. also reported high expression levels of Cthe_0647 during fermentation. While PFL and PFL-activating enzyme Cthe_0506 are encoded next to each other, the 3-fold difference in expression levels suggests that they are either transcribed independently as in Streptococcus bovis[85], or have different protein Acadesine stabilities. While LDH was expressed,

albeit at lower levels than detected PORs and PFL, lactate production was not detected under the conditions tested. In C. thermocellum Galeterone LDH has been shown to be allosterically activated by fructose-1,6-bisphosphate (FDP), [20] while in Caldicellulosiruptor saccharolyticus, a close relative to C. thermocellum, LDH is activated by FDP and ATP, and inhibited by NAD+ and PPi[21]. While lactate production in C. thermocellum was observed in batch cultures under carbon excess [3] and low culture pH (Rydzak et al. unpublished), this may be due to high intracellular FDP, concentrations, high NADH/NAD+ ratios, and/or high ATP/PPi ratios during transition to stationary phase [21], which may have not been reached under our growth conditions. Acetyl-CoA/ethanol/acetate branchpoint Catabolism of acetyl-CoA into ethanol and acetate plays an important role in NADH reoxidation and energy conservation, respectively. Acetyl-CoA can be converted into ethanol directly using a bi-functional acetaldehyde/alcohol dehydrogenase (Cthe_0423; adhE), or indirectly via an NADH-dependant aldehyde dehydrogenase (Cthe_2238; aldH) and a number of iron containing alcohol dehydrogenases (Cthe_0101, Cthe_0394, Cthe_2579; adh). Expression of Cthe_2238 (aldH), Cthe_0394 (adhY), and Cthe_2579 (adhZ) has been confirmed by real-time PCR [35]. Of these ADHs, AdhE was the most abundant ADH detected (Figure  3b).