Comprehensive calculation of product and ATP yields for glucose fermentation

In a detailed analysis of glucose fermentation by microbial communities, researchers have quantified the energy yield and the various biochemical pathways involved in the process. The study examined the breakdown of glucose into 11 fermentation products, such as alcohols, acids, and ketones. This analysis incorporated 75 reactions that allowed for energy conservation through both substrate-level phosphorylation and transport-coupled phosphorylation. The electron carriers involved in this process were ferredoxin, NADH, and quinol.

Upon conducting a comprehensive calculation, the researchers determined 195,629 unique conversions of glucose into fermentation products. Out of these conversions, approximately 50% had a non-zero ATP yield. The conversion processes with the same product stoichiometry could yield different ATP amounts. For instance, the conversion of glucose to propionate and acetate could be accomplished via different subnetworks, leading to a range of 23 distinct ATP/glucose yields.

Interestingly, even the conversion of glucose to lactate exhibited 12 different yields, spanning from 0 to 4.5 ATP per glucose molecule. The driving force behind these conversions was found to decrease as the ATP yield increased. However, the number of reactions used did not correlate with the ATP yield. The known catabolic conversions that occur during anaerobic digestion may merely represent the tip of the iceberg, as there could be numerous other undiscovered pathways contributing to this metabolic process.