True fermentation strictly occurs under:
Fermentat+I2:I530ion represents an ancient energy-yielding strategy where organic molecules serve as both electron donors and acceptors without involvement of external terminal acceptors like oxygen or nitrate. Glycolysis converts glucose to pyruvate with net production of two ATP via substrate-level phosphorylation, mediated by phosphoglycerate kinase and pyruvate kinase, reducing NAD+ to NADH at glyceraldehyde-3-phosphate dehydrogenase step. Under strictly anaerobic conditions, cells cannot operate electron transport chain, so NADH must be reoxidized by transferring electrons to pyruvate or
Ref: Berg et al., Biochemistry 9th ed., Chapter 16 Glycolysis and Fermentation; NCBI Bookshelf NBK22356.