Fig. 7.

The degradation of protocatechuic acid is categorized as 3, 4-cleavage pathway, 4, 5-cleavage pathway, and 2, 3-cleavage pathway. However, the degradation of catechol is mainly catalyzed by dioxygenases through ortho- or meta-cleavage pathway [120]. After completing aromatic ring cleavage, the molecules succinate, acetyl-CoA, and pyruvate enter the TCA cycle for cell growth and products’ synthesis