Involved in the non-oxidative decarboxylation and detoxification of phenolic derivatives under both aerobic and anaerobic conditions (PubMed:15979273, PubMed:18388975). Phenolic acid decarboxylase that catalyzes the reversible decarboxylation of 4-hydroxybenzoate and vanillate (PubMed:15979273, PubMed:18388975). Could also catalyze the decarboxylation of salicylate (Probable). Is not active on di- and tri-hydroxybenzoate derivatives (PubMed:18388975). 4-hydroxybenzoate + H(+) = CO2 + phenol H(+) + vanillate = CO2 + guaiacol Binds 1 prenylated FMN (prenyl-FMN) per subunit. Up-regulated by salicylate via the transcriptional regulator BsdA. A triple bsdB-bsdC-bsdD deletion mutant no longer converts vanillin to guaiacol, the conversion stops at vanillic acid (PubMed:26658822). It is not known, if phenolic acid decarboxylase forms a complex composed of BsdB, BsdC and BsdD. The term subunit is often used in reference to the operon, however there is no experimental evidence to prove the existence of the complex. Belongs to the UbiD family. YclC subfamily.