Five classes of GREs include: GRE formate-lyases (pyruvate formate-lyases, PFL, and ketobutyrate formate-lyases, TdcE); GRE 1,2-eliminases (choline trimethylamine-lyase, CutC, glycerol dehydratase, GDH, and propane-1,2-diol dehydratase, PDH); GRE ribonucleotide reductases (class III RNRs); and GRE decarboxylases (4-hydroxyphenylacetate decarboxylase, HPAD); and X-succinate synthases (XSSs where X= toluene in the case of benzylsuccinate synthase, BSS).