Identification and characterization of two new types of bacterial L-serine dehydratases and assessment of the function of the ACT domain.

•Two new types of bacterial iron–sulfur l-serine dehydratases have been identified.•A total of four types have now been identified that differ in domain arrangement.•The types differ in oxygen sensitivity and monovalent cation requirement.•The Type 4 remains inactive after reconstitution and may be a pseudoenzyme.