Involved in 'Ser-type' sulfatase maturation under anaerobic conditions. Links the heparin and the chondroitin sulfate utilization pathways which contribute to the colonization of the intestinal tract. May catalyze the activation of chondro-6-sulfatase, i.e. the post-translational modification of a specific serine residue into 3-oxoalanine (also known as C(alpha)-formylglycine (FGly)), by a free radical chemical mechanism initiated via the reductive cleavage of S-adenosyl-L-methionine (SAM). Is also able to oxidize a cysteine residue in a synthetic substrate to FGly in vitro, but not in a recombinant Cys-type sulfatase in vivo. But since B.thetaiotaomicron possesses only Ser-type sulfatases, the oxidation of serine residues to FGly is the sole physiological activity. L-seryl-[sulfatase] + S-adenosyl-L-methionine = 3-oxo-L-alanyl-[sulfatase] + 5'-deoxyadenosine + H(+) + L-methionine Binds 3 [4Fe-4S] clusters (PubMed:20218986). The first cluster is coordinated with 3 cysteines and an exchangeable S-adenosyl-L-methionine (By similarity). Protein modification; sulfatase oxidation. Belongs to the radical SAM superfamily. Anaerobic sulfatase-maturating enzyme family.