a, Maximum-likelihood phylogenetic tree inferred from 50 replicates showing the relationship between selected SznF homologues containing both the central domain and cupin domain (NCBI Non-Redundant Protein Sequences database, 2018) (E <1 × 10−50). The branch corresponding to S. achromogenes SznF is highlighted by a single asterisk. Bootstrap confidence values of >50 are indicated by black circles on the nodes. The amino acid sequence of UndA is used as an outgroup (highlighted as ∗∗). The sequences used to generate this tree are tabulated in Supplementary Table 2. b, Distribution of 352 SznF homologues that contain both a central domain and a cupin domain in different bacterial genera (IMG/JGI ‘all isolates’ database, 2018) (E <1 × 10−5). See also Supplementary Table 3. c, Selected biosynthetic gene clusters that encode homologues of SznF.