Pseudochelin A belongs to a larger family of catechol containing natural product siderophores, including the myxochelins (7), agrobactins (8), and fluviabactins ( ) (Fig. ). Each is biosynthesized by a hybrid non-ribosomal peptide synthetase (NRPS) and shikimate pathway, and all contain two or more 2,3dihydroxybenzoates (2,3-DHB) (10). When this family of metabolites is analyzed via tandem MS, they yield a diagnostic neutral loss of 136 m/z (6, 386 → 250 m/z; 8, 405 → 269; 9, 637 → 501 m/z; 10, 655 → 519 m/z), which is representative of the cleavage of the amide bond, liberating 2,3-DHB (10). Using this key fragmentation pattern, we analyzed the LCMS data for all fractions that inhibited S. aureus biofilm formation for the presence of these metabolites. Overall, twentyfour fractions contained 6 (63% of the active fractions), representing seventeen bacterial strains. A wider metabolomic analysis by using the Global Natural Product Social (GNPS) molecular network to analyze tandem MS data representing all fractions in the entire microbial fraction library [fractions were pooled based on polarity (A-D and E-H)] revealed sixteen strains produced a catechol containing natural product (Fig. ). Ten strains inhibited biofilm formation in S. aureus and five exhibited antimicrobial activity; one strain did not possess either activity (Table ). Eleven parent masses contained a neutral loss of 136 m/z (Fig. -S20), including 6, and clustered together when analyzed with a cosine score of 0.65 (Fig. ). Dereplication of the other parent masses clustering with 6 by using NPAtlas and AntiBase did not lead to any matches. Based on a large number of bacterial strains producing catechol containing siderophores within our relatively small microbial fraction library, it is likely that these molecules are also produced on or within the egg masses. A bulk collection of moon snail egg collars was extracted and fractionated using a similar purification scheme as the microbial crude extracts. Although these fractions exhibited some biofilm inhibition against S. aureus (Fig. ), MS-based metabolomics failed to reveal catechol siderophores. However, these metabolites could be present at concentrations below the limit of our detection.