Comparison of the LC-HRESIMS profiles of E. coli pET28-ptetO::micABCDEFG-gfpv2 transformants with those of empty vector transformants, both grown in minimal M9 medium supplemented with a vitamin mix (see materials and methods and Table ), revealed MS features that were only present in cells containing the mic BGC (Fig. ). Full MS spectra for these peaks showed [M+H] + ions for non-halogenated compounds of m/z 658.417 (13) and 672.433 (14) as well as minor amounts of 495.354 (15) (Fig. ). A monochlorinated version of 13 (m/z 692.378, [M+H] + ) could also be detected (16). LC-HRESI-MS/MS analysis of the most abundant compounds 13, 14 and 16 (Fig. ) indicated that these new metabolites are microginins related to 1-12 in which Leu or Ile replaced Htyr/Hphe. The formation of 13-16 can be explained by the fact that the mic BGC does not include the hphABCD operon necessary for the production of Htyr/Hphe. In fact, this set of genes is found elsewhere in the genome of LEGE 91341, as part of an anabaenopeptin BGC (Table ). Supplementation of the mic BGC transformant cultures with exogenous Hphe led to the detectable production of 5 and 6 (Fig. ) -as confirmed by MS/MS analysis (Fig. ) -but did not lead to the production of dichlorinated 4 (Fig. ). Dichlorinated microginin variants were also not observed in the absence of exogenously supplied Hphe, suggesting that the MicC halogenase is considerably less effective in E. coli.