PubMed · 2747265
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G S Hirschmann, E Ferro. 1989. Indigo from Eupatorium laeve.. https://doi.org/10.1016/0378-8741(89)90115-3
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There is an increasing commercial demand for naturally sourced indigo that meets the purity standards set by the synthetic product. This study concerns the indigo made from leaves of woad (Isatis tinctoria L.), and in particular its interaction with particulate impurities arising from soil and plant materials. Also, a more reliable method using N-methyl-2-pyrrolidone has been developed for the spectrophotometric determination of indigo. In a novel application of fluorescence spectroscopy, indoxyl intermediates in indigo formation are shown to be stable for minutes. The main indigo precursor from woad can be adsorbed onto Amberlite XAD16 in conformity with a Langmuir isotherm, but indigo precursors break down on this and other resin beads to yield indigo and red compounds. Indigo made from indoxyl acetate aggregates into particles, the size distribution of which can be modified by the inclusion of a fine dispersion of calcium hydroxide. Bright field microscopy of indigo products made under defined conditions and scanning electron microscopy combined with energy-dispersive X-ray analysis reveal the relationship of indigo with particulate materials. A model illustrating the interaction of indigo with particulate contaminants is developed on the basis of the results obtained, and recommendations are made for improving the purity of natural indigo.
The transformation of indole to indigo by microorganisms expressing styrene monooxygenase (SMO) has been studied. Styrene and indole are structurally very similar, and thus we looked at a variety of styrene-degrading strains for indole transformation to indigo. Two strains, Pseudomonas putida S12 and CA-3, gave a blue color on solid media when grown in the presence of indole. Indole induces its own transformation on solid media but is a poor inducer in liquid media. Styrene is the best inducer of indole transformation in both strains. Arginine represses styrene consumption and indigo formation rates in P. putida S12 compared to phenylacetic acid-grown cells, while the opposite effect is seen for P. putida CA-3. Characterization of an SMO- and styrene oxide isomerase (SOI)-negative transposon mutant of P. putida CA-3 and an SOI-negative N-methyl-N'-nitro-N-nitrosoguanidine mutant of P. putida S12 reveals the involvement of both SMO and SOI in indole transformation to indigo. Both strains stoichiometrically produce high-purity indigo from indole.
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