Genistein, a bioactive isoflavone, produced by the halotolerant Streptomyces albidoflavus INA 01478

The rise of antimicrobial resistance has fuelled interest in novel natural compounds. Flavonoids and isoflavonoids, known for broad pharmacological activity and low toxicity, are promising drug candidates. Although these compounds have traditionally been regarded as plant-specific metabolites, recent studies have highlighted the capacity of microorganisms to synthesise or biotransform them. Therefore, studying isoflavonoid-producing strains and their biosynthetic pathways is highly relevant for drug development.

The strain Streptomyces albidoflavus INA 01478 (GenBank accession: JBUBNM010000001) was cultivated on A4 medium (g/L): soybean meal 10.0, glucose 10.0, NaCl 5.0, CaCO₃ 2.5. Antimicrobial activity was assessed against Candida albicans ATCC 14053, Aspergillus niger ATCC 16404, A. fumigatus KPB F-37, Fusarium solani VKPM F-890 and F. oxysporum VKPM F-148. Bioactive metabolites were extracted with ethyl acetate and isolated by HPLC; preparative isolation was performed on a PuriFlash 4250 chromatograph, and NMR spectra were recorded on a Bruker AVANCE spectrometer.

The crude extracts exhibited inhibitory activity against fungi. Inhibition zones were detected of a 20–32 mm. Analytical reversed‑phase HPLC of the ethyl acetate extract revealed several peaks eluting between 3 and 15 minutes. Seven fractions were identified; fractions 3, 4, 5, and 6 demonstrated high activity against fungi. Based on NMR and mass spectrometry data, one active compound was previously identified as daidzein. In the present study, the second compound was identified as genistein.

This study demonstrates, for the first time, the biosynthesis of the isoflavonoid genistein by Streptomyces albidoflavus, establishing this strain as a promising candidate for the production of isoflavonoids.