New variochelins from soil-isolated Variovorax sp. H002.

The soil bacterial genus Variovorax produce distinct photoreactive siderophores that may play a crucial role in the iron cycle within the rhizosphere. This study focused on exploring the natural products of the soil-isolated Variovorax sp. H002, leading to the isolation of variochelins A-E ( 1 - 5 ), a series of lipohexapeptide siderophores. NMR and MS/MS analyses revealed that these siderophores share a common core structure - a linear hexapeptide with β-hydroxyaspartate and hydroxamate functional groups, serving in iron-binding coordination. Three new variochelins C-E ( 3 - 5 ) were characterized by varied fatty acyl groups at their N -termini; notably, 4 and 5 represent the first variochelins with N -terminal unsaturated fatty acyl groups. Furthermore, the variochelin biosynthetic gene cluster was identified through draft genome sequencing and gene knockout experiments. Compounds 1 - 5 exhibited antimicrobial activities against Gram-negative bacteria, including several soil-isolated plant pathogens.