# Lactuchelins represent lipopeptide siderophores produced by Pseudomonas lactucae that inhibit Xanthomonas campestris

## TL;DR

A bacterium called Pseudomonas lactucae produces compounds called lactuchelins that inhibit a plant pathogen, offering a potential biocontrol strategy for seeds.

## Contribution

Discovery of lactuchelins, a new class of lipopeptide siderophores, and their role in microbial competition on seeds.

## Key findings

- Pseudomonas lactucae CFBP 13502 inhibits Xanthomonas campestris via exometabolites.
- Lactuchelins are lipopeptide siderophores that chelate iron, reducing pathogen growth.
- Transcriptomic and metabolomic analyses confirm the role of a gene cluster in lactuchelin production.

## Abstract

The seed is a habitat with limited resources and space. Although it is widely accepted that microbial competition is a key driver of the assembly of seed-associated microbial communities, the underlying mechanisms of this competition are not well understood. The initial objective of this work was to assess the importance of contact-independent microbial competition between the phytopathogenic bacterium Xanthomonas campestris pv. campestris 8004 (Xcc8004) and 30 strains representative of the bacterial populations most commonly associated with radish (Raphanus sativus) seeds. We identified Pseudomonas lactucae CFBP 13502 as a potent inhibitor of Xcc8004, mediated by exometabolites, specifically induced by certain seed-borne strains. Transcriptomic analysis linked this inducible activity to the upregulation of a gene cluster encoding a lipopeptide siderophore. Targeted gene deletion in P. lactucae CFBP 13502 confirmed that this cluster is essential for antagonism against Xcc8004. Furthermore, iron supplementation abolished this inhibitory effect, strongly supporting iron chelation as the underlying mechanism. Through comparative metabolomics, we elucidated the structure of a family of lipopeptide siderophores, produced by P. lactucae CFBP 13502, which we named lactuchelins. Our findings provide molecular evidence of competitive exclusion mechanisms at the seed microbiome interface, highlighting lactuchelins as a promising avenue for the development of seed-based biocontrol strategies against seed-borne phytopathogens.

Graphical Abstract