Lichen-associated bacteria transform antibacterial usnic acid to products of lower antibiotic activity

Alba Noël (1) , Alexandre Garnier (1) , Mélanie Clément (1) , Isabelle Rouaud (1) , Aurélie Sauvager (1) , Latifa Bousarghin (2, 3) , P Vasquez-Ocmin (4) , Alexandre Maciuk (4) , Sophie Tomasi (1)

1 ISCR - Institut des Sciences Chimiques de Rennes
2 NuMeCan - Nutrition, Métabolismes et Cancer
3 MRic - Centre de Microscopie de Rennes
4 BioCIS - Biomolécules : Conception, Isolement, Synthèse

Lichens are specific symbiotic organisms harboring various microorganisms in addition to the two classic partners (algae or cyanobacterium and fungus). Although lichens produce many antibiotic compounds such as (+)-usnic acid, their associated microorganisms possess the ability to colonize an environment where antibiosis exists. Here, we have studied the behavior of several lichen-associated bacterial strains in the presence of (+)-usnic acid, a known antibiotic lichen compound. The effect of this compound was firstly evaluated on the growth and metabolism of three bacteria, thus showing its ability to inhibit Gram-positive bacteria. This inhibition was not thwarted with the usnic acid producer strain Streptomyces cyaneofuscatus. The biotransformation of this lichen metabolite was also studied. An ethanolamine derivative of (+)-usnic acid with low antibiotic activity was highlighted with chemical profiling, using HPLC-UV combined with low resolution mass spectrometry. These findings highlight the way in which some strains develop resistance mechanisms. A methylated derivative of (+)-usnic acid was annotated using the molecular networking method, thus showing the interest of this computer-based approach in biotransformation studies.

Mots clés: Actinobacteria; Alphaproteobacteria; Bacillus weihenstephenensis; Biotransformation; Firmicutes; Mabikibacter ruber; Molecular networking; Nocardia sp.; Streptomyces cyaneofuscatus; Usnic acid derivatives

Domaines: Chimie

Alba Noël, Alexandre Garnier, Mélanie Clément, Isabelle Rouaud, Aurélie Sauvager, et al.. Lichen-associated bacteria transform antibacterial usnic acid to products of lower antibiotic activity. Phytochemistry, 2021, 181, pp.112535. ⟨10.1016/j.phytochem.2020.112535⟩. ⟨hal-02998957⟩