# Bioguided-isolation of antimicrobial compounds against phytopathogens and human pathogens from lichen-associated bacteria

Flavia Bollaro, Ghada Derbaj, Isabelle Rouaud, Assia Dreux-Zhiga, Jean-Yves Berthon, Clémence Defois-Fraysse, Sylvain Tranchimand, Sophie Tomasi

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Flavia Bollaro, Ghada Derbaj, Isabelle Rouaud, Assia Dreux-Zhiga, Jean-Yves Berthon, et al. Bioguided-isolation of antimicrobial compounds against phytopathogens and human pathogens from lichen-associated bacteria. Phytochemistry Letters, 2025, International Congress on Natural Products Research 2024 (ICNPR2024), 69 (Supplém), pp.103255. 10.1016/j.phytol.2025.103255. hal-05505018

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Submitted on 11 Feb 2026

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Bioguided- isolation of antimicrobial compounds against phytopathogens and human pathogens from lichen-associated bacteria

Bollaro Flavia<sup>a,b*</sup>, Derbaj Ghada<sup>a</sup>, Rouaud Isabelle<sup>a</sup>, Dreux-Zhiga Assia<sup>b</sup>, Berthon Jean-Yves<sup>b</sup>, Defois-Fraysse Clémence<sup>b</sup>, Tranchimand Sylvain<sup>a</sup>, Tomasi Sophie<sup>a</sup>

The World Health Organization places Antimicrobial Resistance (AMR) to be one of the greatest threats to global health (Murray *et al.*, 2022). The emergence of AMR in humans, animals and plants highlights the need for a "One Health" strategy (Despotovic *et al.*, 2023). This project goal is the investigation of the antimicrobial potential of a collection of 500 strains from the microflora of several lichen samples of *Rhizocarpon geographicum* against two phytopathogens: *Erwinia amylovora* (Piqué *et al.*, 2015), *Venturia inaequalis* (González-Domínguez, Armengol and Rossi, 2017) and against three human bacterial pathogens (*Pseudomonas aeruginosa*, *Staphylococcus aureus*, *Escherichia coli*). Lichen samples were collected from coastal and terrestrial areas, allowing them to undergo various biotic and abiotic stresses. Moreover, lichens, as holobionts, constitute micro-ecosystems that shelter unidentified microbial communities which could take part in the holobiont's defense against pathogens (Miral *et al.*, 2022).

The first step of our study involved culturing 286 lichen-associated bacteria in a suitable medium, collecting the supernatant and pellet at an appropriate phase for the production of specialized metabolites and evaluating their activities against the targeted pathogens. Initial results performed on 150 freeze-dried supernatants highlighted the inhibitory activities of 10 supernatants against *E. amylovora*, 2 against *V. inaequalis*, 4 against *P. aeruginosa* and 1 against *E. coli*. Four of the most active strains were selected for production optimisation and large-scale cultivation leading to bioguided fractionation. The results of this fractionation to isolate bioactive compounds will be discussed.

**Keywords:** antimicrobial resistance, biocontrol, lichen microflora, bioguided fractionation, *Rhizocarpon geographicum*.

**References**

Despotovic, M. et al. (2023) ‘Reservoirs of antimicrobial resistance in the context of One Health’, *Current Opinion in Microbiology*, 73, p. 102291.

González-Domínguez, E., Armengol, J. and Rossi, V. (2017) ‘Biology and Epidemiology of Venturia Species Affecting Fruit Crops: A Review’, *Frontiers in Plant Science*, 8, p. 1496.

Miral, A. et al. (2022) ‘*Rhizocarpon geographicum* Lichen Discloses a Highly Diversified Microbiota Carrying Antibiotic Resistance and Persistent Organic Pollutant Tolerance’, *Microorganisms*, 10(9), p. 1859.

Murray, C.J.L. et al. (2022) ‘Global burden of bacterial antimicrobial resistance in 2019: a systematic analysis’, *The Lancet*, 399(10325), pp. 629–655.

Piqué, N. et al. (2015) ‘Virulence Factors of *Erwinia amylovora*: A Review’, *International Journal of Molecular Sciences*, 16(6), pp. 12836–12854.

<footnote><sup>a</sup> Univ. Rennes, CNRS, ISCR – UMR 6226, 35043 Rennes, France.</footnote>

<footnote><sup>b</sup> Greencell, Biopole Clermont Limagne, 1 Rue Henri Mondor, 63360 Saint-Beauzire, France</footnote>

<footnote>* Presenting author. E-mail address: flavia.bollaro@univ-rennes.fr (Flavia Bollaro).</footnote>