Message - 7th IAL Symposium

Lichen: from genome to ecosystem in a changing world
3I-O
(3I-05) Submission ID: IAL0009-00008
ALLELOPATHIC EFFECTS OF LICHEN SECONDARY METABOLITES AGAINST POTENTIAL
COMPETITORS FOR ROCK SURFACES
Favero-Longo S. E. 1 , Gazzano C. 1 , Piervittori R. 1
1 Dip. Biologia Vegetale, Università di Torino, Torino, Italy
Lichen secondary metabolites (LSM) are known to determine allelopathic effects on soil and mycorrhizal
fungi, and on the spore/seed germination and early growth stages of bryophytes and vascular plants, thus
likely supporting the competition of terricolous lichens for soil surfaces. In the current study, laboratory and field
assays were performed to evaluate the potential allelopathic effects of LSM against potential competitors of saxicolous
lichens for rock surfaces. Usnic acid, norstictic acid and parietin, solubilized in water, water-acetone 90:10
mixture and pure acetone, were tested against microcolonial fungi (MCF: Coniosporium apollinis, C. perforans,
C. uncinatum, Phaeococcomyces cfr. chersonesus), black yeasts (BY: Sarcinomyces petricola), green algae
(GA: Apatococcus lobatus, Scenedesmus ecornis) and cyanobacteria (CY: Pleurocapsa minor, Lyngbya sp.).
The common biocide benzalkonium chloride (1%) was used as positive control. Fungal, algal and cyanobacterial
colonies, cultured on standard media (MEA, Trebouxia-Medium, BG11), were poured with 50 μl of each solution
and their areal growth was monitored for one month using image analysis (WinCAM software). Field assays on
black patinas on the walls of the Roman Theatre of Aosta (NW-Italy) were also performed, using epifluorescence
microscopy to check the algal and cyanobacterial sensibility. The different MCF species showed a slightly different
sensibility to the different LSM solutions, but in all the cases the three metabolites in the water-acetone
mixture (ca. 0.05 mM) and usnic acid in water (0.02 mM) determined the highest growth inhibition, displaying
the same effects of benzalkonium chloride. On the other hand, all the LSM solutions did not significantly affect
or even increased the areal growth of algal and cyanobacterial colonies. Epifluorescence observations of the
treated photosynthetic microorganisms in laboratory confirmed that most of cells were still emitting a strong red
fluorescence. However, in the field patinas, algal and cyanobacterial cells showed a higher sensibility to LSM,
more often displaying an epifluorescence decrease in the treated areas with respect to negative controls. In conclusion,
LSM may play a significant role in lichen competition for rock surfaces. LSM may be a potential resource
for the MCF control on rocks, avoiding the use of human-toxic biocides.
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