Message - 7th IAL Symposium

The 7 th International Association for Lichenology Symposium 2012
(1A – O11) Submission ID: IAL0212-00002
THE LICHEN KILLER: WHEN STONE CONSERVATION ASKS FOR NEW METHODS
OF LICHEN DEVITALIZATION
Bertuzzi S. 1 , Candotto Carniel F. 1 , Tretiach M. 1
1 Dipartimento di Scienze Della Vita, Università degli Studi di Trieste, Trieste, Italy
The pros and cons of a new approach for killing poikilohydrous photoautotroph organisms that colonize
outdoor stone buildings are discussed on the basis of field and laboratory data. The control of biological growth,
particularly important in the field of stone conservation, largely depends on the use of biocides, that may be
dangerous for the workers, the environment and the substratum. The new approach makes the most of a poorly
known peculiarity of poikilohydrous organisms: they are thermo-tolerant (up to 55-60°C) when inactive for lack
of water, but thermo-sensitive when hydrated and fully active metabolically. The efficacy of thermal treatments
(range: 35-50°C), in parallel to applications of three commercial biocides based on quaternary ammonium cations
and n-octyl-isothiazolinone, was verified in the laboratory with the biodeteriogenous lichens Protoparmeliopsis
muralis and Verrucaria nigrescens at various water contents. Chlorophyll a fluorescence (ChlaF) emission
were checked in treated and non-treated samples at different time intervals, from 12 h to 16 days, whereas confocal
laser scan microscopy in combination with fluorescent dyes was used to assess the physiological state of
photobiont and mycobiont cells. Further ChlaF measurements were carried out outdoor to evaluate the feasibility
of treatments against biofilms of rocky outcrops and walls, and the behavior of phylogenetically distant groups,
from cyanobacteria, to microalgae and bryophytes. The results confirm that treatments of 12-24 hours at 40-
45°C are sufficient to kill all the colonizers tested so far if they are kept fully hydrated. At 35-40°C the organisms
are damaged: in this case biocides at concentrations from ten to one hundred times lower than in normal applications
can be used for killing them. The new protocol is simple, the field equipment is cheap, the negative
effects associated with the standard biocide treatments are virtually absent, and there is no interference with the
substratum. The application of thermal treatments in the tropics is also discussed.
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1A-O