Message - 7th IAL Symposium

The 7th International Association for Lichenology Symposium 2012
4B: Lichen symbionts and ecophysiology
(4B-P1) Submission ID: IAL0009-00009
A QUANTITATIVE EVALUATION OF BIOCIDE EFFICACY THROUGH THE COLOUR BASED
IMAGE ANALYSIS OF ALGAL CHLOROPHYLL EPIFLUORESCENCE
Favero-Longo S. E. 1 , Gazzano C. 1 , Fusconi A. 1 , Piervittori R. 1
1 Dip. Biología Vegetale, Università di Torino, Torino, Italy
Epifluorescence microscope observations are applied in the field of stonework conservation to semiquantitatively
evaluate the efficacy of biocide treatments on epilithic photoautotrophic organisms, including lichens.
In the current study, dominant lichen species on the marble and calcschist balustrade of the Savoy Castle
in Govone (NW-Italy) were investigated for their sensitivity to the common biocide benzalkonium chloride (BZC).
Five species (Aspicilia contorta, Caloplaca citrina, Candelariella aurella, Protoparmeliopsis muralis, Verrucaria
gr. nigrescens) were assayed with different concentrations (0.5%, 2.5%, 5.0% BZC in isopropanol-water 1:1
mixture), application methods (brushing, spraying) and number of applications (one or two, spaced one week
apart). Epifluorescence observations were performed 8 and 16 days after the treatments. Three representative
images per sample (three samples per species per treatment) were analyzed (a) semi-quantitatively, an expert
eye defining the algal sensitivity according to a 5-level arbitrary scale, and (b) quantitatively, using colour-based
image analysis (WinCAM software). For each image, we determined the hue, saturation and intensity co-ordinates
(colour model HSI) of the epifluorescence of six algal cells arbitrarily chosen using a grid. A high linear
fit was detected between the semi-quantitative data and the hue measures. Spraying gave better results than
brushing. Single and double treatments with 2.5% and 5.0% BZC showed similar efficacy, and this latter was
only slightly higher than that of two applications of 0.5% BZC. A. contorta and P. muralis were highly sensitive
to all the BZC concentrations, while C. citrina, C. aurella and V. muralis showed some resilience also to 5.0%
BZC. In conclusion, the image analysis approach allows the quantitative/statistical comparison of the efficacy of
different treatments avoiding the subjective step of the expert evaluation, suggesting that its application could
extend to the non-expert personnel involved in restoration programs. A comparison of image analysis results
with measurements on the functionality of the photosynthetic process (Chl-a F) of the treated thalli could allow,
in the future, the definition of the range of hue values corresponding to active and inactive algal cells. This step
may further increase the potency of this diagnostic tool and support a progressive reduction of excessive biocide
dispersion in the environment.
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4B-P