Nd-YAG laser irradiation damages to Verrucaria nigrescens

Epilithic and endolithic microorganisms and lichens play an important role in stone biodeterioration. The structural and physiological damage caused by nanosecond pulsed laser of 1064 nm from Nd:YAG laser to Verrucaria nigrescens lichen as well as to endolithic algae and fungi were investigated in the present study. Ultrastructural laser effects on lichen and endolithic microorganisms were study without disturbing the relationship between lichen and lithic substrate by taking lichen-containing rock fragments and processing both together. SEM-BSE, LT-SEM and FM were used to determine cell integrity and ultrastructure, which reflect microorganism viability. Photobiont vitality was determined using a PAM chlorophyll fluorescence technique. The lichen thalli were completely removed by irradiation with 5 ns pulses at a fluence of 2.0 J/cm2 with no stone damage as showed by micro-Raman spectroscopy. The fungal and algal endolithic cells located below were completely destroyed or presented a high plasmolysis degree resulting from heating their microenvironment. The lichen and endolithic mycobiont near the irradiated zone were also damaged. Algal photosynthetic damage prevents fungal survival and lichen viability. This is the first report of laser removal and inactivation of lichen and lithic microorganisms, and thus provide an environmentally friendly and efficient method to control stone biodeterioration.Work funded by MICINN under Projects CTM2009-12838-CO4-O3, CTQ2010-15680 and CGL2010-16004, and CONSOLIDER CSD2007-00058, and the Programa Geomateriales (CAM, S2009/Mat-1629).Peer reviewe