ABSTRACT

The Eastern India is a valuable cultural heritage site rich of monuments that represent the past Indian art. These monuments are made up by sandstone or limestone or mortar and are interested by an extensive cover of phototrophic biofilms on the exposed surfaces that caused their disfiguration and biodeterioration (Samad & Adhikary 2008). The biofilms are composed mainly by cyanobacteria in association with bacteria, fungi and some microalgae (Gaylarde et al. 2001, Crispim et al. 2003). The biofilm-forming cyanobacteria are of particular scientific interest due to their survival ability to withstand a variety of stresses like high temperature, high light intensity coupled with extreme dryness. However, they occurred as dried and consequently inactive biofilms on exterior of stone structures during summer but can recover quickly if water is suddenly available after rain events. The dominating stress tolerant cyanobacteria upon these stone monuments of the tropics are filamentous and heterocystous one with thick sheaths that presents UV sunscreen/sun blocking pigments fundamental at these extreme conditions (Adhikary & Sahu 1998, Gupta & Agrawal 2008,

tion to which the stone monuments are exposed represent selective factors for the growth of microorganisms and only these stress tolerant cyanobacteria are able to survive, although in a vegetative state (Samad & Adhikary 2008, Keshari & Adhikary 2013). Stress tolerance is the series of alteration in the organisms at the morphological and molecular levels, due to their adaptation to a changed environment. In order to better understand the biodeterioration process of the stone monuments studies were carried out to characterize the microorganisms present in biofilms collected from a statue and from an Indian Temple. Due to the fact that sometimes temperature exceeds 65°C during summer months, the cyanobacterial response to heat stress has been investigated. In order to develop new non-invasive methodologies for the remediation of these valuable stone monuments a carbon based nanomaterial, the graphene oxide, was tested on the biofilms in order to investigate the potentiality as biocide to be used for the restoration of the valuable surfaces.