Freshwater cyanobacteria, identified by microscopic and molecular investigations on a colonized fountain surface: a case study in Palermo (Sicily, Italy)

Abstract

Cyanobacteria or blue algae are ubiquitously present in both fresh and brackish water environments. They also grow in conditions of high humidity, colonizing stones or monuments and fountain surfaces, and creating thick biofilms able to induce biodeterioration in the constituent materials of artefacts. As well as several photoautotrophic organisms, cyanobacteria belong to the microorganisms identified as primary colonizers, playing an important role in stone artwork deterioration. In this study, an analysis was made of the biofilm collected from the stone fountain of the Two Dragons in Palermo (Italy), revealing the presence of cyanobacterial colonies by optical microscopy, due to their peculiar auto-fluorescence. Furthermore, molecular investigations by qPCR (quantitative Polymerase Chain Reaction) were utilized to gather quantitative information, and phylogenetics analysis was used to confirm the Thioredox- in reductase (TrxR) gene as a suitable molecular marker. The results highlight the presence of cyanobacteria as the main taxa, whose growth is induced by microclimatic and environmental conditions, and by the physical characteristics of the stone surface. Identification of microbial populations living on stone artworks is the starting point for successful control and conservation strategies, which can help to define the correct protocols to block cellular activity and to find appropriate methods for removing biofilm, as well as counteracting possible recolonization.