Structural diversity of photoautotrophic populations within the UNESCO site ‘Old Cathedral of Coimbra’ (Portugal), using a combined approach

In 2013, UNESCO classified the ‘University of Coimbra – Alta and Sofia’ (Portugal) as World Heritage site. Some of the limestone monuments that compose the site, such as the Old Cathedral of Coimbra, show clear visual effects of biological colonization by cyanobacteria and microalgae. The aim of this study was to thoroughly characterize the structural diversity of the photoautotrophic community at this site, combining isolation and molecular identification with next-generation sequencing techniques. Culture-dependent approaches resulted on the identification of green microalgae belonging to Prasiolales, Chlorellales, Watanabea, Chlamydomonadales and Sphaeropleales clades, and cyanobacteria belonging to Nostocales and Synechococcales clades. Culture-independent methods using Illumina Platform resulted in the identification of 610 Operational Taxonomic Units (OTUs), revealing the presence of populations within phyla Chlorophyta, Cyanobacteria, Rhodophyta and Stramenopiles/Bacillariophyta. In addition, principal component analysis (PCA) and a network analysis were generated and successfully related the different populations to specific biodeterioration scenarios observed at this monument. The use of culture-dependent and -independent techniques together with PCA and network analysis allowed us to understand the distribution patterns of the photoautotrophic community among the different biofilms observed at this monument, as well as their ecological specifications. This study highlights that both cultivation and metagenomics methodologies should be employed synergistically in similar biodeterioration studies.