Cyanobacteria Sancta: diversity of oxyphotoprokaryotes on facades of centenary churches in a tropical region of Brazil

Abstract

Aerophytic phototrophic biofilms, predominantly composed of cyanobacteria, are known to affect historical building facades and external structures, potentially causing aesthetic and structural damage. While cyanobacteria are recognized as early colonizers of rocky substrates, their diversity and role in tropical regions, particularly in Brazil, remain underexplored, leading to gaps in taxonomy and a limited understanding of these communities. This study aimed to characterize the cyanobacterial communities at centenary heritage sites using morphological, structural, and molecular techniques. Using qualitative and quantitative data, samples were collected from five churches in Olinda's historic area (PE, Brazil), a nationally recognized heritage site. The analysis included a) inoculum culture, b) morphological characterization, c) ultrastructural examination, and d) phylogenetic analysis (16S rRNA gene sequencing). A total of 36 morphospecies were identified and distributed across 21 genera, with Scytonema schmidtii being the most abundant species in all sampled churches. Scanning electron microscopy revealed a heterogeneous distribution and dominance of coccoid and heterocytous cyanobacteria on the substrates. Molecular analysis of isolated strains identified five distinct lineages, each belonging to a different family, suggesting the presence of potential new species and genera. This study highlights the significant cyanobacterial diversity on these historical substrates and underscores the importance of employing a multi-faceted approach to characterize these biofilms effectively.