Metagenomic and morphological analysis of biodeteriogenic biofilms on historic stone buildings in the tropical north-east of Brazil

Samples of dark-colored biofilms collected from the surfaces of three 16th and 18th century buildings in equatorial Brazil, two limestone churches in Salvador, Bahia, and a sandstone fort in Belém, Para, were characterized using metagenomics, light microscopy and field emission scanning electron microscopy (FESEM) with energy-dispersive X-ray spectroscopy (EDS). Cyanobacteria were dominant colonisers, Chroococcidiopsis and Trichotorquatus on Salvador churches, and Aerosakkonema on the Belém fort. Actinomycetes and extremophiles were more common in hotter and more humid Belém than in Salvador. Major fungal sequences represented Sordariomycetes and Dothideomycetes, the latter being more frequent in Belém. The presence of several bacterial species and of the diatom Humidophila contenta are reported for the first time on historic stone buildings. Apart from microbially induced discoloration, biogenic deposits of goethite and possibly pyrite were found within the stone, contributing to its biodeterioration.