Bacterial diversity in biofilms on external surfaces of historic buildings in Porto Alegre

Summary Bacteria, along with other microorganisms, are present on and in rocks or historic stone monuments and can cause biodeterioration. Gram-positive bacteria, although present in lower numbers, are principally responsible for the damage caused. Four churches and the Vice-Governor’s office in Porto Alegre, all buildings of historic importance were studied, using traditional microbiological methods, with the aim of assessing the microdiversity on their external surfaces. A large number of microorganisms was found in each biofilm. Cell morphology varied at different points and with season. Most of the gram-positive bacteria were of the Bacillus genus, which are readily able to survive the dry conditions on these exposed surfaces. The isolates with the highest deteriorating ability, producing acids and surfactants with autoemulsifing power, were Bacillus isolates B4, B6 and B10 from Priest groups II, I and III, respectively. These were evaluated.