Diversity of salt-tolerant culturable aerobic microorganisms on historic buildings in Southern Brazil

Abstract

Halotolerant and halophilic microorganisms may be expected to be present on the external walls of buildings, especially in dry and/or hot climates. They have been detected in Europe in various molecular biological studies. Using plating on specific salt-supplemented medium (10 and 15%), bacteria and fungi were detected in winter, spring and summer months on the discoloured external walls of 5 historic buildings in Porto Alegre, South Brazil. Microbial biodiversity in the samples was calculated using the Simpson Index. Halotolerant non-phototroph diversity was highest in the winter (September), when environmental conditions are less extreme. Some collections yielded organisms that grew on media with 15% added salt; diversity in this case was lower. Frequently, and in all winter collections, only one type of microorganism grew; this was a brown-pigmented fungus, probable genus Cladosporium. Greater diversity was found at 15% salt in 2 collections made in the summer month of January. It is suggested that this results from the selection of organisms able to resist the more extreme conditions of high temperature and lower relative humidity.