Algae and cyanobacteria on painted surfaces in southerns Brazil

Algae and cyanobacteria disfigure the external surfaces of buildings and may cause their physico-chemical deterioration. Even though the climate in Brazil is humid, there is no published literature on this problem. The objective of this work was to identify the major photographs present on Brazilian constructions in residential, urban and rural sites. The algal and cyanobacterial types present on discolored surfaces of painted buildings in nine different municipalities in Brazil, all lying between latitudes 19§ South and 30§South, were examined. A total of 816 different organisms was detected in 58 sites. Approximately 63 (per cent) were single-celled or colonial organisms. The cyanobacterial genus, Synechocystis, was the most biodiverse and frequently comprised the major biomass. It was present in 63,4 (per cent) of sites. Second and third most frequently detected were Oscillatoria and the algal genus, Chorella, respectively. The latter organism showed the most widespread occurrence (72.4 per cent). Cyanobacteria were the most important colonizers, especially at urbans sites, where over 62 (per cent) of the organisms detected belonged to this class. Filamentous photographs were found in smaller numbers than non-filamentous at all locations.

A theoretical model describing the influence of diffusion on microbidal action in biofilms

Um dos métodos padröes para avaliar a atividade de um microbicida é a medida da taxa de morte de células sésseis ou em suspensäo (planctônicas). Sabe-se que, na maioria dos casos, células sésseis säo mais resistentes às substâncias inibidoras do que as células planctônicas. Este aumento de resistência pode ser devido à mudança na fisiologia das células ou à falta de penetraçäo do microbicida no biofilme. Um modelo que demonstra a influência da taxa de penetraçäo de microbicidas sobre a morte das células é apresentado. Os cálculos podem ser feitos por computador utilizando-se programas de planilhas eletrônicas. Os resultados mostram que o biofilme reduz a taxa de morte das células, quando a fisiologia microbiana näo é alterada. Pelo modelo, pode-se estimar a concentraçäo de microbicida necessária para matar tanto células sésseis quanto células em suspensäo, no mesmo estado fisiológico, num tempo