Biocide-Containing facades alter culture-based bacterial and fungal community composition and resistance patterns to octylisothiazolinone

Microbial communities are known to colonize biocide-free (BFFs) and even biocide-containing façades (BCFs) under various environmental conditions, leading to loss of value of façades due to biologically caused aging and discoloration. The first objective of this study was to characterize the bacterial and fungal cultivation-based communities present on BCFs and BFFs after one year of outdoor exposure. The second objective was to assess their tolerance to biocide octylisothiazolinone (OIT), which was only present on the BCFs. Culture-based analysis revealed significant differences in bacterial community composition between the BFFs and BCFs. Fungal isolates also varied, with Penicillium predominantly found on the BCFs and Vishniacozyma and Memnoniella on the BFFs. MIC testing showed that the isolates from the BCFs exhibited slightly higher tolerance to OIT than those from the BFFs, although the differences were not statistically significant. Notably, several bacterial genera identified in both façade types - Clavibacter, Micrococcus, Nocardioides, Rhodococcus, and Streptomyces - as well as the fungal genus Penicillium, have previously been reported to degrade biocides. These findings demonstrate that both BF and BC façades support taxonomically diverse and resilient microbial communities within a relatively short exposure period. While minor shifts in biocide tolerance were observed, the lack of significant differences suggests that microbial adaptation to biocide-containing façades may be more complex and gradual, underscoring the need for time-resolved and functional studies to better understand microbial adaptation to biocide in façades.