N-216. An Analysis of Bacterial and Fungal Biofilms Inhabiting Concrete Surfaces

D. J. Giannantonio, J. C. Kurth, K. E. Kurtis, P. A. Sobecky;
Georgia Inst. of Technology, Atlanta, GA.

The formation of biofilms on concrete surfaces can have deleterious effects both on a structure’s aesthetic appeal and integrity. The objective of this study is to examine the biofilms that form on outdoor concrete structures in order to determine their community composition, requirements for formation, and relative success and effects on concrete of differing compositions and physical characteristics. Biofilm community composition was examined by generating and analyzing clone libraries of 16S and internal transcribed spacer (ITS) ribosomal DNA extracted from biofouled concrete surfaces sample sites throughout Georgia, USA. Physical and chemical characteristics of concrete at the sites, such as compressive strength, permeability, and surface carbonation depth, were measured and compared to relative biofilm coverage. Biofilm formation was then examined utilizing rain simulation chambers capable of spraying (and recycling) media onto inoculated concrete tiles. This system was used to test culturable isolates from the sample sites and concrete tiles cast with varying compositions. Different media (potato dextrose broth, purified water, and sterilized rainwater) and the presence of artificial sunlight were also tested. Analysis of clone library sequences revealed a variety of beta and gammaproteobacteria as well as a number of fungal genera, including Cladosporium, Hypocrea, and Alternaria. Of the concrete characteristics analyzed for each of the sites, only the presence of an acrylic paint coating showed positive correlation to biofilm coverage. Growth experiments required media with a substantial nutrient source (potato dextrose broth) for biofilm formation on the concrete tiles. Also, biofilm formation showed a positive correlation with tile surface roughness, and inhibition on cement containing TiO₂ exposed to artificial sunlight. This study concludes that concrete biofilms are composed of a variety of bacteria and fungi that require nutrients not provided on the concrete proper to grow, and that biofilm formation can be influenced by the composition and physical properties of the concrete surfaces they inhabit.