The effect of time and surface type on the composition of biofilm communities on concrete exposed to seawater

Microbially induced deterioration is a threat to concrete infrastructures in marine environments. Complex microbial biofilms form on concrete surfaces exposed to sea water and cause material deterioration. However, the mechanisms determining the composition and the development of the biofilm communities are poorly understood. We designed a mesocosm experiment to determine the influence of concrete surface structure (smooth/rough) and steel fiber reinforcement (presence/absence) on biofilm development over a period of 455 days. This enabled a novel methodology to systematically assess biofilm formation of bacteria on concrete exposed to marine water. The biofilm communities were distinctly different from the planktonic communities in the systems. The alpha diversity increased with time and longer time intervals correlated with higher turnover of taxa. Several taxa within Caulobacterales and Rhodobacterales were identified as early biofilm formers, which decreased in relative abundance and were replaced by taxa within Planctomycetales as the biofilm developed. Throughout the experimental period, concrete surface type influenced the microbial community composition. Some taxa such as Magnetospiraceae, Portibacter, Rubripirellula, and Rhodopirellula, possibly involved in the oxidation and reduction of iron, were for instance more abundant in biofilms on steel-fiber containing concrete. Null models suggested that mainly deterministic factors were shaping the microbial communities with limited importance of stochasticity at shorter time intervals.