Bacterial Communities in Concrete Reflect Its Composite Nature and Change with Weathering

Abstract

Concrete is an extreme but common environment and is home to microbial communities adapted to alkaline, saline, and oligotrophic conditions. Microbes inside the concrete that makes up buildings or roads have received little attention despite their ubiquity and capacity to interact with the concrete. Because concrete is a composite of materials which have their own microbial communities, we hypothesized that the microbial communities of concrete reflect those of the concrete components and that these communities change as the concrete ages. Here, we used a 16S amplicon study to show how microbial communities change over 2 years of outdoor weathering in two sets of concrete cylinders, one prone to the concrete-degrading alkali-silica reaction (ASR) and the other having the risk of the ASR mitigated. After identifying and removing taxa that were likely laboratory or reagent contaminants, we found that precursor materials, particularly the large aggregate (gravel), were the probable source of ∼50 to 60% of the bacteria observed in the first cylinders from each series. Overall, community diversity decreased over 2 years, with temporarily increased diversity in warmer summer months. We found that most of the concrete microbiome was composed of Proteobacteria, Firmicutes, and Actinobacteria, although community composition changed seasonally and over multiyear time scales and was likely influenced by environmental deposition. Although the community composition between the two series was not significantly different overall, several taxa, including Arcobacter, Modestobacter, Salinicoccus, Rheinheimera, Lawsonella, and Bryobacter, appear to be associated with ASR. IMPORTANCE Concrete is the most-used building material in the world and a biologically extreme environment, with a microbiome composed of bacteria that likely come from concrete precursor materials, aerosols, and environmental deposition. These microbes, though seeded from a variety of materials, are all subject to desiccation, heating, starvation, high salinity, and very high pH. Microbes that survive and even thrive under these conditions can potentially either degrade concrete or contribute to its repair. Thus, understanding which microbes survive in concrete, under what conditions, and for how long has potential implications for biorepair of concrete. Further, methodological pipelines for analyzing concrete microbial communities can be applied to concrete from a variety of structures or with different types of damage to identify bioindicator species that can be used for structural health monitoring and service life prediction.

Metagenomic analysis of concrete bridge reveals a microbial community dominated by halophilic Bacteria and Archaea

“…These microbes encode pathways that potentially allow them to mitigate the primary selective pressures in concrete, including heavy metal tolerance and a variety of osmotic stress responses. This contrasts with our previous work in much younger concrete (< 3 years old), which used 16S amplicon sequencing to characterize a microbial community composed primarily of generalist, sometimes oligotrophic bacteria, and no detectable Archaea 1 .…”

“…However, it may take years for extreme environments to be colonized by microbes capable of thriving there, and even longer for them to reach detectable levels. We previously found that in the early months of concrete weathering, microbial communities in concrete resembled those of the precursor materials used in the concrete mix 1 . Over two years, the diversity of bacteria decreased and became more similar to the microbial communities associated with the large aggregates and cement powder, potentially indicating that these components share characteristics with concrete.…”

“…Improved yield? (p-value) Longer EDTA wash (10 mM, 48-72 h) followed by previous concrete protocol Previously used protocol for concrete 1 No (p = 0.32) Two EDTA washes ( DNA extraction yields were compared between protocols and between modified or unmodified protocols.…”

“…Concrete is a dry, salty, oxidized, alkaline environment that hosts a small but diverse community of microbes 1,2 . These characteristics make it a harsh environment that presumably imposes strong selective pressures on the microbes in it from the time it is poured, but in our previous work, relatively few known halophilic or alkaliphilic taxa were observed during the first two years after curing 1 . However, it may take years for extreme environments to be colonized by microbes capable of thriving there, and even longer for them to reach detectable levels.…”

Metagenomic insights into the microbial communities of inert and oligotrophic outdoor pier surfaces of a coastal city

“…Unlike indoor surfaces, outdoor surfaces are often exposed to uncontrolled and harsh environmental conditions, such as intense ultraviolet light, fluctuating temperature, desiccation, and poor nutrient supply. These conditions and stressors not only induce esthetic deterioration of the surfaces (e.g., corrosion), but also threaten the survival of microbial residents [ 19 ]. However, some of the microbes can adapt to and survive such stresses by a variety of strategies [ 20 ].…”