Degraded concrete road bridge metagenome

Surveys of microbial life in and on concrete have thus far relied on 16S amplicon sequencing or cultured organisms, biasing understanding of these communities toward previously characterized and more readily cultured microbes, while leaving functional and metabolic questions unanswered. Metagenomic analysis can resolve these biases and provide greater taxonomic resolution, as well as functional profiles. We improved DNA extraction from a sample of concrete obtained from a road bridge, and show that this method provides DNA of sufficient quality and quantity to do shotgun metagenomic sequencing. The microbial community was dominated by halophilic bacteria and archaea, with enriched functional pathways related to osmotic stress responses. Prior work found that halophilic bacteria were relatively rare in younger concrete samples, which had abundant oligotrophic taxa. This work suggests that as concrete ages and weathers, nutrient limitation may be alleviated, but salt and/or osmotic stress may become a more important selective pressure.