Linking Microbial Community Structure, Activity and Carbon Cycling in Biological Soil Crust

Soils play a key role in the global carbon cycle, but the relationships between soil microbial communities and metabolic pathways are poorly understood. In this study, biological soil crusts (biocrusts) from the Colorado Plateau are being used to develop soil metabolomics methods and statistical models to link active microbes to the abundance and turnover of soil metabolites and to examine the detailed substrate and product profiles of individual soil bacteria isolated from biocrust. To simulate a pulsed activity (wetting) event and to analyze the subsequent correlations between soil metabolite dynamics, community structure and activity, biocrusts were wetup with water and samples (porewater and DNA) were taken at various timepoints up to 49.5 hours post-wetup. DNA samples were sequenced using the HiSeq sequencing platform and porewater metabolites were analyzed using untargeted liquid chromatography/ mass spectrometry. Exometabolite analysis revealed the release of a breadth of metabolites including sugars, amino acids, fatty acids, dicarboxylic acids, nucleobases and osmolytes. In general, many metabolites (e.g. amino acids and nucleobases) immediately increased in abundance following wetup and then steadily decreased. However, a few continued to increase over time (e.g. xanthine). Interestingly, in a previous study exploring utilization of soil metabolites by sympatric bacterial isolates from biocrust, we observed xanthine to be released by some Bacilli sp. Furthermore, our current metagenomics data show that members of the Paenibacillaceae family increase in abundance in late wetup samples. Previous 16S amplicon data also show a "Firmicutes bloom" following wetup with the new metagenomic data resolving this at genome-level. Our continued metagenome and exometabolome analyses are allowing us to examine complex pulsed-activity events in biocrust microbial communities specifically by correlating the abundance of microbes to the release of soil metabolites. Ultimately, these approaches will provide an important complement to sequencing efforts linking soil microbes and soil metabolites to enable genomic sciences approaches for understanding and modeling soil carbon cycling.