Structure and function of bacterial metaproteomes across biomes

Soil microbes, and the proteins they produce, are responsible for a myriad of soil processes which are integral to life on Earth, supporting soil fertility, nutrient fluxes, trace gas emissions, and plant production. However, how and why the composition of soil microbial proteins (the metaproteome) changes across wide gradients of vegetation, climatic and edaphic conditions remains largely undetermined. By applying high-resolution mass spectrometry to soil samples collected from four continents, we identified the most common proteins in soils, and investigated the primary environmental factors driving their distributions across climate and vegetation types. We found that soil proteins involved in carbohydrate metabolism, DNA repair, lipid metabolism, transcription regulation, tricarboxylic acid cycling, nitrogen (N) fixation and one-carbon metabolism dominate soils across a wide range of climates, vegetation types and edaphic conditions. Vegetation type and climate were important factors determining the community composition of the topsoil metaproteome. Moreover, we show that vegetation type, climate, and key edaphic proporties (mainly soil C fractions, pH and texture) influenced the proportion of important proteins involved in biogeochemical cycles and cellular processes. We also found that protein-based taxonomic information based on proteins has a greater resolution than 16S rRNA gene sequencing with regards to the ability to detect significant correlations with environmental variables. Together, our work identifies the dominant proteins produced by microbes living in a wide range of soils, and advances our understanding of how environmental changes can influence the structure and function of the topsoil metaproteome and the soil processes that they support.