Old meets new: most probable number validation of metagenomic and metatranscriptomic datasets in soil

Metagenomics and metatranscriptomics provide insights into biological processes in complex substrates such as soil, but linking the presence and expression of genes with functions can be difficult. Here, we obtain traditional most probable number estimates (MPN) of Rhizobium abundance in soil as a form of sample validation. Our work shows that in the Highfield experiment at Rothamsted, which has three contrasting conditions (>50 years continual bare fallow, wheat and grassland), MPN based on host plant nodulation assays corroborate metagenomic and metatranscriptomic estimates for Rhizobium leguminosarum sv. trifolii abundance. This validation is important to legitimize soil metagenomics and metatranscriptomics for the study of complex relationships between gene function and phylogeny