Soil microbial gene expression over one year of human decomposition.

During terrestrial vertebrate decomposition, host and environmental microbial communities work together to drive biogeochemical cycling of carbon and nutrients. These mixed communities undergo dramatic restructuring in the resulting decomposition hotspots. To reveal the succession of the active microbes (bacteria, archaea, and fungi) and the metabolic pathways they use, we generated metatranscriptomes from soil samples collected over 1 year from below three decomposing human bodies. Soil microbes increased expression of heat shock proteins in response to decomposition products changing physiochemical conditions (i.e. reduced oxygen, high salt). Increased fungal lipase expression identified fungi as key decomposers of fat tissue. Expression of nitrogen cycling genes was phased with soil oxygen concentrations: during hypoxic soil conditions, genes catalyzing N-reducing processes (e.g. hydroxylamine to nitric oxide and nitrous oxide to nitrogen gas during reduced oxygen conditions) were increased, followed by increased expression of nitrification genes once oxygen diffused back into the soil. Increased expression of bile salt hydrolases implicated a microbial source for the high concentrations of taurine typically observed during vertebrate decomposition. Collectively, microbial gene expression profiles remained altered even after 1 year. Together, we show how human decomposition alters soil microbial gene expression, revealing both ephemeral and lasting effects on soil microbial communities.