Microbial activity and subsistence in oligotrophic lake sediments

In marine and lake sediments the main limitation of microbial activity is the amount and quality of energy and carbon sources, which quickly decline with depth. While deeper sediment communities still contain microbial populations that once inhabited the surface layers, it remains an open question which of them remain metabolically active and which fall 'dormant'. To address this question, we are studying the functional potential and gene expression of microbial populations (represented by metagenome-assembled genomes) from the sediments of oligotrophic lake Lucerne, in a framework of a larger project studying biogeochemical cycles and microbial communities in sediments of five Swiss lakes. Depth profiles of the microbial community composition showed that supposedly aerobic microorganisms can still be found in anoxic sediment layers. In order to test if deeply buried and potentially 'dormant' microorganisms could return to their original surface layer metabolism, we incubated ~2000 years old sediment in diffusion chambers buried in surface sediment for six months. The transcriptomes will reveal if there were changes in gene transcription in any of the populations and at what time during the incubation these changes occurred.