A research team with lead author Helena Osterholz of the Leibniz Institute for Baltic Sea Research (IOW) reports in the latest issue of the journal Nature Communications on possible pathways by which microbial communities in the nutrient-poor "deep biosphere" can ensure survival. Among others, dissolved organic matter (DOM) was investigated in different deep groundwaters. Their results show that in the uppermost layers of the bedrock most of the labile matter is converted. Below that, mixing processes dominate. The remaining refractory DOM leads to the selection of a core microbiome that can feed on this hard-to-digest food.