Long lasting non-cellular reactions in sterilized soils recapitulate most of the intermediates of the Krebs cycle

The oxidation of organic matter to CO 2 in soils, i.e. soil respiration, was traditionally considered to be a strictly intracellular biological process. However, studies over the past decade have revealed that non-cellular organic matter mineralisation is ubiquitous in soils and contributes significantly to CO 2 emissions from soils. Nevertheless, the chemical pathways involved and the metabolite intermediates produced by these non-cellular reactions remain unknown. In the present study, we investigated the long-term fate (> 6 months) of organic substrates supplied to sterilized soils. Our results demonstrate that, when incubated with [U-13C] -glucose and -citrate, a sterilized soil matrix can generate Krebs cycle intermediates, alongside by-products such as acetate and formate. These findings support the hypothesis that non-cellular processes in soil can carry out network reactions that gradually decompose thermodynamically stable organic compounds into various metabolites that can more easily undergo decarboxylation, similar to cellular metabolism.