oa Naturally Occurring Hydrogen Isotope Composition of Microbial Lipids: Toward Group-Specific Carbon Use Efficiency in Soils

Microbial activity is an essential part of carbon cycling in soils. A common descriptive method is the community-level carbon use efficiency (CUE), which indicates if carbon is preferentially being stored or respired. Resolution on the specific microbial groups and their activity behind CUE not only improve our mechanistic understanding, but also enable a better monitoring following disturbances and/or management strategies.

The current methods mostly rely on the addition of labelled substrates, thus potentially influencing targeted activity. The hydrogen isotopic composition of microbial phospholipid fatty acids (PLFAs) are naturally strongly associated with the metabolism of active bacteria and could be used to assess group-specific CUE.

In order to assess the potential of H isotope composition of PLFAs for group-specific CUE, we need to investigate how robust they are related to variables (e.g. co-cultures, low/high substrate concentration, mixture of substrates). Interactions between bacteria such as substrate-competition and direct antagonism (e.g. production of antibacterial compounds) could influence d2HPLFAs and obscure the clear association observed with the central metabolism in pure cultures. As a first step, we therefore investigate the effect of co-cultivating Pseudomonas and Bacillus on the 2H-signature of their respective PLFAs.