Novel enhanced network integrating transformations of DOM and microorganisms (ENITM) elucidates microbial-driven...

Estuary sediments have complex and dynamic organic composition, is an important organic carbon reservoir. Revealing the molecular composition and biogeochemical transformation of the dissolved organic matter (DOM) in estuary sediments is key to understand estuary carbon turnover at the mechanistic level. This study analyzed sediments collected in a river-to-ocean continuum, revealing the dynamics of both DOM and microbial community. Results show that salinity, pH, and the carbon-to-nitrogen (C/N) ratio significantly influence the composition, functionality, and co-occurrence patterns of the sedimental microbial communities as well as the molecular composition of sedimental DOM. DOM in river sediments display higher aromaticity, greater average molecular weight, and higher molecular diversity than ocean sediments. In particular, we improved and developed an enhanced networks by integrating DOM molecular transformations and microorganism (ENITM) to explore the possible microbial-driven mechanism of DOM transformation. The varying contributions of different microbes to the transformation of various DOM molecules and the potential transformation pathways of various DOM molecules are revealed through ENITM. Two potentially microbial transformation pathways involved were identified: substitution or addition of aromatic structure and incorporation of guanidine-related moieties. This new strategy will help to explore the role of microorganisms in the transformation of natural organic matter, and can be applied in other ecosystems in the future.