Planktonic bacterial motility mediates dissolved organic matter transformation in inland waters: Insights from metatranscriptomics and carbon isotopic evidence.

Microorganisms are pivotal drivers of dissolved organic matter (DOM) transformation in aquatic ecosystems. Despite well-defined stepwise microbial DOM processing via the microbial carbon pump framework, the role of key microbial behavioral traits (e.g., bacterial motility) in regulating DOM biogeochemical processes remains poorly constrained. Based on a field survey of China's diverse inland aquatic habitats, this study integrated DOM molecular characterization, microbial metatranscriptomics, and carbon stable isotope analysis to address this knowledge gap. Our field observations reveal strong covariation between planktonic bacterial motility and DOM molecular properties. Specifically, elevated transcription of motility-related genes correlates with higher mass-to-charge ratio and double-bond equivalent, and lower H/C ratio of DOM molecules. Metatranscriptomic analyses further corroborate the close linkage between bacterial motility and central carbon and energy metabolism. At the community level, keystone proteobacterial taxa are predominantly associated with motility-related transcriptional patterns that covary with altered DOM molecular attributes and shifts in δ¹ ³C signatures of dissolved inorganic carbon. Our findings propose a conceptual framework linking bacterial motility to DOM cycling, highlighting motility as a key modulator of microbial carbon transformation in inland waters.