Ethanol exposure is associated with spatial and taxon-specific gut microbiota remodeling characterized by ecological adaptation rather than broad activation of microbial ethanol metabolism.

Alcohol-associated diseases are linked to gut microbiota disruption, but how ethanol intake is associated with microbial functional remodeling remains unclear. Here, using male C57BL/6J mice, we integrated spatiotemporal quantification of ethanol and acetaldehyde across the gastrointestinal tract with 16S rRNA sequencing, metagenomics, metaproteomics, and metabolomics. Our results showed that small-intestinal communities were enriched in taxa and functions related to bile acid tolerance/utilization, whereas cecal communities exhibited pronounced remodeling of multiple core functions associated with ecological adaptation. Although the abundance of several ethanol metabolism-related genes increased, this genetic potential was not broadly translated into detectable protein-level activation. Ethanol metabolism-related proteins were mainly derived from Lachnospiraceae, whose metabolic activity was suppressed. In contrast, Muribaculaceae, Desulfovibrionaceae, and Barnesiellaceae gained functional advantages in substrate acquisition, energy metabolism, oxidative stress defense, and proteostasis. These findings provide a region-resolved functional map indicating that ethanol-associated microbiota remodeling is characterized by ecological adaptation, rather than uniform activation of direct microbial ethanol metabolism.