Effects of Autoinducer-2 on rumen bacterial community succession during in vitro fermentation with oat and Suaeda salsa straws.

In order to reveal the effect of Autoinducer-2 (AI-2) quorum sensing signal on rumen bacterial community under roughage substrates with significant differences in chemical composition (oat straw has high lignocellulose and low crude protein, Suaeda salsa straw has higher crude protein and soluble carbohydrate content, and ash salt content). In this study, oat straw and Suaeda salsa straw were used as substrates, combined with in vitro batch culture fermentation and AI-2 addition treatment, the changes of bacterial community structure, interaction network, predicted metabolic function and xylanase activity were systematically analyzed. The community structures of the oat straw and Suaeda salsa systems differed significantly, and their disparities amplified across serial subcultures. Regulation of AI-2 on the communities showed obvious substrate dependence: in the oat system, AI-2 significantly reshaped the community structure and increased species diversity, whereas in the Suaeda salsa system, it showed a opposite trend. Network analysis showed that AI-2 treatment reduced community connectivity and increased the proportion of negative correlation edges, indicating that it could affect community stability by reconstructing competition and cooperation among species. Functional prediction and enzyme analysis revealed AI-2 enriched carbon metabolism pathways and raised xylanase activity across both substrates, with distinct regulated metabolic pathways observed in the two substrate cultures. This study provides a new perspective for understanding bacterial community succession regulated by quorum sensing signals in in vitro culture systems.