The role of MorI/MorR quorum sensing in Methylobacterium oryzae CBMB20: modulating bacterial functions for enhanced adaptability.

The quorum-sensing (QS) system in Methylobacterium oryzae CBMB20, an endophytic bacterium associated with rice (Oryza sativa L.), plays a critical role in regulating bacterial behaviors essential for plant growth promotion and adaptation. This study aimed to elucidate the functional role of the MorI/MorR QS system in M. oryzae CBMB20 and its potential application as a bioinoculant. We identified and characterized two QS signals, 3-OH-C12-HSL and 3-oxo-C12-HSL, synthesized by the MorI enzyme. The MorR receptor was found to preferentially respond to 3-OH-C12-HSL, indicating a high degree of specificity in QS signaling. The deletion mutants of morI and morR exhibited significant changes in exopolysaccharides (EPS), motility, and methanol utilization, suggesting that the MorI/MorR system is crucial for bacterial survival and adaptation. Transcriptome analysis revealed that MorR acts as a repressor, controlling the expression of numerous genes, many of which are upregulated upon its deletion. Our findings highlight the multifaceted role of the MorI/MorR QS system in M. oryzae CBMB20, influencing key biological functions such as EPS production, motility, and methanol utilization. The modulation of these traits through QS could enhance the bacterium's effectiveness as a bioinoculant for promoting plant growth. This study contributes to the understanding of how QS systems can be harnessed to improve the efficacy of plant growth-promoting bacteria in agricultural settings, offering insights into the potential for genetic manipulation to optimize bioinoculant performance.

Importance: This study provides critical insights into microbial communication by functionally characterizing the MorI/MorR quorum-sensing (QS) system in Methylobacterium oryzae CBMB20, a plant-beneficial methylotroph. We identify 3-OH-C12-AHL as a key long-chain signal governing exopolysaccharides biosynthesis, swimming motility, and methanol metabolism traits pivotal for host colonization. These findings not only elucidate novel regulatory mechanisms in plant-associated bacteria but also pave the way for engineering QS-driven strategies, such as synthetic consortia or targeted microbiome interventions, to enhance sustainable agricultural practices.