1-Aminocyclopropane-1-Carboxylate: A Novel and Strong Chemoattractant for the Plant Beneficial Rhizobacterium UW4.

Plant growth-promoting rhizobacteria (PGPR) and fungi-bacterial biofilms are both important biofertilizer inoculants for sustainable agriculture. However, the strongest chemoattractant for bacteria to colonize the rhizosphere and mycelia is not clear. Coincidentally, almost all the PGPRs possess 1-aminocyclopropane-1-carboxylate (ACC) deaminase (AcdS) and can utilize ACC as the sole nitrogen source. Here, we found that ACC was a novel, metabolic dependent and methyl-accepting chemoreceptor-involved chemoattractant for UW4. The chemotactic response of UW4 to ACC is significantly greater than that to the amino acids and organic acids identified in the plant root and fungal hyphal exudates. The colonization counts of the UW4 or deletion mutants in the wheat rhizosphere and on mycelia were reduced one magnitude compared with those of UW4. The colonization counts of UW4 on antisense ACC oxidase mycelia with a high ACC production significantly increased compared with , followed by the UW4 complementary strain and the ethylene chemoreceptor gene-deletion mutant. The colonization counts of the UW4 strains on mycelia with a low ACC production decreased significantly compared with wild type. These results suggested that ACC and not ethylene should be the strongest chemoattractant for the PGPR that contain AcdS.