Multiwalled Carbon Nanotubes Promoted Biofilm Formation and Rhizosphere Colonization of Bacillus subtilis Tpb55

Plant growth-promoting bacteria (PGPB) achieve effective colonization by forming a biofilm on the root surface. However, the promoting effects and mechanisms of nanomaterials on PGPB biofilm formation and rhizosphere colonization are rarely studied. This study investigated the effects and the potential mechanism of multiwalled carbon nanotubes (MWCNTs) on biofilm formation and rhizosphere colonization of PGPB Bacillus subtilis. 10 and 100 mg/L MWCNTs increased biofilm biomass, extracellular polymeric substance components, live/dead cell ratio, and spores in biofilms. MWCNTs induced B. subtilis Tpb55 upregulated gene expressions of malL, sacX, tasA-tapA, and epsA-O correlated with carbohydrate metabolism and biofilm formation. MWCNTs first stimulated Tpb55 flagellar motility and then increased biofilm formation, thus promoting colonization in the tobacco rhizosphere. Greenhouse experiments showed that the combination of MWCNTs and Tpb55 reduced the occurrence of tobacco black shank. Therefore, MWCNTs have broad application potential in enhancing the effectiveness of PGPB in agricultural disease control and yield enhancement.