Bacillus mojavensis dxk33 Modulates Rhizosphere Microbiome and Suppresses Root Rot in Cunninghamia lanceolata

Soil-borne pathogens cause devastating root rot diseases in forest ecosystems, often by inducing dysbiosis in the rhizosphere microbiome. While antagonistic bacteria can suppress disease, their effects frequently extend beyond direct inhibition to include ecological restructuring of resident microbial communities. However, the causal relationships between such microbiome restructuring and disease suppression in tree species remain poorly understood. Here, we show that the antagonistic bacterium B. mojavensis dxk33 effectively suppresses F. solani-induced root rot in C. lanceolata, and that this disease suppression coincides with a partial reversal of pathogen-associated dysbiosis in the rhizosphere. Inoculation with dxk33 significantly promoted plant growth and reduced the disease index by 72.19%, while concurrently enhancing soil nutrient availability and key C-, N- and P-cycling enzyme activities. High-throughput sequencing revealed that dxk33 inoculation substantially reshaped the rhizosphere microbiome, counteracting the pathogen's negative impact on microbial diversity and coinciding with a shift toward a more stable community structure. Under pathogen stress, dxk33 enriched beneficial bacterial taxa such as Pseudomonas and Sphingomonas and suppressed pathogenic fungi while promoting beneficial fungi such as Mortierella. Linear discriminant analysis and functional prediction further indicated that dxk33 remodeled ecological guilds enriched for mycorrhizal and saprotrophic fungi, and reactivated bacterial metabolic pathways and signaling networks that were suppressed by the pathogen. Taken together, our findings are consistent with a multi-tiered mode of action in which direct antagonism by B. mojavensis dxk33 operates alongside associated changes in the rhizosphere microbiome that resemble a disease-suppressive state, although the present experimental design does not allow a strictly causal role for microbiome reconfiguration in disease suppression to be established. This study provides a mechanistic framework for understanding how microbiome engineering may mitigate soil-borne diseases in perennial trees and highlights the potential of targeted microbial interventions for sustainable forest management.