Colonization Ability of Bacillus subtilis NCD-2 in Different Crops and Its Effect on Rhizosphere Microorganisms

Suppressiveness of spent mushroom substrate amendment against eggplant Verticillium wilt

BACKGROUND

Verticillium wilt, caused by Verticillium dahliae, is a devastating soil-borne disease. Spent mushroom substrate (SMS) has shown potential as a soil amendment for controlling soil-borne diseases. However, the mechanisms underlying its disease-suppressive effects remain poorly understood. Here, the efficacy of SMS in suppressing eggplant Verticillium wilt and mechanisms related to rhizosphere microbiome regulation were investigated.

RESULTS

We tested different SMS sources (Pleurotus ostreatus, Hypsizygus marmoreus, Lentinus edodes), particle sizes (45, 75, 150, 300 μm), and addition ratios (0.5-8%, w/w). The fungus control efficacy ranged from 26 to 66%, with best results from 2% SMS of L. edodes at 150 μm. This treatment resulted in 5.7-fold reduction in the Verticillium dahliae population in eggplant rhizosphere. Eggplant fresh and dry weights of shoots and roots, and plant height, significantly increased with 2% SMS amendment. 16S rDNA sequencing revealed alterations in rhizosphere bacterial communities, with an increase in indigenous beneficial bacteria, particularly Bacillus spp., following SMS amendment. Spent mushroom substrate co-inoculated with exogenous biocontrol strain Bacillus subtilis NCD-2 achieved a synergistic effect against Verticillium wilt than both SMS or NCD-2 alone.

CONCLUSIONS

Results revealed that SMS protects eggplants against Verticillium wilt, largely by recruiting Bacillus spp. to the rhizosphere. The enrichment effect of indigenous Bacillus spp. in the rhizosphere mediated by SMS similarly applies to Bacillus inoculum, enhancing its efficacy in controlling eggplant Verticillium wilt. These findings enhance our understanding of the protective effects of SMS and its role in the biocontrol of Verticillium wilt. © 2025 Society of Chemical Industry.

Defense Responses Stimulated by Bacillus subtilis NCD-2 Through Salicylate- and Jasmonate-Dependent Signaling Pathways Protect Cotton Against Verticillium Wilt

Bacillus subtilis NCD-2 demonstrates exceptional biocontrol potential against cotton Verticillium wilt. While previous studies have established its direct antifungal activity (e.g., inhibiting Verticillium dahliae mycelial growth and spore germination), our work reveals a novel mechanism: NCD-2 primes systemic resistance in cotton by activating plant immune-signaling pathways. Firstly, transcriptional profiling uncovered that NCD-2 triggers a defense response in roots analogous to V. dahliae infection, allowing cotton to maintain a more balanced state when confronted with pathogen attacks. Meanwhile, the mutant strains ∆fen and ∆srf-defective in lipopeptide synthesis-also improved cotton resistance to Verticillium wilt by activating partially identical defense pathways in cotton roots. Furthermore, the application of lipopeptide compounds derived from NCD-2, particularly surfactin and fengycin, could enhance host resistance to V. dahliae. Using an RT-qPCR approach, we found that numerous resistance-related genes were induced by these lipopeptide compounds. The up-regulation of SA/JA pathway markers (e.g., NPR1, ICS1, COI1, and LOX1) revealed NCD-2's activation of plant immune signaling. Using virus-induced gene silencing (VIGS), we conclusively linked SA and JA signaling to NCD-2-induced defense priming. Silencing either pathway abolished resistance, highlighting their indispensable coordination. By bridging mechanistic insights and agricultural applicability, our work positions NCD-2 as a sustainable alternative to conventional fungicides, addressing both crop productivity and environmental health.

Arabinose Plays an Important Role in Regulating the Growth and Sporulation of Bacillus subtilis NCD-2

A microbial fungicide developed from Bacillus subtilis NCD-2 has been registered for suppressing verticillium wilt in crops in China. Spores are the main ingredient of this fungicide and play a crucial role in suppressing plant disease. Therefore, increasing the number of spores of strain NCD-2 during fermentation is important for reducing the cost of the fungicide. In this study, five kinds of carbon sources were found to promote the metabolism of strain NCD-2 revealed via Biolog Phenotype MicroArray (PM) technology. L-arabinose showed the strongest ability to promote the growth and sporulation of strain NCD-2. L-arabinose increased the bacterial concentration and the sporulation efficiency of strain NCD-2 by 2.04 times and 1.99 times compared with D-glucose, respectively. Moreover, L-arabinose significantly decreased the autolysis of strain NCD-2. Genes associated with arabinose metabolism, sporulation, spore resistance to heat, and spore coat formation were significantly up-regulated, and genes associated with sporulation-delaying protein were significantly down-regulated under L-arabinose treatment. The deletion of msmX, which is involved in arabinose transport in the Bacillus genus, decreased growth and sporulation by 53.71% and 86.46% compared with wild-type strain NCD-2, respectively. Complementing the mutant strain by importing an intact msmX gene restored the strain's growth and sporulation.