Beneficial plant-associated microbes such as Bacillus species have important potential uses as bioinoculants that reduce dependence on agricultural chemicals. These microbes produce diverse metabolites that enhance plant resilience, but the functions of these compounds and the associated plant hormone pathways remain unclear. Using Bacillus velezensis ES-120, a novel strain isolated from Chenopodium album L., we demonstrate that distinct classes of ES-120 metabolites play different roles. Using Arabidopsis thaliana, we show that non-volatile soluble metabolites produced by ES-120, including lipopeptides identified by reversed-phase high-performance liquid chromatography, exhibit biocontrol activity by inhibiting multiple soil-borne pathogens. In contrast, volatile organic compounds (VOCs) emitted by ES-120 promote plant growth, likely by modulating auxin and brassinosteroid (BR) signalling pathways, with effects sustained across diverse conditions. Headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry identified multiple VOCs produced by ES-120. Individual compounds showed limited activity, suggesting that growth promotion may depend on interactions among multiple VOCs or on an undetected low-abundance compound. In greenhouse trials, ES-120 reduced wilt in tomato (Solanum lycopersicum) and increased the biomass of Chinese cabbage (Brassica rapa var. chinensis). Thus, B. velezensis ES-120 functions as a dual-purpose bioinoculant: its soluble metabolites suppress soil-borne pathogens and its VOCs enhance plant growth via auxin and BR pathways, highlighting its potential for sustainable agriculture.
Yang et al. (Sun,) studied this question.