The Plant-Beneficial Rhizobacterium Bacillus velezensis FZB42 Controls the Soybean Pathogen Phytophthora sojae Due to Bacilysin Production

Abstract

Soybean root rot caused by the oomycete Phytophthora sojae is a serious soil-borne disease threatening soybean production in China. Bacillus velezensis FZB42 is a model strain for Gram-positive plant growth-promoting rhizobacteria and is able to produce multiple antibiotics. In this study, we demonstrated that B. velezensis FZB42 can efficiently antagonize P. sojae. The underlying mechanism for the inhibition was then investigated. The FZB42 mutants deficient in the synthesis of lipopeptides (bacillomycin D and fengycin), known for antifungal activities, and polyketides (bacillaene, difficidin, and macrolactin), known for antibacterial activities, were not impaired in their antagonism toward P. sojae ; in contrast, mutants deficient in bacilysin biosynthesis completely lost their antagonistic activities toward P. sojae , indicating that bacilysin was responsible for the activity. Isolated pure bacilysin confirmed this inference. Bacilysin was previously shown to be antagonistic mainly toward prokaryotic bacteria rather than eukaryotes. Here, we found that bacilysin could severely damage the hyphal structures of P. sojae and lead to the loss of their intracellular contents. A device was invented allowing interactions between P. sojae and B. velezensis FZB42 on nutrient agar. In this manner, the effect of FZB42 on P. sojae was studied by transcriptomics. FZB42 significantly inhibited the expression of P. sojae genes related to growth, macromolecule biosynthesis, pathogenicity, and ribosomes. Among them, the genes for pectate lyase were the most significantly downregulated. Additionally, we showed that bacilysin effectively prevents soybean sprouts from being infected by P. sojae and could antagonize diverse Phytophthora species, such as P. palmivora , P. melonis , P. capsici , P. litchi , and, most importantly, P. infestans . Importance Phytophthora spp. are widespread eukaryotic phytopathogens and often extremely harmful. Phytophthora can infect many types of plants important to agriculture and forestry and thus cause large economic losses. Perhaps due to inappropriate recognition of Phytophthora as a common pathogen in history, research on the biological control of Phytophthora is limited. This study shows that B. velezensis FZB42 can antagonize various Phytophthora species and prevent the infection of soybean seedlings by P. sojae . The antibiotic produced by FZB42, bacilysin, which was previously known to have antibacterial effectiveness, is responsible for the inhibitory action against Phytophthora . We further showed that some Phytophthora genes and pathways may be targeted in future biocontrol studies. Therefore, our data provide a basis for the development of new tools for the prevention and control of root and stem rot in soybean and other plant diseases caused by Phytophthora .

Bacillus velezensis SYL-3 suppresses Alternaria alternata and tobacco mosaic virus infecting Nicotiana tabacum by regulating the phyllosphere microbial community

“…Previous investigations reported that B. velezensis produced a variety of metabolites, regulating the microbial community structure, and can effectively inhibit a variety of crop diseases. For instance, B. velezensis FZB42 eff iciently antagonizes Phytophthora sojae by producing bacilysin ( Han et al, 2021 ). B. velezensis B-4 is effective in controlling Sclerotinia sclerotiorum by synthesizing non-ribosomal peptide synthetases, polyketide synthases, and lantipeptide synthesis proteins ( Zhu et al, 2020 ).…”

Effects of Volatile Organic Compounds Produced by Pseudomonas aurantiaca ST-TJ4 against Verticillium dahliae

“…Three seedlings were assayed for each treatment. The assays were performed third to determine their reproducibility [ 28 ].…”

2 E ,4 E -Decadienoic Acid, a Novel Anti-Oomycete Agent from Coculture of Bacillus subtilis and Trichoderma asperellum

“…SEM and TEM were implemented according to previously detailed methods ( 59 – 61 ). The DDA treatment method was the same as that described above to obtain media with final concentrations of 35 (EC 50 ) and 70 (2× EC 50 ) μg/mL.…”