Relevance of multi-target action in the biocontrol mechanisms of Enterobacter pseudoroggenkampii GVv1 against Phytophthora sojae

We previously reported that the rhizobacterium Enterobacter pseudoroggenkampii strain GVv1 protects soybeans against Phytophthora root and stem rot (PRSR), caused by Phytophthora sojae . In this study, we explored GVv1’s mode of action by comparing its effects on P. sojae with three bacterial strains showing low or no protective activity against PRSR. All strains inhibited hyphal growth, but only GVv1 disrupted multiple infection stages. Exposure to GVv1 cell suspensions or volatiles reduced zoosporangium formation by about 97% and 92%, respectively. GVv1 also decreased zoospore migration toward soybean roots by 66%. Capillary chemotaxis assays revealed that GVv1 significantly reduced zoospore migration toward root exudates, 10 μM daidzein, and 10 μM genistein by 88%, 49%, and 58%, respectively. GVv1 culture filtrates also suppressed zoospore migration toward daidzein and inhibited zoospore germination. In contrast, split-root assays showed that GVv1 did not induce systemic resistance in soybean against PRSR. Genome analysis identified several biocontrol-related genes such as hydrolytic enzymes, lipopeptides, volatiles, phenazine derivatives, toxoflavin, bacilysin, as well as six secondary metabolite biosynthetic gene clusters, including a hybrid NRPS-T1PKS, terpene precursor, azole-containing RiPP, and siderophore biosynthetic genes. Overall, experimental results along with genomic evidence indicate that GVv1 exerts biocontrol primarily through direct inhibition of various P. sojae infection behaviors, likely mediated by diffusible and volatile inhibitory compounds. • Biocontrol by E. pseudoroggenkampii GVv1 against PRSR was investigated. • GVv1 disrupted multiple infection stages, unlike low protective strains. • GVv1 acts via diffusible and volatile compounds, not by inducing plant resistance. • Genome analysis found multiple antifungal compounds in GVv1.