Isolation and Characterization of Bacillus velezensis EB14, an Endophytic Bacterial Strain Antagonistic to Poplar Stem Canker Pathogen Sphaerulina musiva and Its Interactions with the Endophytic Fungal Microbiome in Poplar

Abstract

Species of the genus Populus commonly known as poplars are one of the most widely used groups of forest trees in North America and Europe, and play a significant ecological role as a pioneer species in boreal forests, and as a dominant species in the riparian forests that serve as wildlife habitats and watersheds. Natural and artificial hybrids of poplars are being extensively used in commercial plantations. However, many hybrid poplar trees are susceptible to Sphaerulina musiva, the pathogenic fungus that causes leaf spots and stem cankers and limits the utility of hybrid poplars as a plantation trees. We isolated an endophytic bacterial strain Bacillus velezensis EB14 from a Populus hybrid which showed a strong antifungal activity against S. musiva. Through mass spectrometric analyses of co-cultured B. velezensis EB14 and S. musiva, we identified five cyclic lipopeptides produced by B. velezensis EB14 – Iturin A1, Iturin A2, Iturin A9, Subtulene A and Fengycin. In addition, B. velezensis EB14 produced four major unidentified compounds in co-cultivation with S. musiva. The cyclopeptide production by B. velezensis EB14 was more pronounced (20-1000 fold) in the co-cultured plates due to elicitation by S. musiva. We also discovered that the native endophytic B. velezensis EB14 strain exhibited different levels of interactions against the endophytic fungal microbiomes of Populus sp. Overall, our results indicate B. velezensis EB14 strain as a promising biocontrol agent that could be used against stem canker and leaf spot diseases caused by S. musiva in Poplar plantations.

Foliar endophyte diversity in Eastern Asian-Eastern North American disjunct tree species – influences of host identity, environment, phylogeny, and geographic isolation

“…However, we detected multiple endophyte taxa (mainly from Ascomycota and Basidiomycota) associated with host phylogenies in both disjunct species and within Cornus ( Table 3 ). For instance, the beta diversity of species of the fungus Sphaerulina (Mycosphaerellaceae) (some of which are known fungal pathogens causing leaf spot and stem cankers - e.g., in poplar, Naik et al., 2021 ) are significantly correlated (Spearman’s rank in the Mantel test) with the phylogenetic distance among Cornus hosts (r = 0.6, Table 3 ). It would be interesting to evaluate the roles of Sphaerulina in the ecology (such as disease resistance), diversification, and evolution of Cornus .…”

Editing Metabolism, Sex, and Microbiome: How Can We Help Poplar Resist Pathogens?

“…For example, B. velezensis strain EB14, according to mass spectrometric analysis data, produces five cyclic lipopeptides: iturins A1, A2 and A9, as well as subtulene A and fengycin, thereby inhibiting the growth of S. musiva. Clusters of antibiotic biosynthesis of surfactin, rhizoactin, difficidin, macrolactin, and bacilysin were detected in its genome, and the possibility of the biosynthesis of subtulene and fengycin was also confirmed [273,274]. Also, Streptomyces sp.…”

The Imperative Use of Bacillus Consortium and Quercetin Contributes to Suppress Fusarium Wilt Disease by Direct Antagonism and Induced Resistance

“…All plates were then kept at 28 • C for 5 days. Bacteria were characterized into three categories e.g., bacteria showing zone of growth inhibition; bacteria showing contact inhibition; bacteria showing no Inhibition [28]. The bacteria showing a clear zone of growth inhibition were selected for further studies.…”