Biocontrol and Action Mechanism of Bacillus subtilis Lipopeptides’ Fengycins Against Alternaria solani in Potato as Assessed by a Transcriptome Analysis

Abstract

Alternaria solani is an airborne fungus and the primary causal agent of potato early blight worldwide. No available fungicides that are both effective and environmentally friendly are usable to control this fungus. Therefore, biological control is a potential approach for its suppression. In this study, Bacillus subtilis strain ZD01’s fermentation broth strongly reduced A. solani pathogenicity under greenhouse conditions. The effects of strain ZD01’s secondary metabolites on A. solani were investigated. The exposure of A. solani hyphae to the supernatant resulted in swelling and swollen sacs, and the ZD01 supernatant reduced A. solani conidial germination significantly. Matrix-assisted laser desorption/ionization time of flight mass spectrometry and pure product tests revealed that fengycins were the main antifungal lipopeptide substances. To elucidate the molecular mechanism of the fengycins’ biological control, RNA sequencing analyses were performed. A transcriptome analysis revealed that 304 and 522 genes in A. solani were differentially expressed after 2-h and 6-h fengycin treatments, respectively. These genes were respectively mapped to 53 and 57 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. In addition, the most enriched KEGG pathway analysis indicated that the inhibitory mechanisms of fengycins against A. solani regulated the expression of genes related to cell wall, cell membrane, transport, energy process, protein synthesis and genetic information. In particular, cell wall and cell membrane metabolism were the main processes affected by fengycin stress. Scanning and transmission electron microscope results revealed hyphal enlargement and a wide range of abnormalities in A. solani cells after exposure to fengycins. Furthermore, fengycins induced chitin synthesis in treated cells, and also caused the capture of cellular fluorescent green labeling and the release of adenosine triphosphate (ATP) from outer membranes of A. solani cells, which may enhance the fengycins ability to alter cell membrane permeability. Thus, this study increases the transcriptome data resources available and supplies a molecular framework for B. subtilis ZD01 inhibition of A. solani HWC-168 through various mechanisms, especially damaging A. solani cell walls and membranes. The transcriptomic insights may lead to an effective control strategy for potato early blight.

Antifungal Lipopeptide Production and Tomato Early Blight Control by Bacillus velezensis B157

“…These results suggest a protective effect of the antifungal LPs produced by B157 on tomato leaves, suppressing conidial germination, germ tube elongation and/or penetration. The effects of LPs from different Bacillus strains on Alternaria solani and A. alternata reported in the literature include the induction of germ tube and hyphal deformities, disruption of cellular membrane integrity and inhibition of conidial germination (Zhang et al 2021(Zhang et al , 2022Ali et al 2016). Treatment with the organic extract of B157 at 2,5 mg/mL completely inhibits conidial germination of A. linariarie AS248P (data not shown).…”

Evaluation of the Biocontrol Efficiency of Bacillus subtilis Wettable Powder on Pepper Root Rot Caused by Fusarium solani

“…Bais et al [ 8 ] demonstrated that Surfactin absence resulted in the decrease of biofilm formation and thereby reduced its ability to colonize the roots, which led to a decrease in the control effect of Pseudomonas syringae . Fengycin, secreted by B. subtilis ZD01, effectively limited the development of the lesion area of potato early blight and caused mycelial and conidial malformations [ 28 ]. Zhao et al [ 29 ] showed that fengycin impacted the cell membrane of F. graminearum and led to the release of cell contents.…”

Inhibitory roles of Bacillus velezensis YE-1 isolated from lichens in Baiyin city, Gansu province against Aspergillus flavus

“…In many cases, the inhibitory effect of Bacillus on fungi is attributed to non-protein active substances. For example, Jiao et al and Zhang et al [48,49] have con rmed that the main inhibitory substances of Bacillus amyloliquefaciens/subtilis were lipopeptides. Moreover, lipopeptides synthesized through non-ribosomal pathways have the advantages of safety,…”