Biocontrol potential of Bacillus subtilis CTXW 7-6-2 against kiwifruit soft rot pathogens revealed by whole-genome sequencing and biochemical characterisation

Abstract

Soft rot causes significant economic losses in the kiwifruit industry. This study isolated strain CTXW 7-6-2 from healthy kiwifruit tissue; this was a gram-positive bacterium that produced the red pigment pulcherrimin. The phylogenetic tree based on 16S ribosomal RNA, gyrA, rpoB, and purH gene sequences identified CTXW 7-6-2 as a strain of Bacillus subtilis. CTXW 7-6-2 inhibited hyphal growth of pathogenic fungi that cause kiwifruit soft rot, namely, Botryosphaeria dothidea, Phomopsis sp., and Alternaria alternata, by 81.76, 69.80, and 32.03%, respectively. CTXW 7-6-2 caused the hyphal surface to become swollen and deformed. Volatile compounds (VOC) produced by the strain inhibited the growth of A. alternata and Phomopsis sp. by 65.74 and 54.78%, respectively. Whole-genome sequencing revealed that CTXW 7-6-2 possessed a single circular chromosome of 4,221,676 bp that contained 4,428 protein-coding genes, with a guanine and cytosine (GC) content of 43.41%. Gene functions were annotated using the National Center for Biotechnology Information (NCBI) non-redundant protein, Swiss-Prot, Kyoto Encyclopedia of Genes and Genomes, Clusters of Orthologous Groups of proteins, Gene Ontology, Pathogen–Host Interactions, Carbohydrate-Active enZYmes, and Rapid Annotations using Subsystem Technology databases, revealing non-ribosomal pathways associated with antifungal mechanisms, biofilm formation, chemotactic motility, VOC 3-hydroxy-2-butanone, cell wall-associated enzymes, and synthesis of various secondary metabolites. antiSMASH analysis predicted that CTXW 7-6-2 can produce the active substances bacillaene, bacillibactin, subtilosin A, bacilysin, and luminmide and has four gene clusters of unknown function. Quantitative real-time PCR (qRT-PCR) analysis verified that yvmC and cypX, key genes involved in the production of pulcherrimin, were highly expressed in CTXW 7-6-2. This study elucidates the mechanism by which B. subtilis strain CTXW 7-6-2 inhibits pathogenic fungi that cause kiwifruit soft rot, suggesting the benefit of further studying its antifungal active substances.

Biocontrol and Growth Promotion Potential of Bacillus subtilis CTXW 7-6-2 against Rhizoctonia solani that Causes Tobacco Target Spot Disease

“…The colony diameter of R. solani after treatment with CTXW 7-6-2 was 0.43 ± 0.03 cm, and the inhibition rate was 94.02 ± 0.41%. The results are similar to those of a study by Chen et al (2022) .…”

“…The biocontrol strain and pathogenic fungi were preserved at the Kiwifruit Engineering Technology Research Center of Guizhou University, stored in glycerol at −80°C. The isolation method and in vitro antifungal activity assay, as described by Chen et al (2022) , were employed in the study. The cell concentration of the CTXW 7-6-2 culture medium was adjusted to 1 × 10 7 CFU/ml before application.…”

“…An antifungal area on the edge of the hyphae was selected to evaluate the restraining effect of CTXW 7-6-2. Hyphal morphology and cell ultrastructure were observed using the SU8100 scanning electron microscope (SEM) (Hitachi, Japan) and JEM1200EX transmission electron microscope (TEM) ( Mo et al 2021 ; Chen et al 2022 ).…”

Biocontrol of almond canker diseases caused by Botryosphaeriaceae fungi

“…15 In addition, several bacterial strains from the genus Bacillus, Streptomyces, Pseudomonas and Xenorhabdus have demonstrated, alone or in combination with other BCAs, their antagonism against Botryosphaeriaceae species in several crops. 38,40,[44][45][46][47][48][49][50][51][52] Rhizospheric bacteria have been demonstrated as potential biocontrol agents of the soil-borne pathogen M. phaseolina within the Botryosphaeriaceae family in strawberry crops. 53,54 However, to the best of our knowledge, no control agents based on bacterial strains have been successfully tested against canker diseases caused by Botryosphaeriaceae in almond.…”

“…atroviride SC1 has been registered in California as a biological control agent against almond canker pathogens 15 . In addition, several bacterial strains from the genus Bacillus , Streptomyces , Pseudomonas and Xenorhabdus have demonstrated, alone or in combination with other BCAs, their antagonism against Botryosphaeriaceae species in several crops 38,40,44–52 . Rhizospheric bacteria have been demonstrated as potential biocontrol agents of the soil‐borne pathogen M .…”