Abstract
The endophytic bacterial strain Hil4 was isolated from leaves of the medicinal plant Hypericum hircinum. It exhibited antifungal activity against Botrytis cinerea and a plethora of plant growth promoting traits in vitro. Whole genome sequencing revealed that it belongs to Bacillus halotolerans and possesses numerous secondary metabolite biosynthetic gene clusters and genes involved in plant growth promotion, colonization, and plant defense elicitation. The Mojavensin cluster was present in the genome, making this strain novel among plant-associated B. halotolerans strains. Extracts of secreted agar-diffusible compounds from single culture secretome extracts and dual cultures with B. cinerea were bioactive and had the same antifungal pattern on TLC plates after bioautography. UHPLC-HRMS analysis of the single culture secretome extract putatively annotated the consecutively produced antimicrobial substances and ISR elicitors. The isolate also proved efficient in minimizing the severity of gray mold post-harvest disease on table grape berries, as well as cherry tomatoes. Finally, it positively influenced the growth of Arabidopsis thaliana Col-0 and Solanum lycopersicum var. Chondrokatsari Messinias after seed biopriming in vitro. Overall, these results indicate that the B. halotolerans strain Hil4 is a promising novel plant growth promoting and biocontrol agent, and can be used in future research for the development of biostimulants and/or biological control agents.
Highlights
Analysis showing thetic gene clusters (BGC) of secondary metabolites and their flanking genes, along with one of the best hits in ClusterBlast gene clusters (BGC) of secondary metabolites and their flanking genes, along with one of the best hits in ClusterBlast and and the closest core biosynthetic gene clusters of known BGC listed in the MIBiG database
Our studies provided the first example that clustered genes such as mojavensin BGC are jointly transferred in B. halotolerans species and inserted in specific regions that may represent hot spots for BGC acquisition
The results of the present multidisciplinary study suggest that the endophytic bacterial strain B. halotolerans Hil4 represents a promising agent for agricultural use
Summary
The adverse effects of the overuse of chemical pesticides and fertilizers on the environment and human health have created the need for alternative environmentally friendly strategies to minimize chemical inputs in agricultural practices, such as the use of beneficial plant-associated microorganisms called plant growth promoting microorganisms (PGPM). They can enhance plant growth characteristics, mitigate abiotic plant stress, and/or protect plants from phytopathogenic microbes and pests, acting as biostimulants and/or biological control agents (BCAs) [2,3]. PGPM can solubilize nutrients, produce plant growth regulators and antagonize plant pathogens through the production of antimicrobial metabolites, the induction of plant defense, and space competition [2,3].
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