Bacillus thuringiensis and Bacillus weihenstephanensis Inhibit the Growth of Phytopathogenic Verticillium Species

Abstract

Verticillium wilt causes severe yield losses in a broad range of economically important crops worldwide. As many soil fumigants have a severe environmental impact, new biocontrol strategies are needed. Members of the genus Bacillus are known as plant growth-promoting bacteria (PGPB) as well as biocontrol agents of pests and diseases. In this study, we isolated 267 Bacillus strains from root-associated soil of field-grown tomato plants. We evaluated the antifungal potential of 20 phenotypically diverse strains according to their antagonistic activity against the two phytopathogenic fungi Verticillium dahliae and Verticillium longisporum. In addition, the 20 strains were sequenced and phylogenetically characterized by multi-locus sequence typing (MLST) resulting in 7 different Bacillus thuringiensis and 13 Bacillus weihenstephanensis strains. All B. thuringiensis isolates inhibited in vitro the tomato pathogen V. dahliae JR2, but had only low efficacy against the tomato-foreign pathogen V. longisporum 43. All B. weihenstephanensis isolates exhibited no fungicidal activity whereas three B. weihenstephanensis isolates showed antagonistic effects on both phytopathogens. These strains had a rhizoid colony morphology, which has not been described for B. weihenstephanensis strains previously. Genome analysis of all isolates revealed putative genes encoding fungicidal substances and resulted in identification of 304 secondary metabolite gene clusters including 101 non-ribosomal polypeptide synthetases and 203 ribosomal-synthesized and post-translationally modified peptides. All genomes encoded genes for the synthesis of the antifungal siderophore bacillibactin. In the genome of one B. thuringiensis strain, a gene cluster for zwittermicin A was detected. Isolates which either exhibited an inhibitory or an interfering effect on the growth of the phytopathogens carried one or two genes encoding putative mycolitic chitinases, which might contribute to antifungal activities. This indicates that chitinases contribute to antifungal activities. The present study identified B. thuringiensis isolates from tomato roots which exhibited in vitro antifungal activity against Verticillium species.

Response of Soil Bacterial Community and Pepper Plant Growth to Application of Bacillus thuringiensis KNU-07

“…In this study, we assessed the effect of KNU-07 on the growth of pepper plants and the soil bacterial community and designed a strain-specific primer pair to track the population dynamics of KNU-07 in soil using a qPCR-based method. Similar to the results of our in vitro assays, IAA production, siderophore production, phosphate solubilization, and urease activity by several strains of B. thuringiensis have been previously reported [12][13][14]. An increase in IAA production in the presence of L-tryptophan may attributed to the nature of the strain to utilize L-tryptophan as a physiological precursor [35].…”

“…In addition, although the effect of PGPR on the indigenous soil bacterial communities and their functional properties has been studied, there is very limited information on the effects of B. thuringiensis on bacterial communities in the soil [10,11]. The beneficial effects of B. thuringiensis on plants are due to direct and indirect mechanisms, including nitrogen fixation, siderophore production, plant nutrient solubilization, and plant growth hormone production [12][13][14]. However, the plant responses are often variable due to inconsistent performance of inoculants under field conditions [15].…”

Chitinases of Bacillus thuringiensis: Phylogeny, Modular Structure, and Applied Potentials

“…Isolates of B. thuringiensis have shown antifungal potential in dual cultivation assays. For example, Hollensteiner et al (2017) showed in vitro antagonism toward Verticillium dahlia, a pathogen with a broad host range, including economically important crops such as tomato. The authors suggested that the inhibitory effect on the growth of the phytopathogens was attributed to the presence of chitinases in the supernatant of the bacterial culture.…”

“…Biological structures made of chitin are prime targets for chitinolytic enzymes, and as such, phytopathogenic fungi or pest insects are susceptible to degradation by chitinases (Morales de la Vega et al, 2006;Juárez-Hernández et al, 2015;Hollensteiner et al, 2017). Chitinases are produced and secreted by viruses, prokaryotes, and eukaryotes, including humans, plants, fungi, and insects, which interestingly may or not have chitin.…”

Mining, Isolation and Identification of Siderophore Synthesis Gene from Brevibacillus brevis GZDF3

“…Bacillus anthracis and Bacillus cereus can not only synthesize Bacillibactin, but also synthesize Petrobactin. The complete Bacillibactin and Petrobactin synthesis gene cluster have been found in the genome of Bacillus thuringiensis (Wilson et al, 2006;Hollensteiner et al, 2016). Bacterial siderophore is not only a wide variety of species, but also a variety of functions.…”