Endophytic Strain Bacillus subtilis 26DCryChS Producing Cry1Ia Toxin from Bacillus thuringiensis Promotes Multifaceted Potato Defense against Phytophthora infestans (Mont.) de Bary and Pest Leptinotarsa decemlineata Say

Abstract

Novel properties of a previously obtained Bacillus subtilis 26DCryChS strain are described. The B. subtilis 26DCryChS strain is able to produce Cry1Ia δ-endotoxin from B. thuringiensis B-5351 and to exist in internal plant tissues of potato plants in the same manner as the endophytic B. subtilis 26D source strain (487 ± 53 and 420 ± 63 CFU*103/g, respectively). B. subtilis 26DCryChS, as much as the original B. subtilis 26D strain, inhibited mycelium growth of oomycete Phytophthora infestans (Mont.) de Bary and reduced late blight symptoms development on plants by 35% compared with non-treated ones, as well as showed insecticidal activity against Leptinotarsa decemlineata. Production of the fluorescent GFP protein in the B. subtilis 26D genome allowed visualizing the endophytes around damaged sites on beetle intestines. Bacillus strains under investigation induced systemic resistance to P. infestans and L. decemlineata through the activation of the transcription of PR genes in potato plants. Thus, the B. subtilis 26DCryChS strain was able to induce transcription of jasmonate-dependent genes and acquired the ability to promote transcription of a salicylate-dependent gene (PR1) in plants infected with the late blight agent and damaged by Colorado potato beetle larvae. The B. subtilis 26DCryChS strain could be put forward as a modern approach for biocontrol agents design.

Endophytic Strain Bacillus subtilis 26D Increases Levels of Phytohormones and Repairs Growth of Potato Plants after Colorado Potato Beetle Damage

“…Arabidopsis mutant aba2-1 with a low ABA level demonstrated low expression of the marker of MYC-pathway gene VSP2 and high expression of the marker gene of ERF-pathway PDF1.2 within 30 h after injury caused by caterpillars Pieris rapae [ 35 ]. Indeed, in our previous work, the mortality of CPB larvae that were directly treated by suspension of B. subtilis 26D bacteria exceeded the control values by no more than 15%, while CPB larvae that ate plants containing the endophytic B. subtilis 26D strain exceeded these values by no more than 35% at the same time point after exposure [ 16 ], which indicated the effectiveness of induced plant defense reactions.…”

“…Previously, data on the alterations of plant growth by bacteria of the genus Bacillus under the influence of biotic and abiotic factors were summarized in the reviews [ 15 , 17 ]. However, investigations of the effect of PGPM on productivity of plants that were damaged by insect pests emphasize the direct insecticidal effect of strains under study [ 18 ] or their ability to induce plant resistance [ 16 ], but not their effect on the growth of damaged plants.…”

“…System “Plant + endophyte”: 14-day-old plants were inoculated with 5 μL of B. subtilis 26D suspension on the stem neighbor of the zone of formation of adventitious roots according to the previously described method [ 16 ]. Concentration of bacterial cells was 10 8 cells/mL.…”

“…In order to damage plants treated with water or B. subtilis 26D suspension, adult CPBs were placed in test tubes with cultivated plants for 3–5 min, one at a time [ 16 ]. During this time, one adult ate about 2–3 mg of leaves of one plant, after which the insect was removed.…”

“…Thus, consuming plants containing B. subtilis 26D by CPBs resulted in 38.1% larvae death. The presence of endophytic B. subtilis 26D strain cells in potato plants enhanced the level of transcripts of jasmonate-biosynthesis genes in plant leaves damaged by L. decemlineata [ 16 ] and decreased the population density of CPBs under the field conditions [ 15 ]. In this context, the question about the influence of B. subtilis 26D on growth parameters of potato plants is very important.…”