Rhizospheric Bacillus amyloliquefaciens Protects Capsicum annuum cv. Geumsugangsan From Multiple Abiotic Stresses via Multifarious Plant Growth-Promoting Attributes

Plant growth-promoting rhizobacteria (PGPR) are beneficial microorganisms that can be utilized to improve plant responses against biotic and abiotic stresses. In this study, we investigated whether PGPR (Bacillus amyloliquefaciens) isolated from the endorhizosphere of Sasamorpha borealis have the potential to sustain pepper growth under drought, salinity, and heavy metal stresses. The bacterial strain was determined based on 16S rDNA and gyrB gene sequencing and characterized based on the following biochemical traits: nitrogen fixation; 1-aminocyclopropane-1-carboxylate deaminase activity; indole acetic acid production; inorganic phosphate, potassium, zinc, and silicon solubilization; and siderophore production. Various abiotic stresses were applied to 28-day-old pepper seedlings, and the influence of the PGPR strain on pepper seedling growth under these stress conditions was evaluated. The application of PGPR improved survival of the inoculated pepper plants under stress conditions, which was reflected by higher seedling growth rate and improved physiochemical traits. The PGPR-treated plants maintained high chlorophyll, salicylic acid, sugar, amino acid, and proline contents and showed low lipid metabolism, abscisic acid, protein, hydrogen peroxide contents, and antioxidant activities under stress conditions. Gene expression studies confirmed our physiological and biochemical findings. PGPR inoculation led to enhanced expression of XTH genes and reduced expression of WRKY2, BI-1, PTI1, and binding immunoglobulin protein (BiP) genes. We conclude that the PGPR strain described in this study has great potential for use in the phytoremediation of heavy metals and for enhancing pepper plant productivity under stress conditions, particularly those involving salinity and drought.

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

Many Bacillus species are among the plant growth-promoting rhizobacteria (PGPR) that promote the growth of many different plant species. This study aimed to investigate the effects of Bacillus thuringiensis KNU-07 on the growth of pepper plants and the soil microbiota. We also designed primers specific for the strain KNU-07 to monitor the population in pepper-cultivated soil. Accordingly, a strain-specific primer pair was designed using a database constructed from 16,160 complete bacterial genomes. We employed quantitative PCR (qPCR) to track the abundance of the strain KNU-07 introduced into pepper-cultivated soil using the strain-specific primers. Our study revealed that the strain was found to possess plant growth-promoting (PGP) activities, and it promoted the growth of pepper plants. The soil bacterial community structure due to the application of the PGPR strain was significantly changed after six weeks post-inoculation. In addition, based on qPCR analysis, the population of the introduced strain declined over time. In this study, application of a PGPR strain increased the growth of pepper plants and changed the soil bacterial community structure. The successful results of monitoring of a bacterial strain’s population using a single strain-specific primer pair can provide important information about the quantification of bio-inoculants under non-sterile soil conditions.

Bacillus subtilis CBR05 for Tomato (Solanum lycopersicum) Fruits in South Korea as a Novel Plant Probiotic Bacterium (PPB): Implications from Total Phenolics, Flavonoids, and Carotenoids Content for Fruit Quality

Plant growth-promoting rhizobacteria (PGPR) are naturally occurring soil biota which benefit plants by improving plant productivity and immunity. The aim of the present work was to evaluate the effect of the inoculation of PGPR strain, Bacillus subtilis CBR05 on the quality of tomato fruits produced under greenhouse conditions. Results were compared with mock-inoculated control and market sample. We found a significant increase in total phenol and flavonoid contents of tomato fruits in PGPR strain B. subtilis CBR05 inoculated plants compared to those of mock-inoculated control and market sample. Moreover, B. subtilis CBR05 inoculation stimulated antioxidant activities and levels of carotenoid (β carotene and lycopene) content in plants. In addition, the inoculation of the strain B. subtilis CBR05 produced the highest content of lycopene (21.08 μg/g FW) in tomato fruits as compared to mock-inoculated plants. Our results show that the PGPR strain B. subtilis CBR05 is a versatile soil bacterium that enhances tomato production by elevating antioxidant activities and carotenoid (β carotene and lycopene) levels in fruit.

Biocontrol of PGPR strain Bacillus amyloliquefaciens Ba168 against Phytophthora nicotianae on tobacco

Tobacco black shank (TBS) caused by Phytophthora nicotianae is destructive to almost all kinds of tobacco cultivars and is widespread in many tobacco-planted countries. Here, an isolated plant growth-promoting rhizobacteria (PGPR) strain Ba168 is promise in biocontrol of TBS. In vitro assays disclosed a strong P. nicotianae suppression activity and the field utilization potential (FUP) by characterized the crude extract of culture filtrates of Ba168. P. nicotianae’s growth was inhibited by the crude extract at minimum inhibitory concentration (MIC) of 5μl/mL. Extracellular conductivity, pH and the wet, dry weight of P. nicotianae’s mycelia, were significantly different after treated with different concentrations of the crude extract and the deformity and perforation of treated P. nicotianae’s hyphae can be observed in scanning electron microscope (SEM) analysis. Proteome characterizations of the crude extract were used as supplementary proofs that further evaluated FUP of Ba168. We then identified strain Ba168 as B. amyloliquefaciens by its genetic and phenotypic characteristics. Field assays comparatively evaluated TBS control efficacy of these PGPRs and agrochemicals. Pooling analysis of the results showed that the biocontrol efficacy of Ba168 preparation is only lower than Mixture of Propamocarb hydrochloride and Azoxystrobin (MPA) but better than other tested subjects. Although the existence of differences in biocontrol efficacy, PGPR preparations effectively reduced the disease index of tobacco.ImportanceThis work demonstrates the promising biocontrol potential of B. amyloliquefaciens Ba168 and highlights the positive roles of PGPR in suppression of this soil-borne disease.

PGPR-Induced Growth Stimulation and Nutrient Acquisition in Maize: Do Root Hairs Matter?

Here we describe the effects of the well-characterized, commercial plant growth-promoting rhizobacteria (PGPR) strain Pseudomonas sp. DSMZ 13134 (Proradix®) on plant growth, root morphology, and nutrient acquisition of a maize mutant (rth2) with impaired root hair production as compared with the corresponding wild type line, to study the importance of root hairs for the interaction of the PGPR strain with the host plant. The study was conducted in rhizobox culture with a sand–soil mixture and moderate P supply. Root hair development of the mutant was clearly impaired, reflected by slower growth and limited elongation as compared with the wild type line. This defect was compensated by more intense root growth and fine root production of the mutant which was particularly expressed after inoculation with Proradix®. By contrast, PGPR inoculation had no effect on root hair length. The beneficial effects of Proradix® on root growth were reflected in higher shoot contents of the macronutrients P and K. Interestingly, negative effects on shoot accumulation of the micronutrients Zn and Cu were observed. These findings support proposed PGPR effects of this strain but also show limitations that may be explained by additional strain-specific properties. Possible implications of these findings are discussed.