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Tomato is attributed as a global host for root-knot nematode (Meloidogyne incognita) soliciting ponderous damage. Using biocontrol agents to control plant parasitic nematodes is a well-established, green approach in advance of synthetic nematicides. The role of Bacillus spp. in inciting physiological and biochemical alterations in nematode infestation is discussed in the present study. The susceptible (PKM-1) and resistant (Hisar Lalit) tomato cultivars treated with Bacillus pumilus augmented the shoot length, root length and biomass of plants compared to the standard check, Pseudomonas fluorescens, followed by B. megaterium. Accordingly, all the biocontrol agent-treated susceptible plants showed reduced galling and exhibited a root gall index of 3 (moderately resistant). Contrarily, all the resistant plants showed highly resistant reactions. B. pumilus showed the topmost expression of all the biochemical enzymes like peroxidase (PO), polyphenol oxidase (PPO), catalase (CAT), phenylalanine ammonia-lyase (PAL) and total phenols. Conclusively, B. pumilus was found to be the most potential in reducing nematode infestation by embellishing the plant growth and enhancing defense-related enzymes in tomatoes.

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Surfactin is one of the most efficient biosurfactants excreted by Bacillus subtilis which displays the highest potential as induced systemic resistance elicitor among all metabolites produced by B. subtilis. Environmental factors have considerable effect on surfactin production. In this study surfactin production of two Bacillus subtilis strains were analyzed using high performance liquid chromatography (HPLC). C14 and C15 surfactins were detected in the ethanol extract from acid-precipitated supernatant. HPLC analyses of different media including Nutrient Broth (NB) medium, NB plus 40g/l glucose, NB plus 10% soil extract and NB plus 10% plant extract medium, clearly showed that these bacteria produced different amounts of surfactins C14 and C15 in these media. Surfactin production in NB/plant medium was relatively the highest in quantity. Microelements analysis of media containing plant and soil extract with atomic absorption spectrometry showed high amounts of Fe, Mn and Zn in medium containing plant extract compared with that of soil extract. Since these elements play an important role in surfactin production, high amounts of Fe, Mn and Zn in NB/plant extract medium compared to the NB/soil extract medium could be the possible reason for relatively higher amounts of surfactins C14 and C15 produced in NB/plant medium. So adding these important elements to soil may boost biocontrol effect of B. subtilis against plant pathogens.

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Fluorescence-activated cell sorting (FACS) as a novel and sensitive technology was used to evaluate the biocontrol efficiency of Bacillus subtilis against Agrobacterium tumefaciens, a very destructive plant pathogen. The combination of two methods of culturing and cell sorting by FACS technology was used to distinguish a rapid and accurate method in monitoring the biocontrol effect of Bacillus (ATCC21332) on Agrobacterium (IBRC-M10701 and AGL1),. The culture method indicated that the B. subtilis could suppress A. tumefaciens in vitro and in vivo. We used a green fluorescent protein (GFP), reporter, to flow cytometric analysis using FACS. The mean of GFP expression levels was significantly reduced to 17.98, 16.48, and 11.27% in treatments 24, 48, and 72 h post-treatment; however, it was 31.57, 26.06, and 23.98% in the nontreated ones. The experiments demonstrated a positive biocontrol effect of Bacillus against Agrobacterium. Overall, our findings may provide a basis for improving the new rapid biocontrol agent detection method based on FACS.
 

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Throughout the present study, some Bacillus spp. were isolated from soil, and the effectiveness of the medicinal plant Cuminum cyminum L.’s essential oil extracts were tested against the isolated bacteria. The Bacillus spp.were identified through 16S rDNA sequence analysis and the antibacterial activity of various organic solvent extracts as well as the essential oils of C. cyminum L. determined in vitro using agar diffusion method and Minimal Inhibitory Concentration (MIC) tests. The hydrodistilled essential oil was analyzed through GC-MS. Twenty-seven compounds representing 92.61% of the total oil were identified. Oxygenated monoterpenes and scsquiterpene hydrocarbons constituted the major components of the oil. The inhibition zones of essential oil (extracted through organic solvent) against the tested bacteria were found within the range of 14.4 to 20.2 mm. Organic extracts of C. cyminum L. also revealed a great potential of antibacterial activity against Bacillus spp. Among all the extracts, ethanol extract showed the highest activity against Bacillus megaterium with an inhibition zone of 22.9 mm and MIC value of 500 µg ml^-1. In most cases, the essential oil and organic extracts exhibited either similar or higher antibacterial activity in comparison with the standard drug Erythromycin. The results finally suggest that the essential oil as well as organic extracts of C. cyminum L. can act as sources of natural antimicrobial agents with potential applications in food and pharmaceutical industries.

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 In the present study, we aimed to screen indigenous rhizospheric Bacillus strains, capable of producing antiphytopathogenic and plant growth promoting traits. Isolate CTS-B19 and CTS-G24 exhibited quite noticeable antagonistic activity initially against Fusarium oxysporum f. sp. ciceri and Rhizoctonia bataticola, and, later, against a panel of phytopathogens. Partial 16S rRNA sequence analysis showed that the isolate CTS-B19 and CTS-G24 exhibited 99% homology with Paenibacillus polymyxa and Bacillus subtilis and the sequences were deposited in GenBank with accession numbers KF322038 and KF322037, respectively. In vitro detection for fungal wall degrading enzymes revealed that both isolates produced chitinases, β-1,3-glucanases, proteases and cellulases. While siderophores and catalase activities were observed only in Bacillus subtilis (CTS-G24), both strains exhibited a positive result for in vitro ammonia production. Besides, the strain CTS-B19 could also solubilize phosphate. Lytic enzymes and siderophore produced by Bacillus subtilis can be considered as potential antiphytopathogenic traits involved in the inhibition of fungal growth. Both strains exhibited either no or negligible antagonistic activity against other plant growth promoting bacteria. Additional to antagonism, plant growth promoting traits exhibited by these natural biocontrol agents may suppress plant diseases and might be applied in agriculture as an alternative to chemical pesticides and fertilizers.