Culex pipiens pallens are the most common mosquito's vector in Asia. In order to protect the people from diseases, the anti-mosquito population is necessary that uses safe and new bio-pesticides such as bacteria-AgNPs. In our report, we used two kinds of bacteria to synthesize silver nanoparticles to examine the toxic effect on the larvae and pupae of Cx. pipiens pallens and also used as antimicrobial activity. The biosynthesis of AgNPs and its characterization was carried out by UV-Vis spectrophotometry, FTIR, TEM, SEM, and EDX. The larvicidal and pupicidal assays revealed that the lethal concentration LC values of Bacillus amyloliquefaciens-AgNPs were 0.72 ppm (I), 0.73 ppm (II), 0.69 ppm (III), 1.16 ppm (IV), and 4.18 (Pupae), while LC values of Bacillus subtilis-AgNPs were 0.60 ppm (I), 0.62 ppm (II), 0.21 ppm (III), 0.28 ppm (IV), and 3.46 ppm (Pupae) after 72 h of exposure. Antibacterial activity test of AgNPs reveals better results against rice pathogenic bacteria than bacteria alone. Thus, bacteria-mediated silver nanoparticles have a rapid effect on vector mosquito and microbial pathogen suggesting savings of energy and resources. Hence, bacteria-AgNPs may be used in the future as an effective weapon to control vector mosquito and harmful bacteria.
Bacillus strains are broadly studied for their beneficial role in plant growth and biological control of plant disease and pest; however, little is known about their underlying mechanisms. In this study, we assessed the controlling and defence-related mechanisms of three Bacillus strains including rice seed-associated strain B. subtilis A15, rhizobacterial strains B. amyloliquefaciens D29 and B. methylotrophicus H8, all of which are against bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae. Results indicated that all three strains showed strong biofilm formation ability. The culture filtrates of each strain significantly suppressed the growth and biofilm formation of X. oryzae, while changes in bacterial cell morphology such as cell swell and severe cell wall alterations were observed through the transmission electron microscopy images. PCR analysis revealed that all three strains harbour the antimicrobial-associated genes that are responsible for biosynthesis of bacillomycin, fengycin, iturin and surfactin. Subsequent real-time qPCR analysis revealed the upregulated expression of fenD and srfAA genes in D29 and H8, and fenD and ituC genes in A15 during their in vitro interaction with X. oryzae. It suggests that the antibacterial mechanisms of the three strains may be at least partially associated with their ability to secrete corresponding lipopeptides. Interestingly, the applications of the three strains in greenhouse conditions were found to be effective in controlling the BLB disease, which was achieved through the activation of inducing systemic resistance resulted from the enhanced activities of defence-related enzymes. This is the first report of demonstration of the mode of antibacterial effect of Bacillus strains against X. oryzae. Overall, data from the current study provide valuable information for biological control of BLB disease in rice.
This study was conducted to assess efficacy of biological control against bacterial leaf blight of rice (BLB) produced by Xanthomonas oryzae pv. oryzae. Five endophytic strains (A1, A2, A3, A13, and A15) and two rhizospherial Bacilli (D29 and H8) were tested for their antagonistic activities against BLB in vitro and in vivo. All 7 strains showed high potential of antagonistic activity against X. oryzae pv. oryzae and three phytopathogenic fungi in vitro. Test of 16SrRNA Downloaded by [FU Berlin] at 00:39 04 July 2015A c c e p t e d M a n u s c r i p t Controlling Bacterial Leaf Blight of Rice with Bacillus strains 2 gene sequence were assigned isolates A1, A3 and A13 as Bacillus amyloliquefaciens while isolates A2 and A15 as Bacillus methylotrophicus and B. subtilis respectively. In greenhouse, 4 strains of displayed 50.29 % to 57.86 % inhibition rate against the pathogen and significantly increased plant fresh weight from 50.03 % to 73.11 % and dry weight from 64.11 % to 86.65 % in treated rice plants. In addition, these strains demonstrated strong capability to produce indole-3-acetic acid, siderophores, solubilizing phosphate and also colonize roots. Real-time qPCR revealed that expression of defense-related genes including OsAOS2, OsJMT1, OsNPR1, andOsPR1b were significantly up-regulated in leaves of D29-exposed rice plants suggesting that treatment of rice with D29 suppressed BLB through systemic activation of the plant defense system. Therefore, data suggest that Bacillus isolates A13, A15, D29 and H8 support effective antagonistic activity against BLB under greenhouse conditions in addition to their potential to promote growth of rice plants.
Honeybee (Apis mellifera) population is going down across the globe due to honeybee pathogens. This greatly influences the bee-associated commercial food products production. Likewise, mosquitoes are prominent vector responsible for spreading life-threatening human diseases, including malaria and dengue. The plant-based insecticides are a better substitute to the recent control practices of honeybee pathogenic bacteria and mosquito. Here, we performed in vitro screening of Nepeta clarkei Hook. f. (Labiatae) aqueous extracts against three honey bee gut bacterial isolates including Paenibacillus larvae an infamous honeybee bacterial pathogen. The inhibitory zone was produced in the range of 6-14 mm diameters against three honey bee bacterial isolates. Likewise, fourth instars larvae of Culex (Diptera/Culicidae) were also subjected to check the possible larvicidal efficacy of N. clarkei. A normal media supplemented with N. clarkei in different concentrations (0.025% 0.05%, 0.1%, 0.15%, and 0.2%) affected the growth of larvae significantly. The lethal concentration at which 50% of larvae failed to become pupate was found to be 0.1% after 24 h of exposure. Considerable reductions in larval growth and pupal development of mosquito suggested that this plant should be utilized in mosquito control programmes.
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