Characterization of a novel vip3-type gene from Bacillus thuringiensis and evidence of its presence on a large plasmid

A novel vip3-type gene named vip3LB has been isolated from Bacillus thuringiensis strain BUPM95. The corresponding secreted vegetative insecticidal protein was active against the lepidopteran insect Ephestia kuehniella. The vip3LB gene was shown, for the first time, to be carried by the large plasmid containing the cry1Ia genes of B. thuringiensis. The nucleotide sequence predicted a protein of 789 amino acids residues with a calculated molecular mass of 88.5kDa. Both nucleotide and amino acid sequences similarity analysis revealed that vip3LB is a new vip3-type gene, presenting several differences with the other vip3-type genes. Heterologous expression of the vip3LB under the control of the strong promoter P(BAD) was performed in Escherichia coli and the produced protein conferred insecticidal activity against Ephestia kuehniella. This novel vegetative insecticidal protein Vip3LB could be a very useful biological control agent.     

苏云金杆菌辅助蛋白P20对营养期杀虫蛋白Vip3A表达的影响

为检测苏云金杆菌辅助蛋白P20对Vip3A表达和杀虫活性的影响,将p20基因与vip3A基因相连构建了重组质粒pHVP20,然后电激转化至Bt中进行了共表达,以仅携带vip3A基因的质粒pHPT3作为对照质粒。Westernblot结果显示,当vip3A基因和p20基因在Bt无晶体缺陷株CryB中共表达时,Vip3A蛋白的最大表达量约是其在CryB(pHPT3)菌株中单独表达的1.5倍。生物测定结果表明,CryB(pHVP20)和CryB(pHPT3)菌株对初孵斜纹夜蛾幼虫的LC50值分别为48.79μg/mL和78.00μg/mL,这说明P20蛋白可以促进vip3A基因在Bt中的表达,但对提高Vip3A蛋白的杀虫毒力没有显著性帮助。     

<Emphasis Type="Italic">Prays oleae</Emphasis> Midgut Putative Receptor of <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> Vegetative Insecticidal Protein Vip3LB Differs from that of Cry1Ac Toxin

Vegetative insecticidal protein (Vip) is a class of insecticidal proteins produced by many Bacillus thuringiensis strains during their vegetative growth stage. The vip3LB gene of B. thuringiensis strain BUPM95, which encodes a protein active against the Lepidoptera olive tree pathogenic insect Prays oleae, was cloned into pET-14b vector and overexpressed in Escherichia coli. The expressed Vip3LB protein, found in the E. coli cytoplasmic fraction, was purified and used to produce anti-Vip3LB antibodies. Using the midgut extract of P. oleae, the purified Vip3LB bound to a 65-kDa protein, whereas Cry1Ac toxin bound to a 210-kDa midgut putative receptor. This result justifies the importance of the biological pest control agent Vip3LB that could be used as another alternative particularly in case of resistance to Cry toxins.     

Gene knockout demonstrates that vip3A contributes to the pathogenesis of Bacillus thuringiensis toward Agrotis ipsilon and Spodoptera exigua

Vip3A is an 89-kDa protein secreted by Bacillus thuringiensis during vegetative growth. To determine the importance of Vip3A for the insect pathogenicity of B. thuringiensis the vip3A gene was deleted from strain HD1, yielding strain HD1Deltavip3A. Compared with HD1, strain HD1Deltavip3A was one-fourth as toxic to Agrotis ipsilon larvae and less than one-tenth as toxic to Spodoptera exigua larvae. When streptomycin was included in the S. exigua diet the toxicity of HD1Deltavip3A was approximately half that of HD1. Addition of HD1 spores increased the toxicity of purified Cry1 protein more than 600-fold against S. exigua, whereas addition of HD1Deltavip3A spores increased toxicity of Cry1 protein approximately 10-fold. These results demonstrate that an important component of B. thuringiensis insecticidal activity against S. exigua is the synthesis of Vip3A protein by B. thuringiensis cells after ingestion of spores and crystal proteins by insect larvae.     

Heterologous Expression of Bacillus thuringiensis Vegetative Insecticidal Protein-Encoding Gene vip3LB in Photorhabdus temperata Strain K122 and Oral Toxicity against the Lepidoptera Ephestia kuehniella and Spodoptera littoralis

Photorhabdus temperata and Bacillus thuringiensis are entomopathogenic bacteria exhibiting toxicities against different insect larvae. Vegetative Insecticidal Protein Vip3LB is a Bacillus thuringiensis insecticidal protein secreted during the vegetative growth stage exhibiting lepidopteran specificity. In this study, we focused for the first time on the heterologous expression of vip3LB gene in Photorhabdus temperata strain K122. Firstly, Western blot analyses of whole cultures of recombinant Photorhabdus temperata showed that Vip3LB was produced and appeared lightly proteolysed. Cellular fractionation and proteinase K proteolysis showed that in vitro-cultured recombinant Photorhabdus temperata K122 accumulated Vip3LB in the cell and appeared not to secrete this protein. Oral toxicity of whole cultures of recombinant Photorhabdus temperata K122 strains was assayed on second-instar larvae of Ephestia kuehniella, a laboratory model insect, and the cutworm Spodoptera littoralis, one of the major pests of many important crop plants. Unlike the wild strain K122, which has no effect on the larval growth, the recombinant bacteria expressing vip3LB gene reduced or stopped the larval growth. These results demonstrate that the heterologous expression of Bacillus thuringiensis vegetative insecticidal protein-encoding gene vip3LB in Photorhabdus temperata could be considered as an excellent tool for improving Photorhabdus insecticidal activities.     

苏云金芽孢杆菌vip3A基因的检测及保守性分析

Vip3A蛋白是苏云金芽孢杆菌(Bacillus thuringiensis,Bt)在营养期分泌的一类新型杀虫蛋白。用PCR方法从114个Bl菌株和41个Bl标准菌株中筛选到39株即约25％的菌株含有vip3A基因。利用所制备的Vip3A蛋白的多克隆抗体对以上含有vip3A基因的Bt菌株进行Western印迹分析,发现多数PCR反应为阳性的菌株都产生89kD大小的蛋白,其中有4株没有Vip3A蛋白的表达。从以上菌株中挑选2个对夜蛾科害虫具有较高和较低毒力的菌株,即S101和6ll,并分别进行vip3A基因的克隆和测序,再与GenBank上所登录的其它6个全长vip3A基因和2个已报道的但未登录GenBank的vip3A基因进行核苷酸和氨基酸序列比较,结果表明,vip3A是一个极其保守的基因。将以上所克隆的2个却3A基因即vip3A—S101和vip3A-611分别插入表达载体pQE30构建了表达质粒pOTP-S101和pOTP-6ll,转化到大肠杆菌M15,经lmmol／L IPTG诱导后均表达89kD大小的Vip3A蛋白。蛋白可溶性试验表明,Vip3A-S101和Vip3A-611分别有48％和35％的蛋白是可溶的。将Vip3A-S101和Vip3A-6ll蛋白和已报道的Vip3A—S184蛋白对初孵斜纹夜蛾(Spodoptera litura)幼虫进行生物测定,结果表明,3个Vip3A蛋白对斜纹夜蛾幼虫毒力没有显著性差异,这说明了Vip3A个别氨基酸的变化对蛋白的杀虫活性没有影响。     

Expression of vip1/vip2 genes in Escherichia coli and Bacillus thuringiensis and the analysis of their signal peptides

AIMS: To determine the expression time courses and high expression level of Vip2A(c) and Vip1A(c) in Bacillus thuringiensis, and survey their insecticidal toxicity and insecticidal spectrum. METHODS AND RESULTS: A kind of new vegetative insecticidal toxin genes encoded by a single operon from B. thuringiensis had been cloned and sequenced. The individual genes, 5-terminus truncated genes and the operon were respectively expressed in Escherichia coli. Only N-terminus deleted Vip2A(c) and Vip1A(c) proteins could be purified by Ni-NTA agarose, while others were processed and their N-terminal signal peptides were cleaved. The individual genes and the operon were also expressed in B. thuringiensis. Both proteins were mostly secreted into the cell supernatants. The expression level of Vip1A(c) was influenced because of the interruption of vip2A(c) gene on the operon. Bioassays showed that neither separate protein nor both performed any toxicity against tested lepidopteran and coleopteran insects. CONCLUSIONS: Vip2A(c) and Vip1A(c) have similar secretion mechanism in E. coli and B. thuringiensis. Vip1A(c) remained its high expression level only when being expressed with vip2A(c) gene as an operon in B. thuringiensis. SIGNIFICANCE AND IMPACT OF THE STUDY: Expression of vip2A(c) and vip1A(c) genes in E. coli and B. thuringiensis were investigated. This would help to make clear the secretion mechanism of VIP proteins and study the function of ADP-ribosyltransferase Vip2.     

Nutrient conditions determine the localization of Bacillus thuringiensis Vip3Aa protein in the mother cell compartment

Vip3Aa was first identified as a protein secreted during the vegetative growth phase of Bacillus thuringiensis (Bt) bacteria and which shows high insecticidal toxicity against lepidopteran insect pests (Estruch et al., 1996). Bt strains formulated as bio-insecticides only had low amounts of Vip3Aa secreted to the medium. Here, we report that Vip3Aa proteins produced by three different Bt strains, including an industrial strain, were indeed not secreted to the culture solution when grown in sporulation medium, but were retained in the mother cell compartment. In order to further investigate the Vip3Aa secretion and location, we grew the strains in rich medium. We found that in rich medium, a fraction of Vip3Aa was secreted, suggesting that Vip3Aa secretion is nutrient-dependent. Regardless of the growth conditions, we found that Vip3Aa retained in cell pellets exhibited high toxicity against Spodoptera frugiperda larvae. Hence, we speculate that the accumulation of Vip3Aa protein in the mother cell compartment under sporulation conditions could still be used as an efficient strategy for industrial production in commercial Bt strains.     

Characterization,cloning, expression and bioassay of vip3 gene isolated from an Egyptian Bacillus thuringiensis against whiteflies

Throughout the vegetative life of Bacillus thuringiensis, vegetative insecticidal proteins (Vip) are produced and secreted. In the present study, the vip3 gene isolated from Bacillus thuringiensis, an Egyptian isolate, was successfully amplified (2.4 kbp) and expressed using bacterial expression system. The molecular mass of the expressed protein was verified using SDS-PAGE and western blot analysis. Whiteflies were also screened for susceptibility to the expressed Vip3 protein (LC50). In addition, ST₅₀ was determined to assess the kill speed of the expressed Vip3 protein against whiteflies compared to the whole vegetative proteins. The results showed that the potency of whole B. thuringiensis vegetative proteins against whiteflies was slightly higher than the expressed Vip3 protein with 4.7-fold based on LC50 value. However, the ST50 parameter showed no significant difference between both the B. thuringiensis vegetative proteins and the expressed Vip3 alone. The results showed that the vip3 gene was successfully expressed in an active form which showed high susceptibility to whiteflies based on the virulence parameters LC₅₀ and ST₅₀. To our knowledge, this study showed for the first time the high toxicity of the expressed Vip3 proteins of B. thuringiensis toward whiteflies as a hopeful and promising bio-control agent.     

Specific primers for the detection of vip3A insecticidal gene within a Bacillus thuringiensis collection

A PCR-based method was developed for the rapid detection of vip3A gene encoding a novel Bacillus thuringiensis vegetative insecticidal protein with a wide spectrum of activities against lepidopteran insects. Specific primer combinations (three primers for the normal strand and two primers for the complementary strand) were capable of generating diagnostic fragments that successfully predicted the presence of the gene encoding the Vip3A insecticidal toxin in various B. thuringiensis strains. Specificity of amplicons generated by primer pairs was confirmed by restriction endonuclease digestion and DNA sequence analysis. The evaluation of B . thuringiensis strains for biological activity against insect pests of rice is thus aided by the grouping of strains based on their potential insecticidal spectrum.     

Study of the Bacillus thuringiensis Vip3Aa16 histopathological effects and determination of its putative binding proteins in the midgut of Spodoptera littoralis

The bacterium Bacillus thuringiensis produces, at the vegetative stage of its growth, Vip3A proteins with activity against a broad spectrum of lepidopteran insects. The Egyptian cotton leaf worm (Spodoptera littoralis) is an important agricultural pest that is susceptible to the Vip3Aa16 protein of Bacillus thuringiensis kurstaki strain BUPM95. The midgut histopathology of Vip3Aa fed larvae showed vacuolization of the cytoplasm, brush border membrane destruction, vesicle formation in the apical region and cellular disintegration. Biotinylated Vip3Aa toxin bound proteins of 55- and 100-kDa on blots of S. littoralis brush border membrane preparations. These binding proteins differ in molecular size from those recognized by Cry1C, one of the very few Cry proteins active against the polyphagous S. littoralis. This result supports the use of Vip3Aa16 proteins as insecticidal agent, especially in case of Cry-resistance management.     

苏云金芽孢杆菌新型营养期杀虫蛋白Vip3A研究

营养期杀虫蛋白（Vegetative Insecticidal Protein,Vip）Vip3A是苏云金芽孢杆菌（Bacillus thuringiensis,Bt）在营养生长对数中期分泌产生的一类新型杀虫蛋白。Vip3A广泛存在于Bt中,与晶体杀虫蛋白（Insecticidal Crystal Proteins,ICPs）没有任何同源性,不具有多样性,在遗传上比较保守。其N-端存在一趋化信号传导因子相似序列,C-端存在着纤维素结合结构域。Vip3A蛋白通过诱发细胞凋亡,最终导致细胞死亡,这与Bt δ-内毒素的作用机理完全不同。本文主要对Vip3A杀虫蛋白的发现、特性及作用机理作一简要综述。     

Characterization of Chimeric Bacillus thuringiensis Vip3 Toxins

Bacillus thuringiensis vegetative insecticidal proteins (Vip) are potential alternatives for B. thuringiensis endotoxins that are currently utilized in commercial transgenic insect-resistant crops. Screening a large number of B. thuringiensis isolates resulted in the cloning of vip3Ac1. Vip3Ac1 showed high insecticidal activity against the fall armyworm Spodoptera frugiperda and the cotton bollworm Helicoverpa zea but very low activity against the silkworm Bombyx mori. The host specificity of this Vip3 toxin was altered by sequence swapping with a previously identified toxin, Vip3Aa1. While both Vip3Aa1 and Vip3Ac1 showed no detectable toxicity against the European corn borer Ostrinia nubilalis, the chimeric protein Vip3AcAa, consisting of the N-terminal region of Vip3Ac1 and the C-terminal region of Vip3Aa1, became insecticidal to the European corn borer. In addition, the chimeric Vip3AcAa had increased toxicity to the fall armyworm. Furthermore, both Vip3Ac1 and Vip3AcAa are highly insecticidal to a strain of cabbage looper (Trichoplusia ni) that is highly resistant to the B. thuringiensis endotoxin Cry1Ac, thus experimentally showing for the first time the lack of cross-resistance between B. thuringiensis Cry1A proteins and Vip3A toxins. The results in this study demonstrated that vip3Ac1 and its chimeric vip3 genes can be excellent candidates for engineering a new generation of transgenic plants for insect pest control.     

Vip3A is responsible for the potency of Bacillus thuringiensis 9816C culture supernatant against Helicoverpa armigera and Spodoptera exigua

Culture supernatant of Bacillus thuringiensis 9816C had high toxicity against Helicoverpa armigera and Spodoptera exigua. However, it lost insecticidal activities after being bathed in boiling water for 5 min. Acrystalliferous mutants of Bt9816C (Bt9816C-NP1 and Bt9816C-NP2) cured of its endogenous plasmids no longer possessed vip3A gene and toxicity. The 89 kD protein which existed in Bt9816C supernatant disappeared in the two mutants' supernatant; nevertheless, the two mutants still exhibited hemolytic and phospholipase C activity as Bt9816C did. The vip3A gene of Bt9816C, vip3Aa18, was cloned and expressed in Escherichia coli BL21. Bioassay demonstrated that the recombinant E. coli had high toxicity against S. exigua. Taken together, it suggested that Vip3A protein was responsible for the toxicity of Bt9816C culture supernatants.     

Molecular characterization of a novel vegetative insecticidal protein from Bacillus thuringiensis effective against sap-sucking insect pest

Several isolates of Bacillus thuringiensis (Bt) were screened for the vegetative insecticidal protein (Vip) effective against sap-sucking insect pests. Screening results were based on LC(50) values against cotton aphid (Aphis gossypii), one of the dangerous pests of various crop plants including cotton. Among the isolates, the Bt#BREF24 showed promising results, and upon purification the aphidicidal protein was recognized as a binary toxin. One of the components of this binary toxin was identified by peptide sequencing to be a homolog of Vip2A that has been reported previously in other Bacillus spp. Vip2 belongs to the binary toxin group Vip1-Vip2, and is responsible for the enzymatic activity; and Vip1 is the translocation and receptor binding protein. The two genes encoding the corresponding proteins of the binary toxin, designated as vip2Ae and vip1Ae, were cloned from the Bt#BREF24, sequenced, and heterologously expressed in Escherichia coli. Aphid feeding assay with the recombinant proteins confirmed that these proteins are indeed the two components of the binary toxins, and the presence of both partners is essential for the activity. Aphid specificity of the binary toxin was further verified by ligand blotting experiment, which identified an ~50 kDa receptor in the brush border membrane vesicles of the cotton aphids only, but not in the lepidopteran insects. Our finding holds a promise of its use in future as a candidate gene for developing transgenic crop plants tolerant against sap-sucking insect pests.     

苏云金杆菌营养期杀虫蛋白的研究

营养期杀虫蛋白 (vegetativeinsecticidalproteins ,VIPs)是苏云金杆菌 (Bacillusthuringiensis,Bt)在对数生长中期分泌的一类新型杀虫毒蛋白。VIPs主要分为VIP1、VIP2和VIP3三种。VIP1和VIP2构成二元毒素 ,对鞘翅目叶甲科的昆虫具有杀虫特异性 ;而VIP3对鳞翅目昆虫具有较广谱的杀虫活性。VIP1和VIP2的杀虫作用机理还不清楚 ;VIP3通过诱发细胞凋亡 ,最终导致昆虫死亡 ,这种作用机理与Bt杀虫晶体蛋白的作用机理完全不同 ,这为筛选新的杀虫活性物质提供了新的思路。vip基因现已被应用于转基因杀虫植物的构建 ,得到高效抗虫的多价转基因玉米。此外 ,VIPs嵌合蛋白的构建、vip及其融合基因导入其它许多宿主微生物等方面的研究也具有诱人的潜在应用前景。     

Vegetative insecticidal protein enhancing the toxicity of Bacillus thuringiensis subsp kurstaki against Spodoptera exigua

AIMS: The objective of this work was to enhance the insecticidal activity or widen the pesticidal spectrum of a commercial Bacillus thuringiensis strain YBT1520. METHODS AND RESULTS: A vegetative insecticidal protein gene vip3Aa7, under the control of its native promoter and cry3A promoter, was subcloned into B. thuringiensis acrystalliferous BMB171 to generate BMB8901 and BMBvip respectively. It was found that the amount of Vip3Aa7 protein produced by BMBvip was 3.2-fold more than that produced by BMB8901. Therefore, the vip3Aa7 gene under the control of cry3A promoter was transformed into strain YBT1520. The toxicity of the resulting strain BMB218V against Spodoptera exigua was 10-fold more than that of YBT1520, and that the toxicity of BMB218V against Helicoverpa armigera retained the same level as that of strain YBT1520. CONCLUSIONS: Strain YBT1520 obtained high toxicity against S. exigua after it was transformed and expressed the foreign vip3Aa7 gene. SIGNIFICANCE AND IMPACT OF THE STUDY: Commercial B. thuringiensis strain YBT1520 has high toxicity against H. armigera and Plutella xylostella, but almost no activity against S. exigua, which is a major crop pest in China. This work provides a new strategy for widening the activity spectrum of B. thuringiensis against agriculture pests.