Construction of a Bacillus thuringiensis engineered strain with high toxicity and broad pesticidal spectrum against coleopteran insects

Insecticidal Activity of Bacillus thuringiensis Proteins Against Coleopteran Pests

Bacillus thuringiensis is the most successful microbial insecticide agent and its proteins have been studied for many years due to its toxicity against insects mainly belonging to the orders Lepidoptera, Diptera and Coleoptera, which are pests of agro-forestry and medical-veterinary interest. However, studies on the interactions between this bacterium and the insect species classified in the order Coleoptera are more limited when compared to other insect orders. To date, 45 Cry proteins, 2 Cyt proteins, 11 Vip proteins, and 2 Sip proteins have been reported with activity against coleopteran species. A number of these proteins have been successfully used in some insecticidal formulations and in the construction of transgenic crops to provide protection against main beetle pests. In this review, we provide an update on the activity of Bt toxins against coleopteran insects, as well as specific information about the structure and mode of action of coleopteran Bt proteins.

Effective bacterial insecticidal proteins against coleopteran pests: A review

Coleoptera, the order of insects commonly referred to as beetles, are able to survive in various environments, and thus, comprise the largest order in the animal kingdom. Coleopterans mainly include coprophagous and phytophagous lineages, and many species of the latter lineage are serious pests. In addition to traditional chemical methods, biocontrol measures using various bacterial insecticidal proteins have also gradually been developed to control these insect pests. In this review, we summarized the possible coleopteran-pest-specific bacteria and insecticidal proteins that have been reported in the literature thus far and have provided a comprehensive overview and long-term guidance for the control of coleopteran pests in the future.

Establishment and characterization of three new cell lines from the embryonic tissue of Holotrichia oblita Faldermann (Coleoptera: Scarabaeidae)

The establishment of new insect cell lines plays important roles in the researches of insect pathology, insect toxicology, insecticide screening and activity assay, etc. Using embryos of Holotrichia oblita Faldermann (Coleoptera: Scarabaeidae) as materials, this study describes the establishment of three cell lines designated as QAU-Ho-E-3 (Ho-3), QAU-Ho-E-4 (Ho-4), and QAU-Ho-E-6 (Ho-6), respectively. Currently, the three cell lines have been passaged more than 50 times in the TNM-FH insect cell medium containing 10% fetal bovine serum (FBS). All of them showed adherent growth. The majority of Ho-3 cells are spindle-shaped, with a size of 24.35 ± 5.29 × 11.56 ± 1.67 μm. The Ho-4 cells were either spindle-shaped or oblong, with a size of 38.07 ± 8.57 × 17.62 ± 2.48 μm. The Ho-6 cells were primarily round in shape with a diameter of 14.54 ± 1.96 μm. The Ho-3 and Ho-4 cell lines contained 20 chromosomes (i.e., diploid, 2n = 20) at passages 14 and 45. The Ho-6 cell line contained 20 chromosomes (i.e., diploid, 2n = 20) at passage 14 but 40 chromosomes (i.e., polyploidy, 4n = 40) at passage 45. The results of random amplified polymorphic DNA (RAPD) analysis showed that the RAPD fingerprint of the three cell lines was consistent with that of H. oblita eggs, but clearly different from that of BTI-Tn5B1-4 and Sf-9 cells, demonstrating that the three cell lines Ho-3, Ho-4, and Ho-6 are H. oblita cell lines. The results of the growth curve test showed that the population doubling times of Ho-3, Ho-4, and Ho-6 were 101.1, 105.2, and 83.6 h, respectively. The viral infection assay indicated that these H. oblita cell lines were not permissive to infection by Autographa californica multiple nucleopolyhedrovirus (AcMNPV) or Bombyx mori nucleopolyhedrovirus (BmNPV).

A chimeric cry8Ea1 gene flanked by MARs efficiently controls Holotrichia parallela

Peanuts transformed with the synthetic cry8Ea1 gene flanked by MARs are a potentially effective control strategy against white grubs. Cry8Ea1 protein levels of the construct containing MARs were increased by 2.5 times. White grubs are now recognized as the most important pests of peanut worldwide. A synthetic cry8Ea1 gene, which was toxic to Holotrichia parallela larvae, was expressed in chimeric peanut roots using an Agrobacterium rhizogenes-mediated transformation system. The relative mRNA and protein levels of the cry8Ea1 gene were confirmed by quantitative real-time PCR and ELISA, respectively. The effects of matrix attachment regions (MARs) on the expression and activity of the cry8Ea1 gene were analyzed. The average expression level of cry8Ea1 in peanut roots was higher for the plants harboring constructs flanked by MARs from tobacco. Moreover, differing from previous studies, the synthetic cry8Ea1 gene flanked by MARs showed more variation in protein levels than mRNA levels. These composite plants containing cry8Ea1 gene flanked by MARs exhibited a high toxicity against Holotrichia parallela larvae as shown by bioassay analysis, thus offering a potential effective combination to control subterranean insects in peanuts.

Cloning and characterization of a novel cry8Ab1 gene from Bacillus thuringiensis strain B-JJX with specific toxicity to scarabaeid (Coleoptera: Scarabaeidae) larvae

Isolation of Bacillus thuringiensis (Bt) strain or its cry gene encoding insecticidal crystal protein (ICP) with specific toxicity is of great importance to biological control of insect pests. In this study, by screening 66 strains of Bt isolated from soil samples collected in Shandong Province, China, a new cry8-type gene from Bt strain B-JJX was identified via PCR-RFLP method. This novel gene, cry8Ab1, was cloned from the Bt strain B-JJX and expressed in an acrystalliferous mutant strain HD-73(-). The open reading frame of the cry8Ab1 gene consists of 3543bp with a G+C content of 37.99% and encodes a protein of 1180 amino acids with a putative MW of 133.3kDa which was confirmed by SDS-PAGE analysis. The Cry8Ab1 protein was expressed and released as spherical parasporal crystals from Bt acrystalliferous mutant strain HD-73(-) along with the presence of spores. In bioassays, this protein was toxic to 3-day-old larvae of the scarabaeid pests, Holotrichia oblita and H. parallela, with an LC50 of 5.72 and 2.00μgtoxing(-1)soil, respectively. The results are in accordance with the insecticidal activities of the original Bt strain B-JJX, which had an LC50 of 1.72 and 0.96μgtoxing(-1)soil against H. oblita and H. parallela, respectively.

Molecular and biochemical characterization of two odorant-binding proteins from dark black chafer, Holotrichia parallela

The dark black chafer, Holotrichia parallela Motschulsky, is an economically important pest worldwide. Odorant-based lures and traps are being developed as a key kind of alternative control measures for this pest, and studies to reveal the mechanisms for chemotaxis in this pest are necessary. Two full-length cDNAs encoding different odorant-binding proteins (OBPs) were cloned. The predicted proteins were found to have the functional domains characteristic of typical OBPs and share a high degree of sequence similarity with OBP1 and OBP2 from other insects and were therefore designated as H. parallela OBP-1 and H. parallela OBP-2 (HparOBP-1 and HparOBP-2, respectively). These two OBPs were specifically expressed in antennae. The binding affinity of two purified proteins indicated that HparOBP-1 and HparOBP-2 could selectively interact with various volatiles emitted from host plants and pheromone components. Among the 10 chemicals tested, HparOBP-1 could bind to six of the tested compounds with a dissociation concentration (Ki) less than 20, and HparOBP-2 could bind to three of the compounds. The two OBPs are probably involved in chemotaxis of the dark black chafer. This discovery should accelerate research on chemical communications of this pest, which could potentially lead to the improvement of control measures based on lures and traps.

Bacillus thuringiensis: a century of research, development and commercial applications

Bacillus thuringiensis (Bt) is a soil bacterium that forms spores during the stationary phase of its growth cycle. The spores contain crystals, predominantly comprising one or more Cry and/or Cyt proteins (also known as δ-endotoxins) that have potent and specific insecticidal activity. Different strains of Bt produce different types of toxin, each of which affects a narrow taxonomic group of insects. Therefore, Bt toxins have been used as topical pesticides to protect crops, and more recently the proteins have been expressed in transgenic plants to confer inherent pest resistance. Bt transgenic crops have been overwhelmingly successful and beneficial, leading to higher yields and reducing the use of chemical pesticides and fossil fuels. However, their deployment has attracted some criticism particularly with regard to the potential evolution of pest-resistant insect strains. Here, we review recent progress in the development of Bt technology and the countermeasures that have been introduced to prevent the evolution of resistant insect populations.