Bacillus thuringiensis subsp. israelensis (Bti) has been used in the field for over twenty years without resistance development in any target insect. In contrast, mosquito resistance to B. sphaericus has been observed in the field in many countries. This remarkable difference in the propensity to develop resistance to two mosquitocidal Bacillus strains is likely due to the presence of multiple toxins in Bti. However, mosquitoes are able to rapidly develop resistance to individual toxins from this strain. A major reason for the apparent inability of mosquitoes to develop resistance to Bti is the presence of cytolytic (Cyt) toxins in this and other mosquitocidal strains. During the last grant period we showed that key to the lack of mosquito resistance to Bti was how two toxins in this strain, namely Cry11A and Cyt1A toxins interact. We showed Cyt1A acts as a surrogate receptor for Cry11Aa. Importantly Cyt1Aa binds through Cry11A loop domains that are also involved in binding endogenous Aedes aegypti receptor proteins. Our research showed Aedes receptor proteins include cadherin, alkaline phosphatases (ALP), and aminopeptidases (APNs). All three classes bind mosquitocidal toxins with relatively high affinity, unlike in lepidopterans where only cadherin binds with high affinity. This implies both APN and ALP of mosquitoes could act as primary rather than as secondary receptors as in moths, suggesting a possible difference in the mode of action of mosquitocidal and lepidopteran Cry toxins. We believe however, there is conservation in the mode of action of Bt Cry toxins. Therefore we hypothesize a similar mode of action of action occurs in mosquitoes as in lepidopterans. In this proposal we plan to test this hypothesis. Consequently, we hypothesize that: (i) cadherin is a key protein which mediates initial binding to mosquitocidal Cry toxins and is essential for larval toxicity;ii) ALPs (and APNs) act as secondary receptors that allow toxin targeting to the cell membrane. Also in the previous proposal we showed Cyt1A plays a critical role in acting as a surrogate receptor for Cry11Aa. We therefore hypothesize that (iii) Cyt1A also is a receptor for other Cry toxins in Bti, and synergizes the toxicity of mosquitocidal Cry toxins. We will test this hypothesis and also elucidate the mechanism by which Cyt toxins insert into the membrane to act as surrogate receptors. This project is also a proposal to continue a successful collaboration between three different investigators to best use the expertise of each laboratory.

Public Health Relevance

B. thuringiensis subsp. israelensis are used for control of human disease vectors, such as species of Simulium, Aedes, Culex, and Anopheles. Elucidating mechanisms of Cry toxin action in aids our understanding of how mosquito and black fly control is achieved and also enables us to determine mechanisms by which resistance can occur. This mode of Cyt1A toxin action investigation also illuminates mechanism of synergism between mosquitocidal Cry and Cyt toxins. Finally, elucidation of mechanisms by which the Cyt1Aa toxin acts also will help us understand how other cytolytic toxins of human health significance cause toxicity.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI066014-08
Application #
8294971
Study Section
Vector Biology Study Section (VB)
Program Officer
Costero, Adriana
Project Start
2005-07-01
Project End
2015-06-30
Budget Start
2012-07-01
Budget End
2013-06-30
Support Year
8
Fiscal Year
2012
Total Cost
$480,558
Indirect Cost
$122,958
Name
University of California Riverside
Department
Anatomy/Cell Biology
Type
Schools of Earth Sciences/Natur
DUNS #
627797426
City
Riverside
State
CA
Country
United States
Zip Code
92521
Lee, Su-Bum; Chen, Jianwu; Aimanova, Karlygash G et al. (2015) Aedes cadherin mediates the in vivo toxicity of the Cry11Aa toxin to Aedes aegypti. Peptides 68:140-7
Qureshi, Nadia; Chawla, Swati; Likitvivatanavong, Supaporn et al. (2014) The cry toxin operon of Clostridium bifermentans subsp. malaysia is highly toxic to Aedes Larval Mosquitoes. Appl Environ Microbiol 80:5689-97
Cantón, Pablo Emiliano; López-Díaz, Jazmin A; Gill, Sarjeet S et al. (2014) Membrane binding and oligomer membrane insertion are necessary but insufficient for Bacillus thuringiensis Cyt1Aa toxicity. Peptides 53:286-91
Gómez, Isabel; Sánchez, Jorge; Muñoz-Garay, Carlos et al. (2014) Bacillus thuringiensis Cry1A toxins are versatile proteins with multiple modes of action: two distinct pre-pores are involved in toxicity. Biochem J 459:383-96
Lee, Su-Bum; Aimanova, Karlygash G; Gill, Sarjeet S (2014) Alkaline phosphatases and aminopeptidases are altered in a Cry11Aa resistant strain of Aedes aegypti. Insect Biochem Mol Biol 54:112-21
Chen, Jianwu; Likitvivatanavong, Supaporn; Aimanova, Karlygash G et al. (2013) A 104 kDa Aedes aegypti aminopeptidase N is a putative receptor for the Cry11Aa toxin from Bacillus thuringiensis subsp. israelensis. Insect Biochem Mol Biol 43:1201-8
Rodriguez-Almazan, Claudia; Reyes, Esmeralda Z; Zuniga-Navarrete, Fernando et al. (2012) Cadherin binding is not a limiting step for Bacillus thuringiensis subsp. israelensis Cry4Ba toxicity to Aedes aegypti larvae. Biochem J 443:711-7
Porta, Helena; Cancino-Rodezno, Angeles; Soberon, Mario et al. (2011) Role of MAPK p38 in the cellular responses to pore-forming toxins. Peptides 32:601-6
Likitvivatanavong, Supaporn; Chen, Jianwu; Evans, Amy M et al. (2011) Multiple receptors as targets of Cry toxins in mosquitoes. J Agric Food Chem 59:2829-38
Likitvivatanavong, Supaporn; Chen, Jianwu; Bravo, Alejandra et al. (2011) Cadherin, alkaline phosphatase, and aminopeptidase N as receptors of Cry11Ba toxin from Bacillus thuringiensis subsp. jegathesan in Aedes aegypti. Appl Environ Microbiol 77:24-31

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