Bacillus thuringiensis Cry11Ba works synergistically with Cry4Aa but not with Cry11Aa for toxicity against mosquito Culex pipiens (Diptera: Culicidae) larvae

Abstract

A 2175-bp modified gene (cry11Ba-S1) encoding Cry11Ba from Bacillus thuringiensis subsp. jegathesan was designed and the recombinant protein was expressed as a fusion protein with glutathione S-transferase in Escherichia coli. The recombinant Cry11Ba was highly toxic against Culex pipiens mosquito larvae, being 9 and 17 times more toxic than mosquitocidal Cry4Aa and Cry11Aa from B. thuringiensis subsp. israelensis, respectively. Interestingly, a further increase in the toxicity of the recombinant Cry11Ba was achieved by mixing with Cry4Aa, but not with Cry11Aa. These findings suggested that Cry11Ba worked synergistically with Cry4Aa, but not with Cry11Aa, in exhibiting toxicity against C. pipiens larvae. On the other hand, the amount of Cry toxin bound to brush border membrane vesicles (BBMVs) did not significantly change between individual toxins and the toxin mixtures, suggesting that the increase in toxins binding to BBMVs was not a reason for the observed synergistic effect. It is generally accepted that synergism of toxins is a potentially powerful tool for enhancing insecticidal activity and managing Cry toxin-resistance in mosquitoes. The mixture of Cry4Aa and Cry11Ba in order to increase toxicity would be very valuable in terms of mosquito control.

Characteristics of channel pores formed by Bacillus thuringiensis mosquito-larvicidal Cry4Aa toxin

“…Cry4Aa acts synergistically with Cry11Ba from B. thuringiensis subsp. jegathesan (Hayakawa et al 2017a) and Cry46Ab from B. thuringiensis TK-E6 (Hayakawa et al 2017b) in terms of toxicity against C. pipiens mosquito larvae. These observations suggest that the modes of action of the Bti Cry toxins (i.e., Cry4Aa, Cry4Ba, and Cry11Aa) differ.…”

Recent advancement on chemical arsenal of Bt toxin and its application in pest management system in agricultural field

“…Several investigations have reported the low toxicity of Cyt1Aa and of Cyt2Aa produced by Bt kyushuensis; however, their combined insecticidal effect is very high (Ben-Dov 2014;Deist et al 2014). Similar synergistic effect of Bti Cry toxins-Cyt1Aa and Cyt toxins-Cry toxins against several insect pests, including Culex quinquefasciatus, also have been studies (Sena et al 2009;Hayakawa et al 2016).…”

New native Bacillus thuringiensis strains induce high insecticidal action against Culex pipiens pallens larvae and adults

“…The combination of the Cry4, Cry10, Cry11, and Cyt toxins are known to have a potent activity against mosquitoes [ 69 ]. Combinations of Cry4Aa with Cry11Ba proteins have been found to interact synergistically with a significant high toxicity against mosquito species Culex pipiens [ 70 ]. Interesting, this combination was detected in the B. thuringiensis A4, A8, A10 and B6 strains, when the cry4Aa with cry11Ba genes were analyzed.…”