Bacillus sphaericus exposure reduced vector competence of Anopheles dirus to Plasmodium yoelii by upregulating the Imd signaling pathway

Abstract

Background: Vector control with Bacillus sphaericus (Bs) is an effective way to block the transmission of malaria. However, in practical application of Bs agents, a sublethal dose effect was often caused by insufficient dosing, and it is little known whether the Bs exposure would affect the surviving mosquitoes' vector capacity to malaria. Methods: A sublethal dose of the Bs 2362 strain was administrated to the early fourth-instar larvae of Anopheles dirus to simulate shortage use of Bs in field circumstance. To determine vector competence, mosquitoes were dissected and the oocysts in the midguts were examined on day 9-11 post-infection with Plasmodium yoelii. Meanwhile, a SYBR quantitative PCR assay was conducted to examine the transcriptional level of the key immune molecules of mosquitoes, and RNA interference was utilized to validate the role of key immune effector molecule TEP1. Results: The sublethal dose of Bs treatment significantly reduced susceptibility of An. dirus to P. yoelii, with the decrease of P. yoelii infection intensity and rate. Although there existed a melanization response of adult An. dirus following challenge with P. yoelii, it was not involved in the decrease of vector competence as no significant difference of melanization rates and densities between the control and Bs groups was found. Further studies showed that Bs treatment significantly increased TEP1 expression in the fourth-instar larvae (L4), pupae (Pu), 48 h post-infection (hpi) and 72 hpi (P < 0.001). Further, gene-silencing of TEP1 resulted in disappearance of the Bs impact on vector competence of An. dirus to P. yoelii. Moreover, the transcriptional level of PGRP-LC and Rel2 were significantly elevated by Bs treatment with decreased expression of the negative regulator Caspar at 48 hpi, which implied that the Imd signaling pathway was upregulated by Bs exposure. Conclusions: Bs exposure can reduce the vector competence of An. dirus to malaria parasites through upregulating Imd signaling pathway and enhancing the expression of TEP1. The data could not only help us to understand the impact and mechanism of Bs exposure on Anopheles' vector competence to malaria but also provide us with novel clues for wiping out malaria using vector control.

Bacterial Toxins Active against Mosquitoes: Mode of Action and Resistance

“…The microbiota can play a major role in the antiviral response of mosquitoes, either by secreting antiviral or proviral molecules or by modulating the immunity response [ 401 , 402 , 403 , 404 ]. Some studies have shown alterations in the susceptibility to arbovirus or protozoa in mosquitoes exposed to sublethal doses of L. sphaericus or Bti [ 404 , 405 , 406 , 407 ]. Therefore, a broader analysis of the potential impact of L. sphaericus and Bti on mosquito biology is required to assess the consequences of their use beyond the issue of resistance onset.…”

Capsaicin decreases fecundity in the Asian malaria vector Anopheles stephensi by inhibiting the target of rapamycin signaling pathway

“…stephensi Hor strain was maintained at 28 °C and 70–80% relative humidity with a 12-h light/dark photocycle, according to the standard rearing procedures in the laboratory. The adults and larvae were fed on 10% sugar solution and a powdered mix of dry degreased pork liver and yeast at a ratio of 1:4, respectively [ 19 ].…”

Self-Healing Cement: A Review

“…This is due to the differentiation in cell wall structure between Gram-positive and Gram-negative bacteria. A relatively large set of bacteria can be used for this purpose, such as Bacillus pasteurii [31], Bacillus sphaericus [32], Escherichia coli [33], Bacillus subtilus [34], Bacillus cohnii [35], Bacillus pseudofirmus [36], and Bacillus halodurans [27]. In this paper, however, we will limit our selection for the sake of clarity.…”