Delayed larval development in Anopheles mosquitoes deprived of Asaia bacterial symbionts

<p>Abstract</p> <p>Background</p> <p>In recent years, acetic acid bacteria have been shown to be frequently associated with insects, but knowledge on their biological role in the arthropod host is limited. The discovery that acetic acid bacteria of the genus <it>Asaia</it> are a main component of the microbiota of <it>Anopheles stephensi</it> makes this mosquito a useful model for studies on this novel group of symbionts. Here we present experimental results that provide a first evidence for a beneficial role of <it>Asaia</it> in <it>An. stephensi</it>.</p> <p>Results</p> <p>Larvae of <it>An. stephensi</it> at different stages were treated with rifampicin, an antibiotic effective on wild-type <it>Asaia</it> spp., and the effects on the larval development were evaluated. Larvae treated with the antibiotic showed a delay in the development and an asynchrony in the appearance of later instars. In larvae treated with rifampicin, but supplemented with a rifampicin-resistant mutant strain of <it>Asaia</it>, larval development was comparable to that of control larvae not exposed to the antibiotic. Analysis of the bacterial diversity of the three mosquito populations confirmed that the level of <it>Asaia</it> was strongly decreased in the antibiotic-treated larvae, since the symbiont was not detectable by PCR-DGGE (denaturing gradient gel electrophoresis), while <it>Asaia</it> was consistently found in insects supplemented with rifampicin plus the antibiotic-resistant mutant in the diet, and in those not exposed to the antibiotic.</p> <p>Conclusions</p> <p>The results here reported indicate that <it>Asaia</it> symbionts play a beneficial role in the normal development of <it>An. stephensi</it> larvae.</p

Chapter Facing Malaria Parasite with Mosquito Symbionts

Optical physic

Facing Malaria Parasite with Mosquito Symbionts

Optical physic

Inhibition of Asaia in adult mosquitoes causes male-specific mortality and diverse transcriptome changes

Mosquitoes can transmit many infectious diseases, such as malaria, dengue, Zika, yellow fever, and lymphatic filariasis. Current mosquito control strategies are failing to reduce the severity of outbreaks that still cause high human morbidity and mortality worldwide. Great expectations have been placed on genetic control methods. Among other methods, genetic modification of the bacteria colonizing different mosquito species and expressing anti-pathogen molecules may represent an innovative tool to combat mosquito-borne diseases. Nevertheless, this emerging approach, known as paratransgenesis, requires a detailed understanding of the mosquito microbiota and an accurate characterization of selected bacteria candidates. The acetic acid bacteria Asaia is a promising candidate for paratransgenic approaches. We have previously reported that Asaia symbionts play a beneficial role in the normal development of Anopheles mosquito larvae, but no study has yet investigated the role(s) of Asaia in adult mosquito biology. Here we report evidence on how treatment with a highly specific anti-Asaia monoclonal antibody impacts the survival and physiology of adult Anopheles stephensi mosquitoes. Our findings offer useful insight on the role of Asaia in several physiological systems of adult mosquitoes, where the influence differs between males and females

Time-resolved assembly of a nucleoprotein complex between Shigella flexneri virF promoter and its transcriptional repressor H-NS.

The virF gene of Shigella, responsible for triggering the virulence cascade in this pathogenic bacterium, is transcriptionally repressed by the nucleoid-associated protein H-NS. The primary binding sites of H-NS within the promoter region of virF have been detected here by footprinting experiments in the presence of H-NS or its monomeric DNA-binding domain (H-NSctd), which displays the same specificity as intact H-NS. Of the 14 short DNA fragments identified, 10 overlap sequences similar to the H-NS binding motif. The 'fast', 'intermediate' and 'slow' H-NS binding events leading to the formation of the nucleoprotein complex responsible for transcription repression have been determined by time-resolved hydroxyl radical footprinting experiments in the presence of full-length H-NS. We demonstrate that this process is completed in ≤1 s and H-NS protections occur simultaneously on site I and site II of the virF promoter. Furthermore, all 'fast' protections have been identified in regions containing predicted H-NS binding motifs, in agreement with the hypothesis that H-NS nucleoprotein complex assembles from a few nucleation sites containing high-affinity binding sequences. Finally, data are presented showing that the 22-bp fragment corresponding to one of the HNS binding sites deviates from canonical B-DNA structure at three TpA steps

Symbiotic Control of mosquito borne disease

It is well accepted that the symbiotic relationships insects have established with several microorganisms have had a key role in their evolutionary success. Bacterial symbiosis is also prevalent in insects that are efficient disease vectors, and numerous studies have sought to decrypt the basic mechanisms of the host-symbiont relationships and develop ways to control vector borne diseases. "Symbiotic control", a new multi-faceted approach that uses symbiotic microorganisms to control insect pests or reduce vector competence, seems particularly promising. Three such approaches currently at the cutting edge are: i) the disruption of microbial symbionts required by insect pests; ii) the manipulation of symbionts that can express anti-pathogen molecules within the host; and iii) the introduction of endogenous microbes that affect life-span and vector capacity of the new hosts in insect populations. This work reviews current knowledge on microbial symbiosis in mosquitoes that holds promise for development of symbiotic control for mosquito borne diseases

Bacterial Symbionts in Aedes aegypti and Aedes albopictus.

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A <i>Wickerhamomyces anomalus</i> Killer Strain in the Malaria Vector <i>Anopheles stephensi</i>

<div><p>The yeast <i>Wickerhamomyces anomalus</i> has been investigated for several years for its wide biotechnological potential, especially for applications in the food industry. Specifically, the antimicrobial activity of this yeast, associated with the production of Killer Toxins (KTs), has attracted a great deal of attention. The strains of <i>W. anomalus</i> able to produce KTs, called “killer” yeasts, have been shown to be highly competitive in the environment. Different <i>W. anomalus</i> strains have been isolated from diverse habitats and recently even from insects. In the malaria mosquito vector <i>Anopheles stephensi</i> these yeasts have been detected in the midgut and gonads. Here we show that the strain of <i>W. anomalus</i> isolated from <i>An. stephensi</i>, namely <i>Wa</i>F17.12, is a killer yeast able to produce a KT in a cell-free medium (<i>in vitro</i>) as well as in the mosquito body (<i>in vivo</i>). We showed a constant production of <i>Wa</i>F17.12-KT over time, after stimulation of toxin secretion in yeast cultures and reintroduction of the activated cells into the mosquito through the diet. Furthermore, the antimicrobial activity of <i>Wa</i>F17.12-KT has been demonstrated <i>in vitro</i> against sensitive microbes, showing that strain <i>Wa</i>F17.12 releases a functional toxin. The mosquito-associated yeast <i>Wa</i>F17.12 thus possesses an antimicrobial activity, which makes this yeast worthy of further investigations, in view of its potential as an agent for the symbiotic control of malaria.</p></div