Mosquito sex and mycobiota contribute to fructose metabolism in the Asian tiger mosquito Aedes albopictus

BACKGROUND

Plant floral nectars contain natural sugars such as fructose, which are a primary energy resource for adult mosquitoes. Despite the importance of carbohydrates for mosquito metabolism, a limited knowledge is available about the pathways involved in sugar assimilation by mosquitoes and their associated microbiota. To this end, we used ¹³C-metabolomic and stable isotope probing approaches coupled to high-throughput sequencing to reveal fructose-related mosquito metabolic pathways and the dynamics of the active gut microbiota following fructose ingestion.

RESULTS

Our results revealed significant differences in metabolic pathways between males and females, highlighting different modes of central carbon metabolism regulation. Competitive and synergistic interactions of diverse fungal taxa were identified within the active mycobiota following fructose ingestion. In addition, we identified potential cross-feeding interactions between this. Interestingly, there is a strong correlation between several active fungal taxa and the presence of fructose-derived metabolites.

CONCLUSIONS

Altogether, our results provide novel insights into mosquito carbohydrate metabolism and demonstrate that dietary fructose as it relates to mosquito sex is an important determinant of mosquito metabolism; our results also further highlight the key role of active mycobiota interactions in regulating the process of fructose assimilation in mosquitoes. This study opens new avenues for future research on mosquito-microbiota trophic interactions related to plant nectar-derived sugars. Video abstract.

Comparative Analysis of the Bacterial and Fungal Communities in the Gut and the Crop of Aedes albopictus Mosquitoes: A Preliminary Study

The Asian tiger mosquito Aedes albopictus is a major pathogen vector and one of the world’s most invasive species. In recent years, the study of mosquito-associated microbiota has received growing interest for reducing transmission of mosquito-borne pathogens. Most of studies on mosquito microbiota mainly focused on the gut bacteria. However, microorganisms can also colonize other organs and are not restricted to bacteria. In mosquitoes, the crop is the primary storage organ for sugars from the nectar feeding before it is transferred into the midgut for digestion. No study has yet investigated whether this organ can harbor microorganisms in Ae. albopictus. By using high-throughput sequencing, this study is the first to describe the microbiota including both bacteria and fungi in sugar-fed Ae. albopictus males and females. The results showed the presence of diverse and rich bacterial and fungal communities in the crop of both sexes that did not strongly differ from the community composition and structure found in the gut. Altogether, our results provide a thorough description of the crop-associated microbiota in Ae. albopictus which can open new avenues for further studies on trophic interactions between the mosquito and its microbiota.

Who is eating fructose within the Aedes albopictus gut microbiota?

The Asian tiger mosquito Aedes albopictus is a major public health concern because of its invasive success and its ability to transmit pathogens. Given the low availability of treatments against mosquito-borne diseases, vector control remains the most suitable strategy. The methods used thus far are becoming less effective, but recent strategies have emerged from the study of mosquito-associated microorganisms. Although the role of the microbiota in insect biology does not require further proof, much remains to be deciphered in mosquitoes, especially the contribution of the microbiota to host nutrient metabolism. Mosquitoes feed on plant nectar, composed of mostly fructose. We used stable isotope probing to identify bacteria and fungi assimilating fructose within the gut of Ae. albopictus. Mosquitoes were fed a ¹³ C-labelled fructose solution for 24 h. Differences in the active microbial community according to the sex of mosquitoes were highlighted. The bacterium Lelliottia and the fungi Cladosporium and Aspergillus dominated the active microbiota in males, whereas the bacterium Ampullimonas and the yeast Cyberlindnera were the most active in females. This study is the first to investigate trophic interactions between Ae. albopictus and its microbiota, thus underscoring the importance of the microbial component in nectar feeding in mosquitoes.

Short-term impacts of anthropogenic stressors on Aedes albopictus mosquito vector microbiota

Recent studies have highlighted the potential role of microbiota in the biology of the Aedes albopictus mosquito vector. This species is highly anthropogenic and exhibits marked ecological plasticity, with a resulting high potential to colonize a wide range of habitats-including anthropized areas-under various climatic conditions. We put forward the hypothesis that climate and anthropogenic activities, such as the use of antibiotics in agriculture and human medicine, might affect the mosquito-associated bacterial community. We thus studied the additive impact of a temperature decrease and antibiotic ingestion on the temporal dynamics of Ae. albopictus survival and its associated bacterial communities. The results showed no effects of disturbances on mosquito survival. However, short-term temperature impacts on bacterial diversity were observed, while both the community structure and bacterial diversity were affected by early antibiotic ingestion. The genera Elizabethkingia, Chryseobacterium and Wolbachia, as well as an unclassified member of the Bacteroidales order were particularly affected. Antibiotics negatively impacted Elizabethkingia abundance, while Chryseobacterium was completely eliminated following both disturbances, to the benefit of Wolbachia and the unclassified Bacteroidales species. These results generated fresh insight into the effects of climate and anthropogenic activities such as the use of antibiotics on mosquito microbiota.

The mosquito holobiont: fresh insight into mosquito-microbiota interactions

The holobiont concept was first developed for coral ecosystems but has been extended to multiple organisms, including plants and other animals. Studies on insect-associated microbial communities have produced strong evidence that symbiotic bacteria play a major role in host biology. However, the understanding of these symbiotic relationships has mainly been limited to phytophagous insects, while the role of host-associated microbiota in haematophagous insect vectors remains largely unexplored. Mosquitoes are a major global public health concern, with a concomitant increase in people at risk of infection. The global emergence and re-emergence of mosquito-borne diseases has led many researchers to study both the mosquito host and its associated microbiota. Although most of these studies have been descriptive, they have led to a broad description of the bacterial communities hosted by mosquito populations. This review describes key advances and progress in the field of the mosquito microbiota research while also encompassing other microbes and the environmental factors driving their composition and diversity. The discussion includes recent findings on the microbiota functional roles and underlines their interactions with the host biology and pathogen transmission. Insight into the ecology of multipartite interactions, we consider that conferring the term holobiont to the mosquito and its microbiota is useful to get a comprehensive understanding of the vector pathosystem functioning so as to be able to develop innovative and efficient novel vector control strategies.

Reflex control of the retractor bulbi muscle in the cat

The effects of vestibular and trigeminal stimulation on reflex responses of each slip of the retractor bulbi muscle were tested by recording the electromyogram. 1. In "encéphale isolé" cat, phasic electrical stimulation of the horizontal canal induced no response in the RB slips. Repetitive vestibular stimulation did not produce nystagmus in the RB muscle while strong muscular discharges were observed in the nystagmus lateral rectus muscle. 2. In anaesthetized cats, three trigeminal inputs elicited strong reflex responses in each slip of the RB muscle. Electrical stimulation of the vibrissae or the infra-orbital nerve evoked a two component reflex response (latencies: 5 ms +/- 0.5 and 14 ms +/- 2). Electrical stimulation of the supraorbital nerve elicited a single component reflex response (latency: 6 ms +/- 0.5). Electrical stimulation of the long ciliary nerves evoked a complex response with four components (latencies: 7.5 ms +/- 0.5, 10 ms +/- 2, 15 ms +/- 2,20 ms +/- 2). 3. Pentobarbital and morphine produced lasting depression of the reflex responses of the RB muscle. The depressive effect of morphine was reversed by naloxone.

[Localization of motoneurones of retractor bulbi muscles by retrograde transport of exogenous peroxidase in cats]

Retrograde transport of exogene horseradish peroxidase has been used to localize the retractor bulbi muscle motoneurones. These motoneurones are located ventro-laterally in the tegmental reticular field; they are grouped in a rostro-caudal column above the superior olive. They correspond to the accessory nucleus of the VIe nerve described by old anatomists.