Mosquitoes that transmit many deadly infectious diseases also need to keep fighting against many microbial infections. Constitutive expression of multiple antimicrobial peptides (AMPs) in almost all body tissues is believed to facilitate the effective management of these local infections. When any infection breaches the local barrier, AMPs are induced rapidly in non-target tissues such as hemocytes (HCs) and establish their co-ordination with systemic immune effectors to clear off the body infection. But how interorgan immune communication is managed during local and systemic infections remain largely unknown. To understand this interorgan molecular relationship, we identified, extensively profiled and compared the expression of AMPs in three important mosquito tissues viz. midgut, fat body (FB), and HCs. dsRNA-mediated AMPs silencing suggests that mosquito tissues are able to manage an optimal expression of AMPs at the physiological level. We also examined the possible contribution of two important immune regulator genes relish (REL) and nitric oxide synthase, controlling AMPs expression in these tissues during local or systemic infections. We show that each tissue has a unique ability to respond to local/systemic challenges, but HCs are more specialized to recognize and discriminate-specific antigens than gut and FB. Our investigation also revealed that both REL and NO participate in the overall management of the interorgan immune responses, but at the same time each tissue also has its own ability to maintain the interorgan flow of signals. In our knowledge, this is the first large-scale study examining the interorgan immune relationship in the mosquito.

The periodic ingestion of a protein-rich blood meal by adult female mosquitoes causes a drastic metabolic change in their innate physiological status, which is referred to as a ‘metabolic switch’. While understanding the neural circuits for host-seeking is modestly attended, how the gut ‘metabolic switch’ modulates brain functions, and resilience to physiological homeostasis, remains unexplored. Here, through a comparative brain RNA-Seq study, we demonstrate that the protein-rich diet induces the expression of brain transcripts related to mitochondrial function and energy metabolism, possibly causing a shift in the brain’s engagement to manage organismal homeostasis. A dynamic mRNA expression pattern of neuro-signaling and neuro-modulatory genes in both the gut and brain likely establishes an active gut–brain communication. The disruption of this communication through decapitation does not affect the modulation of the neuro-modulator receptor genes in the gut. In parallel, an unusual and paramount shift in the level of neurotransmitters (NTs), from the brain to the gut after blood feeding, further supports the idea of the gut’s ability to serve as a ‘second brain’. After blood-feeding, a moderate enrichment of the gut microbial population, and altered immunity in the gut of histamine receptor-silenced mosquitoes, provide initial evidence that the gut-microbiome plays a crucial role in gut–brain–axis communication. Finally, a comparative metagenomics evaluation of the gut microbiome highlighted that blood-feeding enriches the family members of the Morganellaceae and Pseudomonadaceae bacterial communities. The notable observation of a rapid proliferation of Pseudomonas bacterial sp. and tryptophan enrichment in the gut correlates with the suppression of appetite after blood-feeding. Additionally, altered NTs dynamics of naïve and aseptic mosquitoes provide further evidence that gut-endosymbionts are key modulators for the synthesis of major neuroactive molecules. Our data establish a new conceptual understanding of microbiome–gut–brain–axis communication in mosquitoes.

Periodic ingestion of a protein-rich blood meal by adult female mosquitoes causes a drastic metabolic change in their innate physiological status, which is referred to as ‘metabolic switch. Although the down-regulation of olfactory factors is key to restrain host-attraction, how the gut ‘metabolic switch’ modulates brain functions, and resilience physiological homeostasis remains unexplored. Here, we demonstrate that the protein-rich diet induces mitochondrial function and energy metabolism, possibly shifting the brain’s engagement to manage organismal homeostasis. A dynamic expression pattern of neuro-signaling and neuro-modulatory genes in both the brain and gut indicates an optimal brain-distant organ communication. Even after decapitation, significant modulation of the neuro-modulator receptor genes as well as quantitative estimation of neurotransmitters (NTs), together confer the gut’s ability to serve as a ‘second brain’. Finally, data on comparative metagenomic analysis and altered NTs dynamics of naïve and aseptic mosquitoes provide the initial evidence that gut-endosymbionts are key modulators for the synthesis of major neuroactive molecules. Conclusively, our data establish a new conceptual understanding of microbiome-gut-brain-axis communication in mosquitoes. Abstract Figure: Graphical Highlights: Highly proteinaceous blood meal uptake causes gut ‘metabolic switch’ activity in mosquitoes. Gut’s calling shifts the brain’s administrative function from external communication to inter-organ management. ‘Gut’, as a ‘Second brain’ plays a crucial role in the maintenance of physiological homeostasis. Metabolic switch and proliferation of symbiotic bacteria establish microbiome-gut-brain axis communication in mosquitoes.

Mosquitoes rely exclusively on blood-derived sterols, transported by sterol carrier protein (SCP), for reproduction and metabolic regulation. SCP expression is strongly induced after blood feeding and dynamically modulated during Plasmodium vivax infection—upregulated in the midgut and salivary glands but suppressed in hemocytes—indicating that parasite infection modulates the host sterol transport and metabolism. RNAi-mediated knockdown of SCP significantly reduced mosquito fecundity, underscoring its vital role in reproductive physiology. These findings highlight SCP as a key metabolic regulator linking nutrient uptake to reproductive outcome, while its Plasmodium infection-driven modulation may facilitate the parasite growth. While reproduction remains the primary physiological outcome, the metabolic modulation of SCP during infection also points to it as a possible transmission-blocking target in integrated malaria control strategies.

Decoding the molecular basis of host seeking and blood feeding behavioral evolution/adaptation in the adult female mosquito may provide an opportunity to design new molecular strategy to disrupt human-mosquito interactions. However, despite the great progress in the field of mosquito olfaction and chemo-detection, little is known that how the sex-specific specialization of the olfactory system enables adult female mosquitoes to derive and manage complex blood feeding associated behavioral responses. A comprehensive RNAseq analysis of prior and post blood meal olfactory system of An. culicifacies mosquito revealed that a minor but unique change in the nature and regulation of key olfactory genes play a pivotal role in managing diverse behavioral responses. Age dependent transcriptional profiling demonstrated that adult female mosquito’s chemosensory system gradually learned and matured to drive the host-seeking and blood feeding behavior at the age of 5-6 days. A zeitgeber time scale expression analysis of Odorant Binding Proteins (OBPs) unravels unique association with a late evening to midnight peak biting time. Blood meal-induced switching of unique sets of OBP genes and Odorant Receptors (ORs) expression coincides with the change in the innate physiological status of the mosquitoes. Blood meal follows up experiments provide enough evidence that how a synergistic and concurrent action of OBPs-ORs may drive ‘prior and post blood meal’ complex behavioral events. Finally, tissue-specific gene expression analysis and molecular modelling predicted two uncharacterized novel sensory appendages proteins (SAP-1 & SAP2) unique to An. culicifacies mosquito and may play a central role in the host-seeking behavior. Significance: Evolution and adaptation of blood feeding behavior not only favored the reproductive success of adult female mosquito but also make them an important disease vectors. Immediately after emergence, an environmental exposure may favor the broadly tuned olfactory system of mosquitoes to derive complex behavioral responses. But, how these olfactory derived genetic factors manage female specific ‘pre and post’ blood meal associated complex behavioral responses are not well known. We unraveled synergistic actions of olfactory factors governs an innate to prime learning strategy to facilitate rapid blood meal acquisition and downstream behavioral activities. A species-specific transcriptional profiling and an in-silico analysis predict novel ‘sensory appendages protein’, as a unique target to design disorientation strategy against the mosquito Anopheles culicifacies .

Blood feeding-enriched gut-microbiota boosts mosquitoes’ anti- Plasmodium immunity. Here, we ask how Plasmodium vivax alters microbiota, anti- Plasmodial immunity and impact tripartite Plasmodium -mosquito-microbiota interactions in the gut lumen. Using a metagenomics analysis, we predominantly detect Elizabethkingia meningitis and Pseudomonas sps. in naïve mosquitoes. Naïve blood fed gut shows a heightened presence of Elizabethkingia , Pseudomonas and Serratia . A parallel RNAseq analysis of blood-fed midguts identify Elizabethkingia -transcripts, which may have role in iron metabolism. Post, a Plasmodium vivax infected blood-meal, however, we do not detect bacterial until circa 36 hours. Intriguingly, transcriptional expression of a selected array of antimicrobial arsenal cecropins 1-2, defensin-1 and gambicin remains low during the first 36 hours–a time frame when ookinietes/early oocysts invade gut. We conclude during the preinvasive phase, Plasmodium vivax outcompetes midgut-microbiota. Suppression of important immune factors, likely due to altered microbiota, may enhance Plasmodium vivax survival. Additional finding of a novel Wolbachia association warrants further research to design ‘paratransgenesis’ tools for malaria control. Author Summary: Successful malaria transmission relies on the competitive interactions of Plasmodium and mosquito’s tissue specific immune potential. Within 24hrs of blood meal gut-microbiota grows exponentially and lead to robust enhancement of mosquito immune response, which is detrimental to parasite survival and development. But the mechanism how Plasmodium manages to evade this pre-invasive immune barrier is not well known. We investigated the influence of tripartite gut-microbiome-parasite interaction on human malaria parasite Plasmodium vivax in its natural/native vector Anopheles stephensi . Surprisingly we found that infectious blood meal lead to dramatic suppression in gut-bacteria population, a plausible strategy of P. vivax ookinetes to avoid immune responses. Our study suggests that for its own survival Plasmodium vivax causes early suppression of bacterial population, possibly by scavenging Fe from the blood meal which is indispensable for bacterial growth. Disruption and manipulation of this gut-microbe-interaction may help to design new ‘paratransgenesis’ molecular tool for malaria control.