Chalkophore mediated respiratory oxidase flexibility controls M. tuberculosis virulence

Oxidative phosphorylation has emerged as a critical therapeutic vulnerability of M. tuberculosis, but it is unknown how M. tuberculosis and other pathogens maintain respiration during infection. M. tuberculosis synthesizes diisonitrile lipopeptide chalkophores that chelate copper tightly, but their role in host-pathogen interactions is also unknown. We demonstrate that M. tuberculosis chalkophores maintain the function of the heme-copper bcc:aa3 respiratory oxidase under copper limitation. Chalkophore deficient M. tuberculosis cannot survive, respire to oxygen, or produce ATP under copper deprivation in culture. M. tuberculosis lacking chalkophore biosynthesis is attenuated in mice, a phenotype that is severely exacerbated by loss of the CytBD alternative respiratory oxidase (encoded by cydAB), revealing a multilayered flexibility of the respiratory chain that maintains oxidative phosphorylation during infection. Taken together, these data demonstrate that chalkophores counter host inflicted copper deprivation and highlight that protection of cellular respiration is a critical virulence function in M. tuberculosis.

Promoting Science Literacy and Awareness across the Globe: the Role of Scientists as Science Ambassadors

Science literacy has many personal and societal benefits that allows for better informed decision-making. Although the importance of science literacy is recognized globally, there are many challenges associated with its promotion. Scientists are more frequently engaging with nonscientific audiences through public outreach activities and with increasing support from institutions and professional societies. This is especially true regarding microbiologists and other related professionals since the start of the global 2019 coronavirus disease pandemic heightened the need to convey novel and rapidly evolving scientific information to lay audiences. The means by which professionals engage with these audiences affect the efficacy of the relay of scientific information. One method of engagement is the "ambassador approach," which aims to establish dialogue among different groups of people and scientists. In this perspective article, we discuss this approach, highlighting activities for the promotion of science literacy organized by the American Society for Microbiology Ambassador Program and similar programs of other scientific societies. We discuss the benefits and challenges of implementing an ambassador approach, propose potential improvements that could be made to existing programs promoting science literacy, and ultimately advocate for increased implementation of science ambassador programs.

Drosophila melanogaster Imd signaling interacts with insulin signaling and alters feeding rate upon parasitic nematode infection

Significant progress has been made in recent years on exploring immunometabolism, a field that integrates two processes essential for maintaining tissue and organismal homeostasis, immunity and metabolism. The nematode parasite Heterorhabditis gerrardi, its mutualistic bacteria Photorhabdus asymbiotica, and the fruit fly Drosophila melanogaster constitute a unique system to investigate the molecular basis of host immunometabolic response to nematode-bacterial complexes. In this study, we explored the contribution of the two major immune signaling pathways, Toll and Imd, to sugar metabolism in D. melanogaster larvae during infection with H. gerrardi nematodes. We infected Toll or Imd signaling loss-of-function mutant larvae with H. gerrardi nematodes and assessed larval survival ability, feeding rate, and sugar metabolism. We found no significant differences in the survival ability or levels of sugar metabolites in any of the mutant larvae when responding to H. gerrardi infection. However, we found that the Imd mutant larvae have higher feeding rate than controls during the early stages of infection. In addition, feeding rates are lower in Imd mutants relative to the control larvae as the infection progresses. We further showed that Dilp2 and Dilp3 gene expression increases in Imd mutants compared to controls early in the infection, but their expression levels decrease at later times. These findings indicate that Imd signaling activity regulates the feeding rate and Dilp2 and Dilp3 expression in D. melanogaster larvae infected with H. gerrardi. Results from this study facilitate our understanding of the link between host innate immunity and sugar metabolism in the context of infectious diseases caused by parasitic nematodes.

Activin and BMP Signaling Activity Affects Different Aspects of Host Anti-Nematode Immunity in Drosophila melanogaster

The multifaceted functions ranging from cellular and developmental mechanisms to inflammation and immunity have rendered TGF-ß signaling pathways as critical regulators of conserved biological processes. Recent studies have indicated that this evolutionary conserved signaling pathway among metazoans contributes to the Drosophila melanogaster anti-nematode immune response. However, functional characterization of the interaction between TGF-ß signaling activity and the mechanisms activated by the D. melanogaster immune response against parasitic nematode infection remains unexplored. Also, it is essential to evaluate the precise effect of entomopathogenic nematode parasites on the host immune system by separating them from their mutualistic bacteria. Here, we investigated the participation of the TGF-ß signaling branches, activin and bone morphogenetic protein (BMP), to host immune function against axenic or symbiotic Heterorhabditis bacteriophora nematodes (parasites lacking or containing their mutualistic bacteria, respectively). Using D. melanogaster larvae carrying mutations in the genes coding for the TGF-ß extracellular ligands Daw and Dpp, we analyzed the changes in survival ability, cellular immune response, and phenoloxidase (PO) activity during nematode infection. We show that infection with axenic H. bacteriophora decreases the mortality rate of dpp mutants, but not daw mutants. Following axenic or symbiotic H. bacteriophora infection, both daw and dpp mutants contain only plasmatocytes. We further detect higher levels of Dual oxidase gene expression in dpp mutants upon infection with axenic nematodes and Diptericin and Cecropin gene expression in daw mutants upon infection with symbiotic nematodes compared to controls. Finally, following symbiotic H. bacteriophora infection, daw mutants have higher PO activity relative to controls. Together, our findings reveal that while D. melanogaster Dpp/BMP signaling activity modulates the DUOX/ROS response to axenic H. bacteriophora infection, Daw/activin signaling activity modulates the antimicrobial peptide and melanization responses to axenic H. bacteriophora infection. Results from this study expand our current understanding of the molecular and mechanistic interplay between nematode parasites and the host immune system, and the involvement of TGF-ß signaling branches in this process. Such findings will provide valuable insight on the evolution of the immune role of TGF-ß signaling, which could lead to the development of novel strategies for the effective management of human parasitic nematodes.

Nematode infection and antinematode immunity in Drosophila

The entomopathogenic nematodes Heterorhabditis and Steinernema form mutualistic complexes with Gram-negative bacteria. These insect parasites have emerged as excellent research tools for studying nematode pathogenicity and elucidating the features that allow them to persist and multiply within the host. A better understanding of the molecular mechanisms of nematode infection and host antinematode processes will lead to the development of novel means for parasitic nematode control. Recent work has demonstrated the power of using the Drosophila infection model to identify novel parasitic nematode infection factors and elucidate the genetic and functional bases of host antinematode defense. Here, we aim to highlight the recent advances and address their contribution to the development of novel means for parasitic nematode control.

Immune interactions between Drosophila and the pathogen Xenorhabdus

Deciphering host innate immune function and bacterial pathogenic tactics require a system that facilitates both facets of host-pathogen interactions. In recent years, a model that becomes established in dissecting mechanisms of host antibacterial immune response through probing with a potent bacterial pathogen involves the fruit fly Drosophila melanogaster and the insect pathogenic bacteria Xenorhabdus spp. The elegance of this system involves not only the genetic tractability of D. melanogaster, but also the association of Xenorhabdus with parasitic nematodes of insects that supervise the release of the bacteria as well as influence their pathogenic properties during the infection process. These dynamic aspects have enabled us to start decoding the specific features of the D. melanogaster host defense that participate in confronting the activity of Xenorhabdus molecular components, which are designed to evade the immune system. Here we outline recent information on the cellular, humoral and phenoloxidase reactions that are induced in D. melanogaster larvae and adults to oppose the Xenorhabdus attack, and the bacterial factors responsible for triggering these effects. This knowledge is critical not only for understanding how invertebrate immunity operates, but also for devising novel approaches to exploit the virulence ability of certain bacteria with the ultimate goal to counteract harmful insect pests or vectors of infectious disease.

TGF-β Signaling Interferes With the Drosophila Innate Immune and Metabolic Response to Parasitic Nematode Infection

The common fruit fly, Drosophila melanogaster, is an outstanding model to study the molecular basis of anti-pathogen immunity. The parasitic nematode Heterorhabditis gerrardi, together with its mutualistic bacteria Photorhabdus asymbiotica, infects a wide range of insects, including D. melanogaster. Recently, we have shown that transforming growth factor-β (TGF-ß) signaling in D. melanogaster is regulated in response to parasitic nematode infection. In the current study, we investigated the contribution of two TGF-ß signaling branches, the activin and the bone morphogenetic protein (BMP), to D. melanogaster immune function against H. gerrardi. We used D. melanogaster larvae carrying mutations in the genes coding for the TGF-ß extracellular ligands daw and dpp. We have demonstrated that the number of circulating hemocytes in uninfected daw and dpp mutants decreases twofold compared to background controls, yet no significant changes in hemocyte numbers and survival of the TGF-ß mutants are observed upon nematode infection. However, we have shown that nematode-infected daw mutants express Dual oxidase at higher levels and phenoloxidase activity at lower levels compared to their background controls. To elucidate the contribution of TGF-ß signaling in the metabolic response of D. melanogaster to parasitic nematodes, we estimated lipid and carbohydrate levels in daw and dpp mutant larvae infected with H. gerrardi. We have found that both nematode-infected mutants contain lipid droplets of larger size, with daw mutant larvae also containing elevated glycogen levels. Overall, our findings indicate that the regulation of activin and BMP branches of TGF-ß signaling can alter the immune and metabolic processes in D. melanogaster during response to parasitic nematode infection. Results from this study shed light on the molecular signaling pathways insects activate to regulate mechanisms for fighting potent nematode parasites, which could lead to the identification of novel management strategies for the control of damaging pests.

Transcript analysis reveals the involvement of NF-κB transcription factors for the activation of TGF-β signaling in nematode-infected Drosophila

The common fruit fly Drosophila melanogaster is a powerful model for studying signaling pathway regulation. Conserved signaling pathways underlying physiological processes signify evolutionary relationship between organisms and the nature of the mechanisms they control. This study explores the cross-talk between the well-characterized nuclear factor kappa B (NF-κB) innate immune signaling pathways and transforming growth factor beta (TGF-β) signaling pathway in response to parasitic nematode infection in Drosophila. To understand the link between signaling pathways, we followed on our previous studies by performing a transcript-level analysis of different TGF-β signaling components following infection of immune-compromised Drosophila adult flies with the nematode parasites Heterorhabditis gerrardi and H. bacteriophora. Our findings demonstrate the requirement of NF-κB transcription factors for activation of TGF-β signaling pathway in Drosophila in the context of parasitic nematode infection. We observe significant decrease in transcript level of glass bottom boat (gbb) and screw (scw), components of the bone morphogenic protein (BMP) branch, as well as Activinβ (actβ) which is a component of the Activin branch of the TGF-β signaling pathway. These results are observed only in H. gerrardi nematode-infected flies compared to uninfected control. Also, this significant decrease in transcript level is found only for extracellular ligands. Future research examining the mechanisms regulating the interaction of these signaling pathways could provide further insight into Drosophila anti-nematode immune function against infection with potent parasitic nematodes.

Pre-exposure to non-pathogenic bacteria does not protect Drosophila against the entomopathogenic bacterium Photorhabdus

Immune priming in insects involves an initial challenge with a non-pathogenic microbe or exposure to a low dose of pathogenic microorganisms, which provides a certain degree of protection against a subsequent pathogenic infection. The protective effect of insect immune priming has been linked to the activation of humoral or cellular features of the innate immune response during the preliminary challenge, and these effects might last long enough to promote the survival of the infected animal. The fruit fly Drosophila melanogaster is a superb model to dissect immune priming processes in insects due to the availability of molecular and genetic tools, and the comprehensive understanding of the innate immune response in this organism. Previous investigations have indicated that the D. melanogaster immune system can be primed efficiently. Here we have extended these studies by examining the result of immune priming against two potent entomopathogenic bacteria, Photorhabdus luminescens and P. asymbiotica. We have found that rearing D. melanogaster on diet containing a non-pathogenic strain of Escherichia coli alone or in combination with Micrococcus luteus upregulates the antibacterial peptide immune response in young adult flies, but it does not prolong fly life span. Also, subsequent intrathoracic injection with P. luminescens or P. asymbiotica triggers the Immune deficiency and Toll signaling pathways in flies previously exposed to a live or heat-killed mix of the non-pathogenic bacteria, but the immune activation fails to promote fly survival against the pathogens. These findings suggest that immune priming in D. melanogaster, and probably in other insects, is determined by the type of microbes involved as well as the mode of microbial exposure, and possibly requires a comprehensive and precise alteration of immune signaling and function to provide efficient protection against pathogenic infection.

Dicer-2 Regulates Resistance and Maintains Homeostasis against Zika Virus Infection in Drosophila

Zika virus (ZIKV) outbreaks pose a massive public health threat in several countries. We have developed an in vivo model to investigate the host-ZIKV interaction in Drosophila We have found that a strain of ZIKV replicates in wild-type flies without reducing their survival ability. We have shown that ZIKV infection triggers RNA interference and that mutating Dicer-2 results in enhanced ZIKV load and increased susceptibility to ZIKV infection. Using a flavivirus-specific Ab, we have found that ZIKV is localized in the gut and fat body cells of the infected wild-type flies and results in their perturbed homeostasis. In addition, Dicer-2 mutants display severely reduced insulin activity, which could contribute toward the increased mortality of these flies. Our work establishes the suitability of Drosophila as the model system to study host-ZIKV dynamics, which is expected to greatly advance our understanding of the molecular and physiological processes that determine the outcome of this disease.

Role of Endosymbionts in Insect-Parasitic Nematode Interactions

Endosymbiotic bacteria exist in many animals where they develop relationships that affect certain physiological processes in the host. Insects and their nematode parasites form great models for understanding the genetic and molecular basis of immune and parasitic processes. Both organisms contain endosymbionts that possess the ability to interfere with certain mechanisms of immune function and pathogenicity. This review summarizes recent information on the involvement of insect endosymbionts in the response to parasitic nematode infections, and the influence of nematode endosymbionts on specific aspects of the insect immune system. Analyzing this information will be particularly useful for devising endosymbiont-based strategies to intervene in insect immunity or nematode parasitism for the efficient management of noxious insects in the field.