Wolbachia Interferes with Ferritin Expression and Iron Metabolism in Insects

et al. (2009) Wolbachia Interferes with Ferritin Expression and Iron Metabolism in Insects. PLoS Pathog 5(10): e1000630. doi:10.1371/journal.ppat.1000630 Wolbachia Interferes with Ferritin Expression and Iron Metabolism in Insects Natacha Kremer 0 Denis Voronin 0 Delphine Charif 0 Patrick Mavingui 0 Bertrand Mollereau 0 Fabrice 0 David S. Schneider, Stanford University, United States of America 0 1 Universite de Lyon, Lyon; Universite Lyon 1; CNRS, UMR 5558, Laboratoire de Biome trie et Biologie Evolutive, Villeurbanne, France, 2 Universite de Lyon, Lyon; Universite Lyon 1; CNRS, UMR 5557, Laboratoire d'Ecologie Microbienne , Villeurbanne, France, 3 LBMC , UMR5239 CNRS/Ecole Normale Supe rieure de Lyon, IFR 128 Biosciences Lyon Gerland, Universite de Lyon , Lyon , France Wolbachia is an intracellular bacterium generally described as being a facultative reproductive parasite. However, Wolbachia is necessary for oogenesis completion in the wasp Asobara tabida. This dependence has evolved recently as a result of interference with apoptosis during oogenesis. Through comparative transcriptomics between symbiotic and aposymbiotic individuals, we observed a differential expression of ferritin, which forms a complex involved in iron storage. Iron is an essential element that is in limited supply in the cell. However, it is also a highly toxic precursor of Reactive Oxygen Species (ROS). Ferritin has also been shown to play a key role in host-pathogen interactions. Measuring ferritin by quantitative RTPCR, we confirmed that ferritin was upregulated in aposymbiotic compared to symbiotic individuals. Manipulating the iron content in the diet, we showed that iron overload markedly affected wasp development and induced apoptotic processes during oogenesis in A. tabida, suggesting that the regulation of iron homeostasis may also be related to the obligate dependence of the wasp. Finally, we demonstrated that iron metabolism is influenced by the presence of Wolbachia not only in the obligate mutualism with A. tabida, but also in facultative parasitism involving Drosophila simulans and in Aedes aegypti cells. In these latter cases, the expression of Wolbachia bacterioferritin was also increased in the presence of iron, showing that Wolbachia responds to the concentration of iron. Our results indicate that Wolbachia may generally interfere with iron metabolism. The high affinity of Wolbachia for iron might be due to physiological requirement of the bacterium, but it could also be what allows the symbiont to persist in the organism by reducing the labile iron concentration, thus protecting the cell from oxidative stress and apoptosis. These findings also reinforce the idea that pathogenic, parasitic and mutualistic intracellular bacteria all use the same molecular mechanisms to survive and replicate within host cells. By impacting the general physiology of the host, the presence of a symbiont may select for host compensatory mechanisms, which extends the possible consequences of persistent endosymbiont on the evolution of their hosts. - Funding: This work was supported by a grant of the Agence Nationale de la Recherche (ANR-06-BLANC-0316 EndoSymbArt) and by a grant of the Fondation Innovations en Infectiologie (FINOVI 005). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Symbiotic interactions, in which long-term interactions take place between two partners belonging to different species, are common in nature [1]. These associations form a continuum ranging from parasitism to mutualism with respect to the outcome of the association (i.e. the cost or benefit for the host), and can be either facultative or obligate for the host. It has usually been assumed that parasitic, commensal or mutualistic symbionts interact in fundamentally different ways with their host. However, many bacterial symbionts can exist either as a mutualist or as a parasite, depending on their host [2,3]. In addition, increasing reports in the literature indicate that the same molecular mechanisms are used by both parasitic and mutualistic symbionts to interact with their host [4]. If we focus on endocytobionts (i.e. symbionts living within the cells of their hosts), several mechanisms are known to be shared by parasites and mutualists, such as recognition and specific binding to the host cell, internalization within the cell, and finally intracellular survival and growth [5]. Common molecular mechanisms have been identified which are related to (i) communication processes, such as symbiosis/ virulence factors that encode genes classically involved in secretion systems [6] (ii) survival and replication processes, including the expression of colonization factors [7], evading host immune systems [8], and regulating bacterial growth, and (iii) physiological processes involved in environmental adaptation, such as pH modification, induction of specific metabolic pathways, development of iron uptake strategies [9] and induction of stress proteins [10]. In this paper, we focus on Wolbachia (Rickettsiales), a well-known genus of bacteria that are reproductive parasites when associated with arthropod hosts [11] but mutualists when associated with nematodes [12]. Unlike other Wolbachia strains, which are generally facultative for their arthropods host, Wolbachia is necessary for oogenesis to be completed in the parasitoid wasp Asobara tabida (Hymenoptera, Braconidae) [13]. Wolbachia does not Wolbachia are intracellular bacteria that infect numerous invertebrate species, where they are generally facultative for their host. Surprisingly, the wasp Asobara tabida is dependent on Wolbachia for egg production: in uninfected females, the cells necessary for egg maturation die prematurely as a result of apoptosis. When we analyzed the genetic basis of this dependence, we found that ferritin, a protein involved in the regulation of iron homeostasis, was over-expressed in uninfected individuals. We also found that Wolbachia interferes with iron metabolism and ferritin expression in other hostWolbachia associations. Furthermore, Wolbachia itself responds to changes in iron concentration by changing the expression of bacterioferritin. Iron is in short supply within the cell, and is necessary for both host and symbiont; our findings highlight the key role of iron in hostsymbiont interactions, as had previously been shown for host pathogen interactions. Furthermore, iron homeostasis is involved in the regulation of oxidative stress, which in turn is involved in inducing cell death. Wolbachia could also interfere with iron in a way that limits oxidative stress and cell death, thus promoting its persistence within host cells. In A. tabida, we show that iron induced cell death in the ovaries, suggesting that iron metabolism could also be linked to the evolution of depend (...truncated)