A morphological and molecular reinvestigation of Janickina pigmentifera (Grassi, 1881) Chatton 1953 – an amoebozoan parasite of arrow-worms (Chaetognatha)

Amoebozoan parasites of arrow-worms (Chaetognatha) were isolated from their hosts living in plankton of the Bay of Villefranche (Mediterranean Sea). Based on the light microscopic characters, the amoebae were identified as Janickina pigmentifera (Grassi, 1881) by their limax locomotive form and due to the presence of the intracellular symbiont, Perkinsela amoebae, surrounded by a layer of pigment granules. Sequences of the 18S rRNA gene of both J. pigmentifera and its symbiont were obtained for the first time. The molecular phylogenetic analyses of 18S rRNA gene placed J. pigmentifera within the genus Neoparamoeba, a taxon also characterized by the presence of a symbiont, known as Perkinsela amoebae-like organism (PLO). The 18S rRNA gene sequence of P. amoebae from J. pigmentifera grouped with the sequences of 18S rRNA genes of PLOs from Neoparamoeba branchiphila and Neoparamoeba invadens. The first photo documentation of the light microscopic features of J. pigmentifera, such as locomotive form, the morphology of the nucleus and P. amoebae have been provided. The new results support the affinity of J. pigmentifera with the family Paramoebidae suggested previously based on the presence of PLO. In contrast to Janickina, typical members of Paramoebidae (Neoparamoeba and Paramoeba) have a flattened, dactylopodial locomotive form. This discrepancy in morphology can be explained by the obligate parasitic lifestyle of Janickina.

Insect-host control of obligate, intracellular symbiont density

Many insects rely on intracellular bacterial symbionts to supplement their specialized diets with micronutrients. Using data from diverse and well-studied insect systems, we propose three lines of evidence suggesting that hosts have tight control over the density of their obligate, intracellular bacterial partners. First, empirical studies have demonstrated that the within-host symbiont density varies depending on the nutritional and developmental requirements of the host. Second, symbiont genomes are highly reduced and have limited capacity for self-replication or transcriptional regulation. Third, several mechanisms exist for hosts to tolerate, regulate and remove symbionts including physical compartmentalization and autophagy. We then consider whether such regulation is adaptive, by discussing the relationship between symbiont density and host fitness. We discuss current limitations of empirical studies for exploring fitness effects in host–symbiont relationships, and emphasize the potential for using mathematical models to formalize evolutionary hypotheses and to generate testable predictions for future work.

Influential Insider: Wolbachia, an Intracellular Symbiont, Manipulates Bacterial Diversity in Its Insect Host

Facultative intracellular symbionts like the α-proteobacteria Wolbachia influence their insect host phenotype but little is known about how much they affect their host microbiota. Here, we quantified the impact of Wolbachia infection on the bacterial community of the cabbage root fly Delia radicum by comparing the microbiota of Wolbachia-free and infected adult flies of both sexes. We used high-throughput DNA sequencing (Illumina MiSeq, 16S rRNA, V5-V7 region) and performed a community and a network analysis. In both sexes, Wolbachia infection significantly decreased the diversity of D. radicum bacterial communities and modified their structure and composition by reducing abundance in some taxa but increasing it in others. Infection by Wolbachia was negatively correlated to 8 bacteria genera (Erwinia was the most impacted), and positively correlated to Providencia and Serratia. We suggest that Wolbachia might antagonize Erwinia for being entomopathogenic (and potentially intracellular), but would favor Providencia and Serratia because they might protect the host against chemical plant defenses. Although they might seem prisoners in a cell, endocellular symbionts can impact the whole microbiota of their host, hence its extended phenotype, which provides them with a way to interact with the outside world.

Newly introduced Cardinium endosymbiont reduces microbial diversity in the rice brown planthopper Nilaparvata lugens

ABSTRACT Symbiotic microorganisms in invertebrates play vital roles in host ecology and evolution. Cardinium, a common intracellular symbiont, is transinfected into the important agricultural pest Nilaparvata lugens (rice brown planthopper) to regulate its reproduction, but how this impacts its microbial community is unknown. Here, we characterized the bacterial microbiota from N. lugens, with or without Cardinium, at different developmental stages and in various adult tissues using 16S ribosomal ribonucleic acid (16S rRNA) gene sequencing. Upon infection with Cardinium, we found that microbial diversity in the different developmental stages of N. lugens (especially females), and in female midguts and male testes, was lower than that in the uninfected control. There was a negative correlation between Cardinium and most related genera and between Bacteroidetes and Proteobacteria. Although the microbial structure varied during Cardinium infection, Acinetobacter spp. were a core microbiome genus. The Cardinium infection enhanced the relative density of midgut-associated Acinetobacter spp., with both bacteria exhibiting tissue-specific tropism. In addition, this infection caused the changes of main microbial functions in N. lugens. These results offer insights into the effects of alien (i.e. newly introduced from other organism) Cardinium infection on N. lugens-associated microbiotas, aiding in the development of transinfected endosymbionts for pest control.

The Intracellular Symbiont Wolbachia pipientis Enhances Recombination in a Dose-Dependent Manner

Wolbachia pipientis is an intracellular alphaproteobacterium that infects 40%–60% of insect species and is well known for host reproductive manipulations. Although Wolbachia are primarily maternally transmitted, evidence of horizontal transmission can be found in incongruent host–symbiont phylogenies and recent acquisitions of the same Wolbachia strain by distantly related species. Parasitoids and predator–prey interactions may indeed facilitate the transfer of Wolbachia between insect lineages, but it is likely that Wolbachia are acquired via introgression in many cases. Many hypotheses exist to explain Wolbachia prevalence and penetrance, such as nutritional supplementation, protection from parasites, protection from viruses, or direct reproductive parasitism. Using classical genetics, we show that Wolbachia increase recombination in infected lineages across two genomic intervals. This increase in recombination is titer-dependent as the wMelPop variant, which infects at higher load in Drosophila melanogaster, increases recombination 5% more than the wMel variant. In addition, we also show that Spiroplasma poulsonii, another bacterial intracellular symbiont of D. melanogaster, does not induce an increase in recombination. Our results suggest that Wolbachia infection specifically alters its host’s recombination landscape in a dose-dependent manner.

Host-Microbe Interactions in the Chemosynthetic Riftia pachyptila Symbiosis

ABSTRACT The deep-sea tubeworm Riftia pachyptila lacks a digestive system but completely relies on bacterial endosymbionts for nutrition. Although the symbiont has been studied in detail on the molecular level, such analyses were unavailable for the animal host, because sequence information was lacking. To identify host-symbiont interaction mechanisms, we therefore sequenced the Riftia transcriptome, which served as a basis for comparative metaproteomic analyses of symbiont-containing versus symbiont-free tissues, both under energy-rich and energy-limited conditions. Our results suggest that metabolic interactions include nutrient allocation from symbiont to host by symbiont digestion and substrate transfer to the symbiont by abundant host proteins. We furthermore propose that Riftia maintains its symbiont by protecting the bacteria from oxidative damage while also exerting symbiont population control. Eukaryote-like symbiont proteins might facilitate intracellular symbiont persistence. Energy limitation apparently leads to reduced symbiont biomass and increased symbiont digestion. Our study provides unprecedented insights into host-microbe interactions that shape this highly efficient symbiosis. IMPORTANCE All animals are associated with microorganisms; hence, host-microbe interactions are of fundamental importance for life on earth. However, we know little about the molecular basis of these interactions. Therefore, we studied the deep-sea Riftia pachyptila symbiosis, a model association in which the tubeworm host is associated with only one phylotype of endosymbiotic bacteria and completely depends on this sulfur-oxidizing symbiont for nutrition. Using a metaproteomics approach, we identified both metabolic interaction processes, such as substrate transfer between the two partners, and interactions that serve to maintain the symbiotic balance, e.g., host efforts to control the symbiont population or symbiont strategies to modulate these host efforts. We suggest that these interactions are essential principles of mutualistic animal-microbe associations.

The Jekyll and Hyde Symbiont: Could Wolbachia Be a Nutritional Mutualist?

ABSTRACT The most common intracellular symbiont on the planet—Wolbachia pipientis—is infamous largely for the reproductive manipulations induced in its host. However, more recent evidence suggests that this bacterium may also serve as a nutritional mutualist in certain host backgrounds and for certain metabolites. We performed a large-scale analysis of conserved gene content across all sequenced Wolbachia genomes to infer potential nutrients made by these symbionts. We review and critically evaluate the prior research supporting a beneficial role for Wolbachia and suggest future experiments to test hypotheses of metabolic provisioning.

Wolbachia Infection in Two Species: Novel Views on the Colonization Ability of Wolbachia in Aphids

Wolbachia pipientis (Rickettsiales: Anaplasmataceae) is an intracellular symbiont residing in arthropods and filarial nematodes. Sixteen supergroups have been described from different host taxa. Four supergroups A, B, M, and N were found in aphids according to prior studies. The cotton aphid, Aphis gossypii, and the green peach aphid, Myzus persicae, are typical polyphagous species with global distributions. We conducted an extensive and systematic survey of Wolbachia infections in these aphids from China. High incidences of Wolbachia infection were detected. The total infection incidence was 60% in A. gossypii and 88% in M. persicae. Both aphid species were infected with supergroups A, B and M. Different incidences of infection were observed among the seven geographical regions in China, which suggested a positive relationship between Wolbachia infections and the geographical distribution of aphid species. Furthermore, multiple infection patterns (M, B, A&M, B&M, and A&B&M) were observed. Infection patterns M and B&M were detected in almost all populations. Patterns A&B&M and B showed geographical restriction in North China. Three factors can possibly influence the Wolbachia infection incidences and patterns: the geographical distribution, aphid species, and different supergroup types.

Trading amino acids at the aphid–Buchnera symbiotic interface

Plant sap-feeding insects are widespread, having evolved to occupy diverse environmental niches despite exclusive feeding on an impoverished diet lacking in essential amino acids and vitamins. Success depends exquisitely on their symbiotic relationships with microbial symbionts housed within specialized eukaryotic bacteriocyte cells. Each bacteriocyte is packed with symbionts that are individually surrounded by a host-derived symbiosomal membrane representing the absolute host–symbiont interface. The symbiosomal membrane must be a dynamic and selectively permeable structure to enable bidirectional and differential movement of essential nutrients, metabolites, and biosynthetic intermediates, vital for growth and survival of host and symbiont. However, despite this crucial role, the molecular basis of membrane transport across the symbiosomal membrane remains unresolved in all bacteriocyte-containing insects. A transport protein was immunolocalized to the symbiosomal membrane separating the pea aphid Acyrthosiphon pisum from its intracellular symbiont Buchnera aphidicola. The transporter, A. pisum nonessential amino acid transporter 1, or ApNEAAT1 (gene: ACYPI008971), was characterized functionally following heterologous expression in Xenopus oocytes, and mediates both inward and outward transport of small dipolar amino acids (serine, proline, cysteine, alanine, glycine). Electroneutral ApNEAAT1 transport is driven by amino acid concentration gradients and is not coupled to transmembrane ion gradients. Previous metabolite profiling of hemolymph and bacteriocyte, alongside metabolic pathway analysis in host and symbiont, enable prediction of a physiological role for ApNEAAT1 in bidirectional host–symbiont amino acid transfer, supplying both host and symbiont with indispensable nutrients and biosynthetic precursors to facilitate metabolic complementarity.

The intracellular symbiont Wolbachia enhances recombination in a dose-dependent manner

Wolbachia pipientis is an intracellular alphaproteobacterium that infects 40-60% of insect species and is well known for host reproductive manipulations. Although Wolbachia are primarily maternally transmitted, evidence of horizontal transmission can be found in incongruent host-symbiont phylogenies and recent acquisitions of the same Wolbachia strain by distantly related species. Parasitoids and predator-prey interactions may indeed facilitate the transfer of Wolbachia between insect lineages but it is likely that Wolbachia are acquired via introgression in many cases. Many hypotheses exist as to explain Wolbachia prevalence and penetrance such as nutritional supplementation, protection from parasites, protection from viruses, or straight up reproductive parasitism. Using classical genetics we show that Wolbachia increase recombination in infected lineages across two genomic intervals. This increase in recombination is titer dependent as the wMelPop variant, which infects at higher load in Drosophila melanogaster, increases recombination 5% more than the wMel variant. In addition, we also show that Spiroplasma poulsonii, the other bacterial intracellular symbiont of Drosophila melanogaster, does not induce an increase in recombination. Our results suggest that Wolbachia infection specifically alters host recombination landscape in a dose dependent manner.Article SummaryThe ubiquitous bacterial symbiont Wolbachia is known to alter host reproduction through manipulation of host cell biology, protect from pathogens, and supplement host nutrition. In this work we show that Wolbachia specifically increases host recombination in a dose dependent manner. Flies harboring Wolbachia exhibit elevated rates of recombination across the 2nd and X chromosomes and this increase is proportional to their Wolbachia load. In contrast, another intracellular symbiont, Spiroplasma, does not lead to an increase in recombination across the intervals tested. Our results point to a specific effect of Wolbachia infection that may have a significant effect on infected insect populations.