Biology subjects

Hypsa, V.

Publications and source records attributed to Hypsa, V..

17 recordsLinked to original sources

bioRxiv2026

Caught in transition: facultative intracellularity and genome evolution of Symbiopectobacterium in Rhodnius species

Blood-feeding insects typically depend on obligate intracellular bacterial symbionts that provide essential B vitamins absent from vertebrate blood. In contrast, kissing bugs (Triatominae) have long been considered atypical because they rely primarily on extracellular gut-associated bacteria. Recent reports of the genus Symbiopectobacterium in Rhodnius species raise questions about the diversity and evolution of symbiosis in these insects. Here, we investigate the distribution, genome evolution, and tissue localization of Symbiopectobacterium in the genus Rhodnius. Using comparative metagenomics, phylogenomics, fluorescence in situ hybridization, transmission electron microscopy, and hemolymph screening, we characterize a Symbiopectobacterium genome from Rhodnius prolixus and assess its occurrence across publicly available datasets representing multiple Rhodnius species. The R. prolixus strain possesses a large, highly dynamic genome enriched in mobile genetic elements, pseudogenes, and remnants of secretion systems, while retaining biosynthetic pathways for several B vitamins. Comparative analysis revealed variation in genome reduction among Rhodnius-associated strains, suggesting ongoing and potentially independent transitions toward host-restricted symbiosis. Localization analyses detected Symbiopectobacterium intracellularly within posterior midgut epithelial cells and occasionally in the hemolymph, consistent with a facultative intracellular lifestyle. However, no bacteriomes or stable intracellular structures were observed. Together, these findings indicate that Symbiopectobacterium represents an intermediate stage in the transition from environmentally associated bacteria to obligate intracellular mutualists in Triatominae.

microbiology↗

bioRxiv2026

Arsenophonus ghosts in bed bug genomes: multiple origins and 50 million years of persistence

Although numerous studies have documented horizontal gene transfer (HGT) from bacteria into insect genomes, they have been heavily biased toward the endosymbiont Wolbachia. In contrast, comparatively few studies have examined HGT from other symbionts and insect-associated bacteria. Moreover, research on these systems has primarily focused on transferred genes that retain function in the insect host, contributing to metabolism, symbiosis, detoxification, or host adaptation. Consequently, relatively few empirical systems have been available to investigate the persistence, degradation, diversification, and vertical inheritance of apparently non-functional HGT-derived sequences over macroevolutionary timescales. The widespread occurrence of putatively Arsenophonus-derived sequences across Cimicidae therefore provides a rare opportunity to extend these investigations beyond the Wolbachia model and to examine the long-term evolutionary fate of non-functional HGT-derived DNA across tens of millions of years of host diversification. We show that Arsenophonus-derived HGTs have multiple independent origins across Cimicidae but that one major HGT lineage has persisted through diversification of the subfamily Cimicinae for at least 50 million years. Phylogenetic and compositional analyses indicate that an ancestral Arsenophonus-derived genomic region has undergone progressive fragmentation, leaving numerous dispersed, apparently non-functional remnants while preserving a clear evolutionary signature. These results extend the study of bacterial HGT beyond the Wolbachia model and demonstrate that non-functional symbiont-derived DNA can persist over macroevolutionary timescales.

evolutionary biology↗

bioRxiv2025

Generalist vs specialist strategy shapes microbiomes in blood feeding parasite Polyplax serrata.

Insects live in association with bacterial communities, collectively referred to as the microbiome. Microbiome composition varies widely across insect taxa and is shaped by multiple factors, including host phylogeny, environmental conditions, geographic distribution, and nutritional ecology. One hypothesis is that microbiome composition may also reflect whether the host adopts a generalist or specialist ecological strategy. We tested this hypothesis using the sucking louse Polyplax serrata, which offers several advantages as a model system. First, as permanent ectoparasites, lice inhabit a relatively stable and simplified environment, thereby minimizing potential confounding variables. Second, within P. serrata, two closely related lineages have been identified: one restricted to a single rodent host (Apodemus flavicollis), and the other exploiting two hosts (A. flavicollis and A. sylvaticus). We analyzed and compared microbiome structure in these two lineages using 16S rRNA gene amplicon sequencing. While alpha diversity did not differ between the lineages, beta diversity differed significantly, particularly in pairwise dissimilarities among individual samples. These results suggest that in P. serrata, host specialization strategy influences microbiome diversity, with the "generalist" lineage harboring more heterogeneous communities. This finding extends previous observations on ecological divergence between the two lineages, showing that closely related cryptic species with highly similar genomes, living sympatrically in the same environment, can rapidly evolve distinct life strategies that, in turn, shape both their genetic structure and their microbiomes.

evolutionary biology↗

bioRxiv2025

Dynamic but constrained: Repeated acquisitions of nutritional symbionts in bed bugs (Heteroptera: Cimicidae) from a narrow taxonomic pool.

BackgroundBed bugs (Heteroptera: Cimicidae), like other strictly blood-feeding insects, harbor obligate bacterial symbionts that supply essential nutrients (especially B vitamins) lacking in their blood diet. The primary obligate symbionts are transovarially transmitted Wolbachia, notable for having horizontally acquired biotin operon. In addition to these symbionts with the confirmed nutritional role, bacteria from the genera Symbiopectobacterium and Tisiphia have also been found to be transovarially transmitted in bed bugs. Their significance to the host fitness remains unclear; they are considered facultative, and thus likely non-essential. However, this understanding of bed bugs symbiosis is based exclusively on studies of the human-associated common bed bug (Cimex lectularius) and few related Cimicinae species. Virtually nothing is known about the diversity, origins, or metabolic roles of symbionts across the more than hundred described bed bug species. ResultsUsing amplicon and metagenomic analyzes, we identified five different bacterial genera as potential bed bug symbionts: Wolbachia, Symbiopectobacterium, Sodalis, Serratia, and Tisiphia. The distribution of these bacteria among 13 bed bug species indicated at least 16 independent origins of symbiosis (some samples harboring multiple symbiont strains). A comparison of host and symbiont phylogenies suggested that some of these origins were followed by cospeciation. Not all bed bugs, however, harbored Wolbachia. In the subfamily Cacodminae, Symbiopectobacterium (previously known as facultative symbiont) was detected as the sole symbiont, suggesting its role as an essential, obligate symbiont. Analysis of 23 obtained genome drafts revealed considerable differences in their size and gene content, indicating that these bacteria have reached different stages in the evolution towards obligate symbiosis. As is common in symbiotic bacteria, the analyzed genomes have lost many biosynthetic capacities. A comparison of B-vitamin synthesis pathways showed that only two, riboflavin and lipoic acid, were preserved across all symbionts. ConclusionsAn overview of symbiosis across a broad phylogenetic span of bed bugs reveals that this insect family has undergone remarkably dynamic evolution, characterized by multiple independent symbiont acquisitions, episodes of cospeciations, and frequent co-occurrence of multiple symbionts within individual hosts. Interestingly, although these symbionts were acquired through multiple independent events, the majority belong to just three bacterial genera (Wolbachia, Symbiopectobacterium, and Sodalis), suggesting an unknown mechanisms underlying bed bug-symbiont specificity. Two aspects of this study warrant further investigation. First, the finding of Symbiopectobacterium as the sole obligate symbiont in Cacodminae suggests that expanding the taxonomic sampling may reveal an even more complex structure of symbiosis within bed bugs. Second, the inconsistencies and uncertainties in evaluating the functionality of the biotin synthesis indicate that further research will be necessary to better understand the evolution of this B vitamin pathway in symbiotic bacteria.

evolutionary biology↗

bioRxiv2024

An obligate symbiont of Haematomyzus elephantis with a strongly reduced genome resembles symbiotic bacteria in sucking lice

The parvorder Rhynchophthirina with a single genus Haematomyzus is a small group of ectoparasites related to sucking and chewing lice. Previous screening based on the 16S rRNA gene indicated that Haematomyzus harbour a symbiotic bacterium whose DNA exhibits a strong shift in nucleotide composition typical of obligate mutualistic symbionts in insects. Within Phthiraptera, the most dramatically reduced genomes are found in the symbionts associated with sucking lice, living exclusively on mammal blood, compared to the less modified symbionts inhabiting the chewing lice, which feed on skin derivates. In this study, we investigate the genome characteristics of the symbiont associated with Haematomyzus elephantis. We sequenced and assembled the Haematomyzus elephantis metagenome, extracted a genome draft of its symbiotic bacterium, and show that the symbiont has a significantly reduced genome, which is with 0.39 Mbp the smallest genome among the symbionts known from Phthiraptera. Multigenic phylogenetic analysis places the symbiont into one of three clusters composed of long-branched symbionts from other insects. More specifically, it clusters together with symbionts from several other sucking lice, and also with Wigglesworthia glossinidia, an obligate symbiont of tsetse flies. Consistent with the dramatic reduction of its genome, the H. elephantis symbiont lost many metabolic capacities. However, it retained functional pathways for four B vitamins, a trait typical for symbionts in blood-feeding insects. Considering genomic, metabolic, and phylogenetic characteristics, the new symbiont closely resembles those known from several sucking lice rather than chewing lice. ImportanceRhynchophthirina is a unique small group of permanent ectoparasites that is closely related to both sucking and chewing lice. These two groups of lice differ in their morphology, ecology, and feeding strategies. As a consequence of their different dietary sources, such as mammals blood versus vertebrate skin derivatives, they also exhibit distinct patterns of symbiosis with obligate bacterial symbionts. While Rhynchophthirina shares certain traits with sucking and chewing lice, the nature of its obligate symbiotic bacterium and its metabolic role are not known. In this study, we assemble genome of symbiotic bacterium from Haematomyzus elphantis (Rhynchophthirina), demonstrating its close similarity and phylogenetic proximity to several symbionts of sucking lice. The genome is highly reduced (representing the smallest genome among louse-associated symbionts) and exhibits a significant loss of metabolic pathways. However, similar to other louse symbionts, it retains essential pathways for the synthesis of several B vitamins.

genomics↗

bioRxiv2024

Fur microbiome as a putative source of symbiotic bacteria in sucking lice

Symbiosis between insects and bacteria has been established countless times. While it is well known that the symbionts originated from a variety of different bacterial taxa, it is usually difficult to determine their environmental source and a route of their acquisition by the host. In this study, we address this question using a model of Neisseriaceae symbionts in rodent lice. These bacteria established their symbiosis independently with different louse taxa (Polyplax, Hoplopleura, Neohaematopinus), most likely from the same environmental source. We first applied amplicon analysis to screen for candidate source bacterium in the louse environment, that is, three species of rodents (Microtus arvalis, Clethrionomys glareolus, and Apodemus flavicollis). The screened samples included rodent fur, skin, spleen, and ectoparasites sampled from the rodents. The amplicon analysis revealed a Neisseriaceae bacterium, closely related to the known louse symbionts. We assembled genome drafts of this environmental bacterium from all three rodent hosts. The sizes of the three drafts converged to a remarkably small size of approximately 1.4 Mbp, which is even smaller than the genomes of the related symbionts. Based on these findings, we propose a hypothetical scenario of the genome evolution during the transition of a free-living bacterium to the member of the rodent fur-associated microbiome and subsequently to the facultative and obligate louse symbionts.

ecology↗

bioRxiv2023

Highly resolved genomes as a tool for studying speciation history of two closely related louse lineages with different host specificities.

Sucking lice of the suborder Anoplura are permanent ectoparasites with specific lifestyle and highly derived features. Currently, genomic data are only available for a single species, the human louse Pediculus humanus. In this study we present genomes of two distinct lineages, with different host spectra, of a rodent louse Polyplax serrata. Genomes of these ecologically different lineages are closely similar in gene content, display a high level of synteny, but they also differ by a few duplications/translocations and single inversion. Compared to P. humanus, the two P. serrata genomes are noticeably larger (139 Mbp vs. 111 Mbp) and encode a higher number of genes. Similar to P. humanus, they are significantly reduced in sensory-related categories such as vision and olfaction. Utilizing a genome-wide set of genes, we perform phylogenetic reconstruction and evolutionary dating of the P. serrata lineages. Obtained estimates reveal their relatively deep origin (approx. 6.5 Mya), comparable to the time of split between the human and chimpanzee lice Pediculus humanus and P. schaeffi. This dating supports the view that the P. serrata lineages are likely to represent two cryptic species with different host spectra. Historical demographies of the two lineages show glaciation-related population size (Ne) reduction, but recent restoration of Ne was seen only in the less host specific lineage. Together with the louse genomes, we analyze genomes of their bacterial symbiont Legionella polyplacis, and evaluate their potential complementarity in synthesis of amino acids and B vitamins. We show that both systems, Polyplax/Legionella and Pediculus/Riesia, display almost identical patterns, with symbionts involved in synthesis of B vitamins but not amino acids.

genomics↗

bioRxiv2023

Arsenophonus symbiosis with louse flies: multiple origins, coevolutionary dynamics, and metabolic significance

Arsenophonus is a widespread insect symbiont with life strategies that vary from parasitism to obligate mutualism. In insects living exclusively on vertebrate blood, mutualistic Arsenophonus strains are presumed to provide B vitamins missing in the insect host diet. Hippoboscidae, obligate blood-feeders related to tsetse flies, were previously suggested to have acquired Arsenophonus symbionts in several independent events. Based on comparative genomic analyzes of eleven Hippoboscidae-associated strains, nine of them newly assembled, we reveal a wide range of their genomic characteristics and phylogenetic affiliations. Phylogenetic patterns and genomic traits split the strains into two different types. Seven strains display characteristics of obligate mutualists with significantly reduced genomes and long phylogenetic branches. The remaining four genomes cluster on short branches, and their genomes resemble those of free-living bacteria or facultative symbionts. Both phylogenetic positions and genomic traits indicate that evolutionary history of the Hippoboscidae-Arsenophonus associations is a mixture of short-term coevolutions with at least four independent origins. The comparative approach to a reconstruction of B vitamin pathways across the available Arsenophonus genomes produced two kinds of patterns. On one hand, it indicated the different importance of individual B vitamins in the host-symbiont interaction. While some (riboflavin, pantothenate, folate) seem to be synthesized by all Hippoboscidae-associated obligate symbionts, pathways for others (thiamine, nicotinamide, cobalamin) are mostly missing. On the other hand, the broad comparison produced patterns which can serve as bases for further assessments of the pathways completeness and functionality. ImportanceInsects that live exclusively on vertebrate blood utilize symbiotic bacteria as a source of essential compounds, e.g. B vitamins. In louse flies, the most frequent symbiont originated in genus Arsenophonus, known from a wide range of insects. Here, we analyze genomic traits, phylogenetic origins, and metabolic capacities of eleven Arsenophonus strains associated with louse flies. We show that in louse flies Arsenophonus established symbiosis in at least four independent events, reaching different stages of symbiogenesis. This allowed for comparative genomic analysis, including convergence of metabolic capacities. The significance of the results is two-fold. First, based on a comparison of independently originated Arsenophonus symbioses, it determines the importance of individual B vitamins for the insect host. This expands our theoretical insight into insect-bacteria symbiosis. The second outcome is of methodological significance. We show that the comparative approach reveals artifacts that would be difficult to identify based on a single-genome analysis.

evolutionary biology↗

bioRxiv2023

Genome dynamics across the evolutionary transition to endosymbiosis

Endosymbiosis - where a microbe lives and replicates within a host - is an important contributor to organismal function that has accelerated evolutionary innovations and catalysed the evolution of complex life. The evolutionary processes associated with transitions to endosymbiosis, however, are poorly understood. Here, we use comparative genomics of the genus Arsenophonus to reveal the complex processes that occur on evolution of an endosymbiotic lifestyle. We compared the genomes of 38 strains spanning diverse lifestyles from environmentally acquired infections to obligate inter-dependent endosymbionts. We observed recent endosymbionts had larger genome sizes than closely related environmentally acquired strains, consistent with evolutionary innovation and rapid gain of new function. Increased genome size was a consequence of prophage and plasmid acquisition including a cargo of type III effectors, and concomitant loss of CRISPR-Cas genome defence systems enabling mobile genetic element expansion. Persistent endosymbiosis was also associated with loss of type VI secretion, likely reflecting reduced microbe-microbe competition. Thereafter, the transition to stable endosymbiosis and vertical inheritance was associated with the expected relaxation of purifying selection, pseudogenisation of genes and reduction of metabolism, leading to genome reduction. However, reduced %GC that is typically considered a progressive linear process was observed only in obligate interdependent endosymbionts. We argue that a combination of the need for rapid horizontal gene transfer-mediated evolutionary innovation together with reduced phage predation in endosymbiotic niches drives loss of genome defence systems and rapid genome expansion upon adoption of endosymbiosis. These remodelling processes precede the reductive evolution traditionally associated with adaptation to endosymbiosis.

genomics↗

bioRxiv2021

Extremely reduced supergroup F Wolbachia: transition to obligate insect symbionts

Wolbachia are widely distributed symbionts among invertebrates that manifest by a broad spectrum of lifestyles from parasitism to mutualism. Wolbachia Supergroup F is considered a particularly interesting group which gave rise to symbionts of both arthropods and nematodes, and some of its members are obligate mutualists. Further investigations on evolutionary transitions in symbiosis have been hampered by a lack of genomic data for Supergroup F members. In this study, we present genomic data for five new supergroup F Wolbachia strains associated with four chewing lice species. These new strains in different evolutionary stages show genomic characteristics well-illustrating the evolutionary trajectory which symbiotic bacteria experience during their transition to mutualism. Three of the strains have not yet progressed with the transition, the other two show typical signs of ongoing gene deactivation and removal (genome size, coding density, low number of pseudogenes). Particularly, wMeur1, a symbiont fixed in all Menacanthus eurysternus populations across four continents, possesses a highly reduced genome of 733,850 bp with a horizontally acquired capacity for pantothenate synthesis. Comparing with other strains showed wMeur1 genome as the smallest currently known among all Wolbachia and the first example of Wolbachia which has completed genomic streamlining known from the gammaproteobacterial obligate symbionts.

evolutionary biology↗

bioRxiv2021

Development and validation of an LC-MS/MS method for determination of B vitamins and some its derivatives in whole blood

Obligate symbiotic bacteria associated with the insects feeding exclusively on vertebrate blood are supposed to complement B vitamins presumably lacking in their diet, vertebrate blood. Recent genomic analyses revealed considerable differences in biosynthetic capacities across different symbionts, indicating that levels of B vitamins vary across different vertebrate hosts. However, a rigorous determination of B vitamins content in blood of various vertebrates has not yet been approached. A reliable analytical method focused on B vitamin complex in blood and hemolymph can provide valuable informative background and understanding of general principles of insect symbiosis. In this work chromatographic separation of a mixture of eight B vitamins (B1 - thiamine, B2 - riboflavin, B3 - niacin, B5 - pantothenic acid, B6 - pyridoxine, B7 - biotin, B9 - folic acid and B12 - cyanocobalamine), four B vitamin derivatives (B3 - niacinamide, B6 - pyridoxal-5-phosphate, B6 - 4-pyridoxic acid and B9 - tetrahydrofolic acid) and 3 stable isotope labelled internal standards (B3 - niacin-13C6, B5 - pantothenic acid (di-{beta}-alanine-13C6,15N2) and B7 - biotin-(ring-6,6-d2)) on C30 column was developed. Detection was carried out using dual-pressure linear ion trap mass spectrometer in FullScan MS/MS and SIM mode. Matching internal standards with analytes was done according to the results of linearity, accuracy and precision. Except for vitamin B9 (tetrahydrofolic acid) instrument quantitation limits of all analytes were ranging from 0.42 to 5.0 g/L, correlation coefficients from 0.9997 to 1.0000 and QC coefficients from 0.53 to 3.2 %. Optimization of whole blood sample preparation step was focused especially on evaluation of two types of protein-precipitation agents: trichloroacetic acid and zinc sulphate in methanol. Samples of whole blood prepared in six independent replicates were spiked at 10 g/L and 100 g/L level. The best results were obtained for zinc sulphate in methanol, but only nine analytes (B1 - thiamine, B2 - riboflavin, B3 - niacin, B3 - niacinamide, B5 - pantothenic acid, B6 - pyridoxine, B6 - 4-pyridoxic acid, B7 - biotin and B12 - cyanocobalamine) were successfully validated. Accuracy of the procedure using this protein-precipitating agent was ranging from 89 to 120 %, precision from 0.5 to 13 % and process efficiency from 65 to 108 %. HighlightsO_LILC-MS/MS method for quantitation of eight B vitamins and four B vitamin derivatives was developed. C_LIO_LIDeproteinization agents trichloroacetic acid and ZnSO4/methanol were tested for protein precipitation of whole blood. C_LIO_LIAccuracy, precision and process efficiency were evaluated. C_LIO_LISuccessful method validation for seven B vitamins and two B vitamin derivatives in whole blood. C_LI

biochemistry↗

bioRxiv2020

Ontogeny, species identity and environment dominate microbiome dynamics in wild populations of kissing bugs (Triatominae)

BackgroundKissing bugs (Triatominae) are blood-feeding insects best known as the vectors of Trypanosoma cruzi, the causative agent of Chagas disease. Considering the high epidemiological relevance of these vectors, their biology and bacterial symbiosis remains surprisingly understudied. While previous investigations revealed generally low individual complexity but high among-individual variability of the triatomine microbiomes, any consistent microbiome determinants have not yet been identified across multiple Triatominae species. MethodsTo obtain a more comprehensive view of triatomine microbiomes, we investigated the host-microbiome relationship of five Triatoma species sampled from white-throated woodrat (Neotoma albigula) nests in multiple locations across the USA. We applied optimized 16S rRNA gene metabarcoding with a novel 18S rRNA gene blocking primer to a set of 170 T. cruzi negative individuals across all six instars. ResultsTriatomine gut microbiome composition is strongly influenced by three principal factors: ontogeny, species identity, and the environment. The microbiomes are characterised by significant loss in bacterial diversity throughout ontogenetic development. First instars possess the highest bacterial diversity while adult microbiomes are routinely dominated by a single taxon. Primarily, the bacterial genus Dietzia dominates late-stage nymphs and adults of T. rubida, T. protracta, and T. lecticularia, but is not present in the phylogenetically more distant T. gerstaeckeri and T. sanguisuga. Species-specific microbiome composition, particularly pronounced in early instars, is further modulated by locality-specific effects. In addition, pathogenic bacteria of the genus Bartonella, acquired from the vertebrate hosts, are an abundant component of Triatoma microbiomes. ConclusionOur study is the first to demonstrate deterministic patterns in microbiome composition among all life stages and multiple Triatoma species. We hypothesize that triatomine microbiome assemblages are produced by species- and life stage-dependent uptake of environmental bacteria and multiple indirect transmission strategies that promote bacterial transfer between individuals. Altogether, our study highlights the complexity of Triatominae symbiosis with bacteria and warrant further investigation to understand microbiome function in these important vectors.

ecology↗

bioRxiv2020

Host "cleansing zone" at secondary contact: a new pattern in host-parasite population genetics.

We introduce a new pattern of population genetic structure in a host-parasite system that can arise after secondary contact (SC) of previously isolated populations. Due to different generation time and therefore different tempo of molecular evolution the host and parasite populations reach different degrees of genetic differentiation during their separation (e.g. in refugia). Consequently, during the SC the host populations are able to re-establish a single panmictic population across the whole recolonized area, while the parasite populations stop their dispersal at the SC zone and create a narrow hybrid zone (HZ). From the hosts perspective, the parasites HZ functions on a microevolutionary scale as a "host-cleansing filter": while passing from area A to area B, the hosts are rid of the area A parasites and acquire the area B parasites. We demonstrate this novel pattern on a model composed of Apodemus mice and Polyplax lice by comparing maternally inherited markers (complete mitochondrial genomes, and complete genomes of vertically transmitted symbiont Legionella polyplacis) with SNPs derived from the louse genomic data. We discuss circumstances which may lead to this pattern and possible reasons why it has been overlooked in the studies on host-parasite population genetics.

evolutionary biology↗

bioRxiv2019

A new symbiotic lineage related to Neisseria and Snodgrassella arises from the dynamic and diverse microbiomes in sucking lice

Phylogenetic diversity of symbiotic bacteria in sucking lice suggests that lice have experienced a complex history of symbiont acquisition, loss, and replacement during their evolution. By combining metagenomics and amplicon screening across several populations of two louse genera (Polyplax and Hoplopleura) we describe a novel louse symbiont lineage related to Neisseria and Snodgrassella, and show its independent origin within dynamic lice microbiomes. While the genomes of these symbionts are highly similar in both lice genera, their respective distributions and status within lice microbiomes indicate that they have different functions and history. In Hoplopleura acanthopus, the Neisseria-related bacterium is a dominant obligate symbiont universally present across several hosts populations, and seems to be replacing a presumably older and more degenerated obligate symbiont. In contrast, the Polyplax microbiomes are dominated by the obligate symbiont Legionella polyplacis, with the Neisseria-related bacterium co-occurring only in some samples and with much lower abundance.

evolutionary biology↗

bioRxiv2019

Insect-symbiont gene expression in the midgut bacteriocytes of a blood-sucking parasite

BackgroundAnimals interact with a diverse array of both beneficial and detrimental microorganisms. These interactions sometimes spark obligate symbioses where the host depends on beneficial bacteria for survival and reproduction. In insects, these obligate symbioses in many cases allow feeding on nutritionally unbalanced diets such as plant sap and vertebrate blood. It is, however, still not clear how are these obligate intracellular symbioses maintained at the cellular level for up to several hundred million years. Exact mechanisms driving host-symbiont interactions are only understood for a handful of model species and data on blood-feeding hosts with intracellular bacteria are particularly scarce.\n\nResultsHere, we analyzed interactions at the symbiotic interfaces of an obligately blood-sucking parasite of sheep, the louse fly Melophagus ovinus. We assembled a reference transcriptome from one male and one female individual and used RNA-Seq with five biological replicates to compare expression in the midgut cells housing bacteria to the rest of the gut (foregut-hindgut). We focused on nutritional and immunity interactions between the insect host and its obligate symbiont Arsenophonus melophagi, and also generated lower-coverage data for three facultative bacterial symbionts (Sodalis melophagi, Bartonella melophagi, and Wolbachia sp.) and one facultative eukaryote Trypanosoma melophagium. We found strong evidence for the importance of zinc in the system likely caused by symbionts using zinc-dependent proteases when acquiring amino acids, and for likely different immunity mechanisms controlling the symbionts than in closely related tsetse flies.\n\nConclusionsOur results show that cellular and nutritional interactions between this blood-sucking insect and its symbionts are less intimate than what was previously found in some (but not all) plant-sap sucking insects such as aphids, psyllids, whiteflies, and mealybugs. This finding is likely interconnected to several features observed in symbionts in blood-sucking arthropods, particularly their midgut intracellular localization (as opposed to being localized in truly specialized bacteriocytes), intracytoplasmic presence (as opposed to having an outermost host-derived symbiosomal membrane), less severe genome reduction, and relatively recent associations caused by frequent evolutionary losses and replacements.\n\nData depositionRaw RNA-Seq data were made available through the European Nucleotide Archive (ENA) database under the study accession number PRJEB30632. All assemblies and additional large supplementary files are available on FigShare [https://doi.org/10.6084/m9.figshare.6146777.v1]. All commands used for data analyses are available on Github [https://github.com/filip-husnik/melophagus].

genomics↗

bioRxiv2018

Microbiomes of North American Triatominae: the grounds for Chagas disease epidemiology

AbstarctInsect microbiomes influence many fundamental host traits, including functions of practical significance such as their capacity as vectors to transmit parasites and pathogens. The knowledge on the diversity and development of the gut microbiomes in various blood feeding insects is thus crucial not only for theoretical purposes, but also for the development of better disease control strategies. In Triatominae (Heteroptera: Reduviidae), the blood feeding vectors of Chagas disease in South America and parts of North America, the investigation of the microbiomes is in its infancy. The few studies done on microbiomes of South American Triatominae species indicate a relatively low taxonomic diversity and a high host specificity. We designed a comparative survey to serve several purposes: I) to obtain a better insight into the overall microbiome diversity in different species, II) to check the long term stability of the interspecific differences, III) to describe the ontogenetic changes of the microbiome, and IV) to determine the potential correlation between microbiome composition and presence in the vector gut of Trypanosoma cruzi, the causative agent of Chagas disease. Using 16S amplicons of two abundant species from the southern US, and four laboratory reared colonies, we showed that the microbiome composition is determined by host species, rather than locality or environment. The OTUs (Operational Taxonomic Units) determination confirms a low microbiome diversity, with 12-17 main OTUs detected in wild populations of T. sanguisuga and T. protracta. Among the dominant bacterial taxa are Acinetobacter and Proteiniphilum but also the symbiotic bacterium Arsenophonus triatominarum, previously believed to only live intracellularly. The possibility of ontogenic microbiome changes was evaluated in all six developmental stages and faeces of the laboratory reared model Rhodnius prolixus. We detected considerable changes along the hosts ontogeny, including clear trends in the abundance variation of the three dominant bacteria, namely Enterococcus, Acinetobacter and Arsenophonus. Finally, we screened the samples for the presence of T. cruzi. Comparing the parasite presence with the microbiome composition, we assessed the possible significance of the latter in the epidemiology of the disease. Particularly, we found a trend towards more diverse microbiomes in T. cruzi positive T. protracta specimens.

microbiology↗

bioRxiv2017

Legionella becoming a mutualist: adaptive processes shaping the genome of symbiont in the louse Polyplax serrata

Legionellaceae are intracellular bacteria known as important pathogens of man. In the environment, they are mainly found in biofilms associated with amoebas. In contrast to another gammaproteobacterial family Enterobacteriaceae which established a broad spectrum of symbioses with many insect taxa, the only instance of legionella-like symbiont has been reported from lice of the genus Polyplax. Here, we sequenced the complete genome of this symbiont and compared its main characteristics to other Legionella species and insect symbionts. Based on rigorous multigene phylogenetic analyses, we confirm this bacterium as a member of the genus Legionella and propose the name Candidatus Legionella polyplacis, sp.n. We show that the genome of Ca. Legionella polyplacis underwent massive degeneration, including considerable size reduction (529.746 bp, 484 protein coding genes) and a severe decrease in GC content (23%). We identify several possible constraints underlying the evolution of this bacterium. On one hand, Ca. Legionella polyplacis and the louse symbionts Riesia and Puchtella experienced convergent evolution, perhaps due to adaptation to similar hosts. On the other hand, some metabolic differences are likely to reflect different phylogenetic positions of the symbionts and hence availability of particular metabolic function in the ancestor. This is exemplified by different arrangements of thiamine metabolism in Ca. Legionella polyplacis and Riesia. Finally, horizontal gene transfer is shown to play a significant role in the adaptive and diversification process. Particularly, we show that Ca. L. polyplacis horizontally acquired a complete biotin operon (bioADCHFB) that likely assisted this bacterium when becoming an obligate mutualist.

evolutionary biology↗