Morphological and molecular characterization of a sexually reproducing colony of the booklouse Liposcelis bostrychophila (Psocodea: Liposcelididae) found in Arizona

Booklice Liposcelis bostrychophila naturally infected by Rickettsia felis cause fever and experimental pneumonia in mammals

BACKGROUND

Rickettsia felis is emergent in tropical areas. Despite its high morbidity, its natural history has not yet been fully determined. We investigated the role of the common household booklouse, Liposcelis bostrychophila, recently found to harbour R. felis.

METHODS

Blood samples from 372 febrile patients from Senegalese villages, as well as nasal and skin samples from 264 asymptomatic individuals, were tested for cat flea-associated and booklice-associated strains of R. felis. Dust samples from beds were collected to isolate booklice and R. felis. Mice were infected with aerosol of R. felis strain from naturally infected booklice.

RESULTS

Forty febrile patients (11%) were infected by R. felis, including 26 (7%) by the booklice-associated strain. Nine nasal samples (3.4%) and 28 skin samples (10.6%) contained R. felis, including seven and 24, respectively, with the booklice-associated strain. The presence of live L. bostrychophila was observed in 32 dust samples (16.8%); R. felis was identified in 62 dust samples (32.5%). Several mice samples were positive for R. felis; interstitial lymphohistiocytic infiltrates were identified in lungs.

CONCLUSIONS

L. bostrychophila may be a reservoir of R. felis. The booklice-associated strain is pathogenic in mammals causing pneumonia. Human infection may be acquired via inhalation of infected booklice particles.

Cryptic Genes for Interbacterial Antagonism Distinguish Rickettsia Species Infecting Blacklegged Ticks From Other Rickettsia Pathogens

Background

The genus Rickettsia (Alphaproteobacteria: Rickettsiales) encompasses numerous obligate intracellular species with predominantly ciliate and arthropod hosts. Notable species are pathogens transmitted to mammals by blood-feeding arthropods. Mammalian pathogenicity evolved from basal, non-pathogenic host-associations; however, some non-pathogens are closely related to pathogens. One such species, Rickettsia buchneri, is prevalent in the blacklegged tick, Ixodes scapularis. While I. scapularis transmits several pathogens to humans, it does not transmit Rickettsia pathogens. We hypothesize that R. buchneri established a mutualism with I. scapularis, blocking tick superinfection with Rickettsia pathogens.

Methods

To improve estimates for assessing R. buchneri infection frequency in blacklegged tick populations, we used comparative genomics to identify an R. buchneri gene (REIS_1424) not present in other Rickettsia species present throughout the I. scapularis geographic range. Bioinformatic and phylogenomics approaches were employed to propose a function for the hypothetical protein (263 aa) encoded by REIS_1424.

Results

REIS_1424 has few analogs in other Rickettsiales genomes and greatest similarity to non-Proteobacteria proteins. This cohort of proteins varies greatly in size and domain composition, possessing characteristics of Recombination hotspot (Rhs) and contact dependent growth inhibition (CDI) toxins, with similarity limited to proximal C-termini (~145 aa). This domain was named CDI-like/Rhs-like C-terminal toxin (CRCT). As such proteins are often found as toxin-antidote (TA) modules, we interrogated REIS_1423 (151 aa) as a putative antidote. Indeed, REIS_1423 is similar to proteins encoded upstream of CRCT domain-containing proteins. Accordingly, we named these proteins CDI-like/Rhs-like C-terminal toxin antidotes (CRCA). R. buchneri expressed both REIS_1423 and REIS_1424 in tick cell culture, and PCR assays showed specificity for R. buchneri over other rickettsiae and utility for positive detection in three tick populations. Finally, phylogenomics analyses uncovered divergent CRCT/CRCA modules in varying states of conservation; however, only R. buchneri and related Tamurae/Ixodes Group rickettsiae carry complete TA modules.

Conclusion

We hypothesize that Rickettsia CRCT/CRCA modules circulate in the Rickettsia mobile gene pool, arming rickettsiae for battle over arthropod colonization. While its functional significance remains to be tested, R. buchneri CRCT/CRCA serves as a marker to positively identify infection and begin deciphering the role this endosymbiont plays in the biology of the blacklegged tick.

Fragmentation in mitochondrial genomes in relation to elevated sequence divergence and extreme rearrangements

Background

A single circular mitochondrial (mt) genome is a common feature across most metazoans. The mt-genome includes protein-coding genes involved in oxidative phosphorylation, as well as RNAs necessary for translation of mt-RNAs, whose order and number are highly conserved across animal clades, with few known exceptions of alternative mt-gene order or mt-genome architectures. One such exception consists of the fragmented mitochondrial genome, a type of genome architecture where mt-genes are split across two or more mt-chromosomes. However, the origins of mt-genome fragmentation and its effects on mt-genome evolution are unknown. Here, we investigate these origin and potential mechanisms underlying mt-genome fragmentation, focusing on a genus of booklice, Liposcelis, which exhibits elevated sequence divergence, frequent rearrangement of mt-gene order, and fragmentation of the mt genome, and compare them to other Metazoan clades.

Results

We found this genus Liposcelis exhibits very low conservation of mt-gene order across species, relative to other metazoans. Levels of gene order rearrangement were, however, unrelated to whether or not mt-genomes were fragmented or intact, suggesting mitochondrial genome fragmentation is not affecting mt-gene order directly. We further investigated possible mechanisms underpinning these patterns and revealed very high conservation of non-coding sequences at the edges of multiple recombination regions across populations of one particular Liposcelis species, supportive of a hypothesis that mt-fragmentation arises from recombination errors between mt-genome copies. We propose these errors may arise as a consequence of a heightened mutation rate in clades exhibiting mt-fragmentation. Consistent with this, we observed a striking pattern across three Metazoan phyla (Arthropoda, Nematoda, Cnidaria) characterised by members exhibiting high levels of mt-gene order rearrangement and cases of mt-fragmentation, whereby the mt-genomes of species more closely related to species with fragmented mt-genomes diverge more rapidly despite experiencing strong purifying selection.

Conclusions

We showed that contrary to expectations, mt-genome fragmentation is not correlated with the increase in mt-genome rearrangements. Furthermore, we present evidence that fragmentation of the mt-genome may be part of a general relaxation of a natural selection on the mt-genome, thus providing new insights into the origins of mt-genome fragmentation and evolution.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01218-7.

Morphological and molecular identification of arrhenotokous strain of Diglyphuswani (Hymenoptera, Eulophidae) found in China as a control agent against agromyzid leafminers

Diglyphus species are ecologically and economically important on agromyzid leafminers. In 2018, a thelytokous species, Diglyphuswani Liu, Zhu & Yefremova, was firstly reported and described. Subsequently, the arrhenotokous D.wani were discovered in Yunnan and Guizhou Provinces of China. We compared the morphological characteristics of thelytokous and arrhenotokous strains. However, the females of two strains had a strongly similar morphology and showed subtle differences in fore- and hind-wings. The difference was that forewing of arrhenotokous female was with denser setae overall, showing that costal cell with 2 ~ 4 rows of setae on dorsal surface and the setae of basal cell with 15 ~ 21 hairs and forewing of thelytokous female was with two rows of setae on dorsal surface and basal cell with 10 ~ 15 hairs generally. The setation beneath the marginal vein of the hind-wing of arrhenotokous female is denser than the same area of thelytokous female. To explore the genetic divergence between thelytokous and arrhenotokous strains of D.wani, the mitochondrial and nuclear gene were applied and sequenced. The polygenic analyses revealed that two strains can be distinguished by COI, ITS1 and ITS2. The mean sequence divergence between the two strains was 0.052, 0.010 and 0.007, respectively. Nevertheless, the 28S gene was unfeasible due to its containing a sharing haplotype between different strains. The two strains of D.wani are dominant parasitoids against agromyzid leafminers and such effective discernible foundation provides future in-depth studies on biological characteristics, along with insight into field application of two strains of D.wani.

Evolution of Wolbachia mutualism and reproductive parasitism: insight from two novel strains that co-infect cat fleas

Wolbachiae are obligate intracellular bacteria that infect arthropods and certain nematodes. Usually maternally inherited, they may provision nutrients to (mutualism) or alter sexual biology of (reproductive parasitism) their invertebrate hosts. We report the assembly of closed genomes for two novel wolbachiae, wCfeT and wCfeJ, found co-infecting cat fleas (Ctenocephalides felis) of the Elward Laboratory colony (Soquel, CA, USA). wCfeT is basal to nearly all described Wolbachia supergroups, while wCfeJ is related to supergroups C, D and F. Both genomes contain laterally transferred genes that inform on the evolution of Wolbachia host associations. wCfeT carries the Biotin synthesis Operon of Obligate intracellular Microbes (BOOM); our analyses reveal five independent acquisitions of BOOM across the Wolbachia tree, indicating parallel evolution towards mutualism. Alternately, wCfeJ harbors a toxin-antidote operon analogous to the wPip cinAB operon recently characterized as an inducer of cytoplasmic incompatibility (CI) in flies. wCfeJ cinB and three adjacent genes are collectively similar to large modular toxins encoded in CI-like operons of certain Wolbachia strains and Rickettsia species, signifying that CI toxins streamline by fission of large modular toxins. Remarkably, the C. felis genome itself contains two CI-like antidote genes, divergent from wCfeJ cinA, revealing episodic reproductive parasitism in cat fleas and evidencing mobility of CI loci independent of WO-phage. Additional screening revealed predominant co-infection (wCfeT/wCfeJ) amongst C. felis colonies, though fleas in wild populations mostly harbor wCfeT alone. Collectively, genomes of wCfeT, wCfeJ, and their cat flea host supply instances of lateral gene transfers that could drive transitions between parasitism and mutualism.

No signal of deleterious mutation accumulation in conserved gene sequences of extant asexual hexapods

Loss of sex and recombination is generally assumed to impede the effectiveness of purifying selection and to result in the accumulation of slightly deleterious mutations. Empirical evidence for this has come from several studies investigating mutational load in a small number of individual genes. However, recent whole transcriptome based studies have yielded inconsistent results, hence questioning the validity of the assumption of mutational meltdown in asexual populations. Here, we study the effectiveness of purifying selection in eight asexual hexapod lineages and their sexual relatives, as present in the 1 K Insect Transcriptome Evolution (1KITE) project, covering eight hexapod groups. We analyse the accumulation of slightly deleterious nonsynonymous and synonymous point mutations in 99 single copy orthologue protein-coding loci shared among the investigated taxa. While accumulation rates of nonsynonymous mutations differed between genes and hexapod groups, we found no effect of reproductive mode on the effectiveness of purifying selection acting at nonsynonymous and synonymous sites. Although the setup of this study does not fully rule out nondetection of subtle effects, our data does not support the established consensus of asexual lineages undergoing ‘mutational meltdown’.

A Tangled Web: Origins of Reproductive Parasitism

While typically a flea parasite and opportunistic human pathogen, the presence of Rickettsia felis (strain LSU-Lb) in the non-blood-feeding, parthenogenetically reproducing booklouse, Liposcelis bostrychophila, provides a system to ascertain factors governing not only host transitions but also obligate reproductive parasitism (RP). Analysis of plasmid pLbAR, unique to R. felis str. LSU-Lb, revealed a toxin–antitoxin module with similar features to prophage-encoded toxin–antitoxin modules utilized by parasitic Wolbachia strains to induce another form of RP, cytoplasmic incompatibility, in their arthropod hosts. Curiously, multiple deubiquitinase and nuclease domains of the large (3,841 aa) pLbAR toxin, as well the entire antitoxin, facilitated the detection of an assortment of related proteins from diverse intracellular bacteria, including other reproductive parasites. Our description of these remarkable components of the intracellular mobilome, including their presence in certain arthropod genomes, lends insight on the evolution of RP, while invigorating research on parasite-mediated biocontrol of arthropod-borne viral and bacterial pathogens.

Evaluation of Light Attraction for the Stored-Product Psocids, Liposcelis entomophila, Liposcelis paeta, and Liposcelis brunnea

Psocids have become global pests of stored commodities as they can cause considerable economic losses. These insects are difficult to control because they have developed resistance to many chemical insecticides. Therefore, it is crucial to investigate alternative integrated pest management (IPM) approaches, such as the use of light attraction for monitoring and/or controlling psocids. Light attraction has been studied for Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae) but not for other psocid species. In this study, we investigated the response of adults of three psocid species (Psocoptera: Liposcelididae), Liposcelis entomophila (Enderlein), Liposcelis paeta Pearman, and Liposcelis brunnea Motschulsky, to six wavelengths of light from light-emitting diode (LED) in paired-choice pitfall tests. L. entomophila females and males were not attracted to any of the wavelengths tested. L. paeta females responded positively to two ultraviolet (UV) wavelengths (351 and 400 nm) and to green light (527 nm), while males did not respond to any light. L. brunnea females and males responded positively to all six wavelengths evaluated. Most of the LEDs that elicited positive responses to L. paeta females and L. brunnea females and males were also preferred when these lights were presented against brewer's yeast, a food attractant highly preferred by several psocid species. Females of L. paeta and L. brunnea were attracted to white light when compared with a blank, but females of L. entomophila were not attracted to white light compared to a blank.

The Highly Divergent Mitochondrial Genomes Indicate That the Booklouse, Liposcelis bostrychophila (Psocoptera: Liposcelididae) Is a Cryptic Species

The booklouse, Liposcelis bostrychophila is an important storage pest worldwide. The mitochondrial (mt) genome of an asexual strain (Beibei, China) of the L. bostrychophila comprises two chromosomes; each chromosome contains approximate half of the 37 genes typically found in bilateral animals. The mt genomes of two sexual strains of L. bostrychophila, however, comprise five and seven chromosomes, respectively; each chromosome contains one to six genes. To understand mt genome evolution in L. bostrychophila, and whether L. bostrychophila is a cryptic species, we sequenced the mt genomes of six strains of asexual L. bostrychophila collected from different locations in China, Croatia, and the United States. The mt genomes of all six asexual strains of L. bostrychophila have two chromosomes. Phylogenetic analysis of mt genome sequences divided nine strains of L. bostrychophila into four groups. Each group has a distinct mt genome organization and substantial sequence divergence (48.7–87.4%) from other groups. Furthermore, the seven asexual strains of L. bostrychophila, including the published Beibei strain, are more closely related to two other species of booklice, L. paeta and L. sculptilimacula, than to the sexual strains of L. bostrychophila. Our results revealed highly divergent mt genomes in the booklouse, L. bostrychophila, and indicate that L. bostrychophila is a cryptic species.

Wholly Rickettsia! Reconstructed Metabolic Profile of the Quintessential Bacterial Parasite of Eukaryotic Cells

Reductive genome evolution has purged many metabolic pathways from obligate intracellular Rickettsia (Alphaproteobacteria; Rickettsiaceae). While some aspects of host-dependent rickettsial metabolism have been characterized, the array of host-acquired metabolites and their cognate transporters remains unknown. This dearth of information has thwarted efforts to obtain an axenic Rickettsia culture, a major impediment to conventional genetic approaches. Using phylogenomics and computational pathway analysis, we reconstructed the Rickettsia metabolic and transport network, identifying 51 host-acquired metabolites (only 21 previously characterized) needed to compensate for degraded biosynthesis pathways. In the absence of glycolysis and the pentose phosphate pathway, cell envelope glycoconjugates are synthesized from three imported host sugars, with a range of additional host-acquired metabolites fueling the tricarboxylic acid cycle. Fatty acid and glycerophospholipid pathways also initiate from host precursors, and import of both isoprenes and terpenoids is required for the synthesis of ubiquinone and the lipid carrier of lipid I and O-antigen. Unlike metabolite-provisioning bacterial symbionts of arthropods, rickettsiae cannot synthesize B vitamins or most other cofactors, accentuating their parasitic nature. Six biosynthesis pathways contain holes (missing enzymes); similar patterns in taxonomically diverse bacteria suggest alternative enzymes that await discovery. A paucity of characterized and predicted transporters emphasizes the knowledge gap concerning how rickettsiae import host metabolites, some of which are large and not known to be transported by bacteria. Collectively, our reconstructed metabolic network offers clues to how rickettsiae hijack host metabolic pathways. This blueprint for growth determinants is an important step toward the design of axenic media to rescue rickettsiae from the eukaryotic cell.IMPORTANCE A hallmark of obligate intracellular bacteria is the tradeoff of metabolic genes for the ability to acquire host metabolites. For species of Rickettsia, arthropod-borne parasites with the potential to cause serious human disease, the range of pilfered host metabolites is unknown. This information is critical for dissociating rickettsiae from eukaryotic cells to facilitate rickettsial genetic manipulation. In this study, we reconstructed the Rickettsia metabolic network and identified 51 host metabolites required to compensate patchwork Rickettsia biosynthesis pathways. Remarkably, some metabolites are not known to be transported by any bacteria, and overall, few cognate transporters were identified. Several pathways contain missing enzymes, yet similar pathways in unrelated bacteria indicate convergence and possible novel enzymes awaiting characterization. Our work illuminates the parasitic nature by which rickettsiae hijack host metabolism to counterbalance numerous disintegrated biosynthesis pathways that have arisen through evolution within the eukaryotic cell. This metabolic blueprint reveals what a Rickettsia axenic medium might entail.

Rickettsia felis: The Complex Journey of an Emergent Human Pathogen

Rickettsia felis is an obligate intracellular bacterium that is different from other officially recognized rickettsial species. It has multiple genes of different origins, an incubation temperature of less than 32°C, and a conjugative plasmid. This Rickettsia is commonly detected in febrile patients in sub-Saharan Africa. R. felis is frequently detected in cat fleas, but recently mosquitoes have been suspected to be able to transmit the bacterium. However, many aspects of the ecology and epidemiology of R. felis are not completely understood and remain to be uncovered. We aim here to give an update of the current knowledge about this fascinating organism.