Spider phylosymbiosis: divergence of widow spider species and their tissues' microbiomes

Diversity and Functionality of Bacteria Associated with Different Tissues of Spider Heteropoda venatoria Revealed through Integration of High-Throughput Sequencing and Culturomics Approaches

Spiders host a diverse range of bacteria in their guts and other tissues, which have been found to play a significant role in their fitness. This study aimed to investigate the community diversity and functional characteristics of spider-associated bacteria in four tissues of Heteropoda venatoria using HTS of the 16S rRNA gene and culturomics technologies, as well as the functional verification of the isolated strains. The results of HTS showed that the spider-associated bacteria in different tissues belonged to 34 phyla, 72 classes, 170 orders, 277 families, and 458 genera. Bacillus was found to be the most abundant bacteria in the venom gland, silk gland, and ovary, while Stenotrophomonas, Acinetobacter, and Sphingomonas were dominant in the gut microbiota. Based on the amplicon sequencing results, 21 distinct cultivation conditions were developed using culturomics to isolate bacteria from the ovary, gut, venom gland, and silk gland. A total of 119 bacterial strains, representing 4 phyla and 25 genera, with Bacillus and Serratia as the dominant genera, were isolated. Five strains exhibited high efficiency in degrading pesticides in the in vitro experiments. Out of the 119 isolates, 28 exhibited antibacterial activity against at least one of the tested bacterial strains, including the pathogenic bacteria Staphylococcus aureus, Acinetobacter baumanii, and Enterococcus faecalis. The study also identified three strains, GL312, PL211, and PL316, which exhibited significant cytotoxicity against MGC-803. The crude extract from the fermentation broth of strain PL316 was found to effectively induce apoptosis in MGC-803 cells. Overall, this study offers a comprehensive understanding of the bacterial community structure associated with H. venatoria. It also provides valuable insights into discovering novel antitumor natural products for gastric cancer and xenobiotic-degrading bacteria of spiders.

Endosymbiont diversity across native and invasive brown widow spider populations

The invasive brown widow spider, Latrodectus geometricus (Araneae: Theridiidae), has spread in multiple locations around the world and, along with it, brought associated organisms such as endosymbionts. We investigated endosymbiont diversity and prevalence across putative native and invasive populations of this spider, predicting lower endosymbiont diversity across the invasive range compared to the native range. First, we characterized the microbial community in the putative native (South Africa) and invasive (Israel and the United States) ranges via high throughput 16S sequencing of 103 adult females. All specimens were dominated by reads from only 1-3 amplicon sequence variants (ASV), and most individuals were infected with an apparently uniform strain of Rhabdochlamydia. We also found Rhabdochlamydia in spider eggs, indicating that it is a maternally-inherited endosymbiont. Relatively few other ASV were detected, but included two variant Rhabdochlamydia strains and several Wolbachia, Spiroplasma and Enterobacteriaceae strains. We then diagnostically screened 118 adult female spiders from native and invasive populations specifically for Rhabdochlamydia and Wolbachia. We found Rhabdochlamydia in 86% of individuals and represented in all populations, which suggests that it is a consistent and potentially important associate of L. geometricus. Wolbachia was found at lower overall prevalence (14%) and was represented in all countries, but not all populations. In addition, we found evidence for geographic variation in endosymbiont prevalence: spiders from Israel were more likely to carry Rhabdochlamydia than those from the US and South Africa, and Wolbachia was geographically clustered in both Israel and South Africa. Characterizing endosymbiont prevalence and diversity is a first step in understanding their function inside the host and may shed light on the process of spread and population variability in cosmopolitan invasive species.

Food provisioning to Pardosa spiders decreases the levels of tissue-resident endosymbiotic bacteria

The diversity, host specificity, and physiological effects of endosymbiotic bacteria in spiders (Araneae) are poorly characterized. We used 16S rDNA sequencing to evaluate endosymbionts in the cephalothorax and legs of a wolf spider Pardosa agrestis. We tested the effects of feeding once or twice daily with fruit flies, aphids, or starved and compared them to those of syntopically occurring Pardosa palustris. The feeding increased traveled distance up to five times in some of the groups provisioned with food relative to the starved control. The Shannon diversity t-test revealed significant differences between these component communities of the two spider species. The increased frequency of feeding with fruit flies, but not aphids, increased the dominance and decreased the alpha diversity of OTUs. The obligate or facultative endosymbionts were present in all analyzed spider individuals and were represented mostly by Rickettsiella, Rhabdochlamydia, Spiroplasma, and the facultative intracellular parasite Legionella. Vertically transmitted endosymbionts were less common, represented by Wolbachia pipientis and Rickettsia sp. H820. The relative abundance of Mycoplasma spp. was negatively correlated with provisioned or killed aphids. In conclusion, the tissues of Pardosa spiders host tremendously diverse assemblages of bacteria, including obligate or facultative endosymbionts, with yet unknown phenotypic effects.

The influence of species identity and geographic locations on gut microbiota of small rodents

Although the correlation between gut microbiota, species identity and geographic locations has long attracted the interest of scientists, to what extent species identity and geographic locations influence the gut microbiota assemblages in granivorous rodents needs further investigation. In this study, we performed a survey of gut microbial communities of four rodent species (Apodemus agrarius, A. peninsulae, Tamias sibiricus and Clethrionomys rufocanus) distributed in two areas with great distance (> 600 km apart), to assess if species identity dominates over geographic locations in shaping gut microbial profiles using 16S rRNA gene sequencing. We found that gut microbiota composition varied significantly across host species and was closely correlated with host genetics. We identified strong species identity effects on gut microbial composition, with a comparatively weaker signal of geographic provenance on the intestinal microbiota. Specifically, microbiota of one species was on average more similar to that of conspecifics living in separate sites than to members of a closely related species living in the same location. Our study suggests that both host genetics and geographical variations influence gut microbial diversity of four rodent species, which merits further investigation to reveal the patterns of phylogenetic correlation of gut microbial community assembly in mammals across multiple habitats.

The Phylosymbiosis Pattern Between the Fig Wasps of the Same Genus and Their Associated Microbiota

Microbial communities can be critical for many metazoans, which can lead to the observation of phylosymbiosis with phylogenetically related species sharing similar microbial communities. Most of the previous studies on phylosymbiosis were conducted across the host families or genera. However, it is unclear whether the phylosymbiosis signal is still prevalent at lower taxonomic levels. In this study, 54 individuals from six species of the fig wasp genus Ceratosolen (Hymenoptera: Agaonidae) collected from nine natural populations and their associated microbiota were investigated. The fig wasp species were morphologically identified and further determined by mitochondrial CO1 gene fragments and nuclear ITS2 sequences, and the V4 region of 16S rRNA gene was sequenced to analyze the bacterial communities. The results suggest a significant positive correlation between host genetic characteristics and microbial diversity characteristics, indicating the phylosymbiosis signal between the phylogeny of insect hosts and the associated microbiota in the lower classification level within a genus. Moreover, we found that the endosymbiotic Wolbachia carried by fig wasps led to a decrease in bacterial diversity of host-associated microbial communities. This study contributes to our understanding of the role of host phylogeny, as well as the role of endosymbionts in shaping the host-associated microbial community.

Differing Dietary Nutrients and Diet-Associated Bacteria Has Limited Impact on Spider Gut Microbiota Composition

Spiders are a key predator of insects across ecosystems and possess great potential as pest control agents. Unfortunately, it is difficult to artificially cultivate multiple generations of most spider species. Since gut bacterial flora has been shown to significantly alter nutrient availability, it is plausible that the spiders' microbial community plays a key role in their unsuccessful breeding. However, both the gut microbial composition and its influencing factors in many spiders remain a mystery. In this study, the gut microbiota of Campanicola campanulata, specialists who prey on ants and are widely distributed across China, was characterized. After, the impact of diet and diet-associated bacteria on gut bacterial composition was evaluated. First, two species of prey ants (Lasius niger and Tetramorium caespitum) were collected from different locations and fed to C. campanulata. For each diet, we then profiled the nutritional content of the ants, as well as the bacterial communities of both the ants and spiders. Results showed that the protein and carbohydrate content varied between the two prey ant species. We isolated 682 genera from 356 families in the ants (dominant genera including Pseudomonas, Acinetobacter, Paraburkholderia, Staphylococcus, and Novosphingobium), and 456 genera from 258 families in the spiders (dominated by Pseudomonas). However, no significant differences were found in the gut microbiota of spiders that were fed the differing ants. Together, these results indicate that nutritional variation and diet-associated bacterial differences have a limited impact on the microbial composition of spider guts, highlighting that spiders may have a potentially stable internal environment and lay the foundation for future investigations into gut microbiota.

Species-specific but not phylosymbiotic gut microbiomes of New Guinean passerine birds are shaped by diet and flight-associated gut modifications

Animal hosts have evolved intricate associations with microbial symbionts, where both depend on each other for particular functions. In many cases, these associations lead to phylosymbiosis, where phylogenetically related species harbour compositionally more similar microbiomes than distantly related species. However, evidence for phylosymbiosis is either weak or lacking in gut microbiomes of flying vertebrates, particularly in birds. To shed more light on this phenomenon, we compared cloacal microbiomes of 37 tropical passerine bird species from New Guinea using 16S rRNA bacterial gene sequencing. We show a lack of phylosymbiosis and document highly variable microbiomes. Furthermore, we find that gut bacterial community compositions are species-specific and tend to be shaped by host diet but not sampling locality, potentially driven by the similarities in habitats used by individual species. We further show that flight-associated gut modifications, coupled with individual dietary differences, shape gut microbiome structure and variation, contributing to the lack of phylosymbiosis. These patterns indicate that the stability of symbiosis may depend on microbial functional diversity rather than taxonomic composition. Furthermore, the more variable and fluid host-microbe associations suggest probable disparities in the potential for coevolution between bird host species and microbial symbionts.

Genomes of Gut Bacteria from Nasonia Wasps Shed Light on Phylosymbiosis and Microbe-Assisted Hybrid Breakdown

Phylosymbiosis is a cross-system trend whereby microbial community relationships recapitulate the host phylogeny. In Nasonia parasitoid wasps, phylosymbiosis occurs throughout development, is distinguishable between sexes, and benefits host development and survival. Moreover, the microbiome shifts in hybrids as a rare Proteus bacterium in the microbiome becomes dominant. The larval hybrids then catastrophically succumb to bacterium-assisted lethality and reproductive isolation between the species. Two important questions for understanding phylosymbiosis and bacterium-assisted lethality in hybrids are (i) do the Nasonia bacterial genomes differ from other animal isolates and (ii) are the hybrid bacterial genomes the same as those in the parental species? Here, we report the cultivation, whole-genome sequencing, and comparative analyses of the most abundant gut bacteria in Nasonia larvae, Providencia rettgeri and Proteus mirabilis. Characterization of new isolates shows Proteus mirabilis forms a more robust biofilm than Providencia rettgeri and that, when grown in coculture, Proteus mirabilis significantly outcompetes Providencia rettgeri. Providencia rettgeri genomes from Nasonia are similar to each other and more divergent from pathogenic, human associates. Proteus mirabilis from Nasonia vitripennis, Nasonia giraulti, and their hybrid offspring are nearly identical and relatively distinct from human isolates. These results indicate that members of the larval gut microbiome within Nasonia are most similar to each other, and the strain of the dominant Proteus mirabilis in hybrids is resident in parental species. Holobiont interactions between shared, resident members of the wasp microbiome and the host underpin phylosymbiosis and hybrid breakdown.

IMPORTANCE Animal and plant hosts often establish intimate relationships with their microbiomes. In varied environments, closely related host species share more similar microbiomes, a pattern termed phylosymbiosis. When phylosymbiosis is functionally significant and beneficial, microbial transplants between host species and host hybridization can have detrimental consequences on host biology. In the Nasonia parasitoid wasp genus, which contains a phylosymbiotic gut community, both effects occur and provide evidence for selective pressures on the holobiont. Here, we show that bacterial genomes in Nasonia differ from other environments and harbor genes with unique functions that may regulate phylosymbiotic relationships. Furthermore, the bacteria in hybrids are identical to those in parental species, thus supporting a hologenomic tenet that the same members of the microbiome and the host genome impact phylosymbiosis, hybrid breakdown, and speciation.