Parasitic manipulation or by-product of infection: an experimental approach using trematode-infected snails

Natural selection should favour parasite genotypes that manipulate hosts in ways that enhance parasite fitness. However, it is also possible that the effects of infection are not adaptive. Here we experimentally examined the phenotypic effects of infection in a snail–trematode system. These trematodes (Atriophallophorus winterbourni) produce larval cysts within the snail's shell (Potamopyrgus antipodarum); hence the internal shell volume determines the total number of parasite cysts produced. Infected snails in the field tend to be larger than uninfected snails, suggesting the hypothesis that parasites manipulate host growth so as to increase the space available for trematode reproduction. To test the hypothesis, we exposed juvenile snails to trematode eggs. Snails were then left to grow for about one year in 800-l outdoor mesocosms. We found that uninfected males were smaller than uninfected females (sexual dimorphism). We also found that infection did not affect the shell dimensions of males. However, infected females were smaller than uninfected females. Hence, infection stunts the growth of females, and (contrary to the hypothesis) it results in a smaller internal volume for larval cysts. Finally, infected females resembled males in size and shape, suggesting the possibility that parasitic castration prevents the normal development of females. These results thus indicate that the parasite is not manipulating the growth of infected hosts so as to increase the number of larval cysts, although alternative adaptive explanations are possible.

Molecular Characterization of a Novel Virga-like Virus Isolated From Wheat

In this work, we report the isolation of a novel positive-sense single strand RNA virus from wheat, tentatively named Triticum aestivum-associated virga-like virus 1 (TaAVLV1). Further characterization revealed that the complete genome of TaAVLV1 was divided into two segments, RNA1 and RNA2, which were 3530 and 3466 nt long, excluding the polyA tail. These segments contained two open reading frames (ORFs). The ORF in RNA1 encoded an RNA-dependent RNA polymerase (RdRp), while the ORF in RNA2 encoded a putative protein carrying MET and HEL domains. Phylogenetic analysis based on the RdRp protein of each representative genus of Virgaviridae placed TaAVLV1 in the unclassified Virgaviridae clade of the Virgaviridae family. To our knowledge, this is the first report of virga-like virus isolated from wheat. Future studies will be conducted to examine its effect on host growth and development.

Microbiomes of Blood-Feeding Arthropods: Genes Coding for Essential Nutrients and Relation to Vector Fitness and Pathogenic Infections. A Review

Background: Blood-feeding arthropods support a diverse array of symbiotic microbes, some of which facilitate host growth and development whereas others are detrimental to vector-borne pathogens. We found a common core constituency among the microbiota of 16 different arthropod blood-sucking disease vectors, including Bacillaceae, Rickettsiaceae, Anaplasmataceae, Sphingomonadaceae, Enterobacteriaceae, Pseudomonadaceae, Moraxellaceae and Staphylococcaceae. By comparing 21 genomes of common bacterial symbionts in blood-feeding vectors versus non-blooding insects, we found that certain enteric bacteria benefit their hosts by upregulating numerous genes coding for essential nutrients. Bacteria of blood-sucking vectors expressed significantly more genes (p < 0.001) coding for these essential nutrients than those of non-blooding insects. Moreover, compared to endosymbionts, the genomes of enteric bacteria also contained significantly more genes (p < 0.001) that code for the synthesis of essential amino acids and proteins that detoxify reactive oxygen species. In contrast, microbes in non-blood-feeding insects expressed few gene families coding for these nutrient categories. We also discuss specific midgut bacteria essential for the normal development of pathogens (e.g., Leishmania) versus others that were detrimental (e.g., bacterial toxins in mosquitoes lethal to Plasmodium spp.).

Microbiome-Metabolome Analyze The Immune Microenvironment of Cecal Contents, Soft and Hard Feces of Hyplus Rabbits

Background: Intestinal microbiota and its metabolites play a vital role in host growth, development and immune regulation. Methods: This study analyzed the microbial community distribution, cytokines and short chain fatty acids (SCFAs) content of cecal contents (Con) group, soft feces (SF) group and hard feces (HF) group of 140-day-old Hyplus rabbits, and verified the effect of soft feces on cecal immune microenvironment by fasting soft feces.Results: The results showed that there were significant differences in the levels of phylum and genus composition, cytokines and SCFAs among Con group, SF group and HF group. In addition, metabolic pathway enrichment analysis found that there were two significantly up-regulated differential metabolic pathways in SF group and HF group compared with con group, P125-PWY, namely the super pathway of (R, R) - butanediol biosynthesis and P341-PWY, namely the glycolysis V pathway. At the same time, Christensenellaceae_R-7_Group and Lachnoclostridium are significantly enriched in the above two pathways. The correlation analysis of cytokines and SCFAs with differential microbial communities showed that Muribaculaceae and Ruminococcaceae_UCG-014, Ruminococcaceae_NK4A214_group and Christensenellaceae_R-7_Group are closely related to cytokines and SCFAs. After fasting soft feces (CP), the contents of SCFAs and cytokines (IL-4, IL-10) in cecum decreased significantly, while cytokines (TNF-a, IL-1β) increased significantly. The results of multiple immunofluorescence showed that the expression of claudin-1, occludin and ZO-1 related to intestinal immune barrier increased significantly in CP Group. Conclusions: In conclusion, soft feces are not only rich in probiotics and SCFAs, but also play a very important role in improving the immune microenvironment of cecum. This study may provide a valuable reference for the treatment of inflammatory intestinal diseases.

Microbial Surface Biofilm Responds to the Growth-Reproduction-Senescence Cycle of the Dominant Coral Reef Macroalgae Sargassum spp.

Macroalgae play an intricate role in microbial-mediated coral reef degradation processes due to the release of dissolved nutrients. However, temporal variabilities of macroalgal surface biofilms and their implication on the wider reef system remain poorly characterized. Here, we study the microbial biofilm of the dominant reef macroalgae Sargassum over a period of one year at an inshore Great Barrier Reef site (Magnetic Island, Australia). Monthly sampling of the Sargassum biofilm links the temporal taxonomic and putative functional metabolic microbiome changes, examined using 16S rRNA gene amplicon and metagenomic sequencing, to the pronounced growth-reproduction-senescence cycle of the host. Overall, the macroalgal biofilm was dominated by the heterotrophic phyla Firmicutes (35% ± 5.9% SD) and Bacteroidetes (12% ± 0.6% SD); their relative abundance ratio shifted significantly along the annual growth-reproduction-senescence cycle of Sargassum. For example, Firmicutes were 1.7 to 3.9 times more abundant during host growth and reproduction cycles than Bacteroidetes. Both phyla varied in their carbohydrate degradation capabilities; hence, temporal fluctuations in the carbohydrate availability are potentially linked to the observed shift. Dominant heterotrophic macroalgal biofilm members, such as Firmicutes and Bacteroidetes, are implicated in exacerbating or ameliorating the release of dissolved nutrients into the ambient environment, though their contribution to microbial-mediated reef degradation processes remains to be determined.

Intestinal GCN2 controls Drosophila systemic growth upon AA imbalance in response to Lactiplantibacillus plantarum symbiotic cues encoded by r/tRNA operons

Symbiotic bacteria support host growth upon malnutrition. How bacteria achieve this remains partly elusive. Here, we took advantage of the mutualism between Drosophila and Lactiplantibacillus plantarum (Lp) to investigate such mechanisms. Using chemically-defined holidic diets, we found that association with Lp improves the growth of larvae fed amino acid-imbalanced diets. We show that in this context Lp supports its host's growth through a molecular dialog that requires functional operons encoding ribosomal and transfer RNAs (r/tRNAs) in Lp and the GCN2 kinase in Drosophila's enterocytes. Our data indicate that Lp's r/tRNAs loci products activate GCN2 in a subset of larval enterocytes, a mechanism necessary for the host's adaptation to amino acid imbalance that ultimately supports growth. Our findings unravel a novel beneficial molecular dialog between hosts and microbes, which relies on a non-canonical role of GCN2 as a mediator of non-nutritional symbiotic cues encoded by r/tRNA operons.

The Promotion of Festuca sinensis under Heavy Metal Treatment Mediated by Epichloë Endophyte

To more clearly clarify the relationship between the Epichloë endophyte and its host, F. sinensis, the effects of Epichloë endophyte on F. sinensis performance under heavy metal treatment was investigated. The growth performance and physiology variations of F. sinensis with (E+) and without the endophyte (E−) were evaluated after they were subjected to Zn2+ and Cd2+ treatments. The results showed that heavy metal treatments had significant effects on plants, as the performance of plants under Zn2+ and Cd2+ treatments was significantly different with plants under control treatment (p < 0.05). Cd2+ treatments showed a hormesis effect, whereas Zn2+ did not. The endophyte increased host heavy metal stress tolerance by promoting host growth as the E+ plants had significantly higher plant height, tiller number, root length (p < 0.05). The endophyte also promoted ion uptake by the host and induced endogenous hormone production (p < 0.05). These results suggested that the Epichloë endophyte regulated host growth and physiology to improve association tolerance to environmental conditions. This study provides another example that the Epichloë endophyte can increase plant tolerance to metal stress.

Isolation and Identification of Plant Growth Promoting Rhizobacteria from Sago Palm (Metroxylon sagu, Rottb.)

Plant growth promoting rhizobacteria (PGPR) are strains of naturally occurring soil bacteria that live in close vicinity to the plant’s rhizosphere region which possess the capability to augment host growth. This study was conducted to isolate and identify potential PGPR isolates indigenous to Metroxylon sagu, Rottb. rhizosphere. These potential isolates were characterised based on their beneficial plant growth promoting (PGP) properties and identified by molecular analysis via 16S rDNA sequencing. A total of 18 isolates were successfully isolated, out of which five isolates were tested, and designated as (S1A, S2B, S3A, S3C and S42). Among the five isolates, two isolates (S2B and S3C) were found to produce high levels of indole-3-acetic acid (2.96 μg/mL and 10.31 μg/mL), able to fix nitrogen and show significant activity in phosphate solubilisation. The analysis of their sequences via National Center for Biotechnology Information (NCBI) suggested their close identity towards Lysinibacillus sphaericus and Bacillus thuringiensis. It can be concluded that the isolated PGPR possesses beneficial PGP attributes. It can be implied that the isolated PGPR are potential to be used as inoculant biofertilisers, beneficial for Metroxylon sagu, Rottb. growth. Hence, further studies need to be done to evaluate the effectiveness of the beneficial microbes towards sago seedlings growth, under pot experiment.

Emergent RNA–RNA interactions can promote stability in a facultative phototrophic endosymbiosis

Eukaryote–eukaryote endosymbiosis was responsible for the spread of chloroplast (plastid) organelles. Stability is required for the metabolic and genetic integration that drives the establishment of new organelles, yet the mechanisms that act to stabilize emergent endosymbioses—between two fundamentally selfish biological organisms—are unclear. Theory suggests that enforcement mechanisms, which punish misbehavior, may act to stabilize such interactions by resolving conflict. However, how such mechanisms can emerge in a facultative endosymbiosis has yet to be explored. Here, we propose that endosymbiont–host RNA–RNA interactions, arising from digestion of the endosymbiont population, can result in a cost to host growth for breakdown of the endosymbiosis. Using the model facultative endosymbiosis between Paramecium bursaria and Chlorella spp., we demonstrate that this mechanism is dependent on the host RNA-interference (RNAi) system. We reveal through small RNA (sRNA) sequencing that endosymbiont-derived messenger RNA (mRNA) released upon endosymbiont digestion can be processed by the host RNAi system into 23-nt sRNA. We predict multiple regions of shared sequence identity between endosymbiont and host mRNA, and demonstrate through delivery of synthetic endosymbiont sRNA that exposure to these regions can knock down expression of complementary host genes, resulting in a cost to host growth. This process of host gene knockdown in response to endosymbiont-derived RNA processing by host RNAi factors, which we term “RNAi collisions,” represents a mechanism that can promote stability in a facultative eukaryote–eukaryote endosymbiosis. Specifically, by imposing a cost for breakdown of the endosymbiosis, endosymbiont–host RNA–RNA interactions may drive maintenance of the symbiosis across fluctuating ecological conditions.

Microbiota Diversity of Festuca Sinensis Seeds in Different Location of Qinghai-Tibet Plateau

Background: The Qinghai-Tibet Plateau is characterized by strong ultraviolet rays, extended sunshine durations, high altitudes, substantial temperature differences between day and night, dry air, and poor soil water and fertilizer preservation ability[54]. Although the environment and climatic conditions of the Qinghai-Tibet Plateau and growth conditions of plants are well known, relatively few studies have been conducted on the effects of environmental factors on seed microbiota diversity on the Qinghai-Tibet Plateau. Festuca sinensis is a cool-season perennial grass species suitable for growth on the Qinghai-Tibet Plateau. Therefore, investigating the Festuca sinensis seed microflora diversity could play an important role in establishing plant species diversity on the Qinghai-Tibet Plateau. Results: Festuca sinensis seeds were collected from 14 locations on the Qinghai-Tibet Plateau, and their endophyte status and seed microflora were analyzed to determine the effects of endophytes and host growth environment on the microflora of F. sinensis seeds. The results showed that the endophyte infection rate of these germplasms ranged from 0% to 80%. Endophyte infection rates were significantly negatively correlated with elevation(P<0.05)and significantly positively correlated with monthly mean temperature (MMT)(P<0.05)and growing monthly mean temperature (GMMT)(P<0.01). Microflora analysis using high-throughput sequencing showed that Proteobacteria, Cyanobacteria, and Bacteroidetes were the most abundant bacteria at the phylum level, and Ascomycota and Basidiomycota were the most abundant fungi at the phylum level in seeds. Regarding the relative abundance of each phylum in different seed lots, significant differences occurred among the 14 ecotypes. Bacterial and fungal diversity indices, including Chao1, Shannon, Simpson, and Adaptive Communication Environment (ACE), showed significant differences among these 14 ecotypes, although they were not consistent among the indices. These diversity indices were correlated with the host growth environment. For example, the Chao richness and ACE indices of bacteria were significantly negatively correlated with monthly mean precipitation, annual mean precipitation, and growing monthly mean precipitation(P<0.05). The Chao richness index of fungi was significantly negatively correlated with MMT, annual mean temperature (AMT), and GMMT (P<0.05). The ACE index of fungi was significantly negatively correlated with MMT, AMT, and GMT(P<0.01). The relative abundance (ACE index) of fungi was significantly positively correlated with elevation. The Chao richness index of fungi was significantly negatively correlated with MMT, AMT, and GMMT.Conclusions: These results suggest that average precipitation had significant effects on the abundance of bacteria, whereas the endophyte infection rate, elevation, and average temperature significantly affected the abundance of fungi. Temperature and elevation had significant effects on the endophyte infection rate.