Mucinivorans hirudinis gen. nov., sp. nov., an anaerobic, mucin-degrading bacterium isolated from the digestive tract of the medicinal leech Hirudo verbana

Genetic Variation and Gene Expression of the Antimicrobial Peptide Macins in Asian Buffalo Leech (Hirudinaria manillensis)

With the growing severity of antibiotic resistance, antimicrobial peptides demonstrate significant potential for medical applications. Here, we performed genome and transcriptome sequencing of 30 Asian buffalo leech (Hirudinaria manillensis) individuals and integrated data from three other leech species (Whitmania pigra, Hirudo nipponia, and Hirudo medicinalis) to investigate genetic variation and gene expression of H. manillensis macins. Three macins (Hman1, Hman2, and Hman3), along with their encoding genes (Hman1, Hman2, and Hman3), were identified in H. manillensis. Hman1 exhibited the highest similarity (63.5 ± 12.0%) to macins from other leeches, followed by Hman2 (57.8 ± 7.4%) and Hman3 (30.0 ± 3.5%). Both amino acid and codon sequences of Hman1 were conserved within the species, whereas Hman2 and Hman3 exhibited markedly higher variability. All Hman1 sequences were translatable, while four Hman2 and 28 Hman3 sequences had degenerated into pseudogenes. Transcripts per million (TPM) values for Hman1, Hman2, and Hman3 were 2196.63, 242.35, and 1.22, respectively. Total macin expression in H. manillensis was less than 1/20 of that in W. pigra. Based on sequence variation and expression patterns, we propose that Hman1 retains functionality while Hman2 and Hman3 have lost or are losing their antibacterial functions.

Hirudo verbana Microbiota Dynamics: A Key Factor in Hirudotherapy-Related Infections?

The gastrointestinal microbiota of medicinal leeches is particularly interesting due to their blood-feeding habits, increasing medical use, and risk of pathogen transmission. Three groups of Hirudo verbana were used to study the leech microbiota: farmed leeches fasting for a long time, farmed leeches recently fed with bovine blood, and wild specimens fed with amphibian blood. The microbiota of the leeches' mouth, pharynx, crop, and intestine was analyzed. Metasequencing analyses were performed using amplification of the 16S rRNA V3-V4 region on a NovaSeq Illumina platform. The relative abundance of bacterial microbiota included environmental bacteria from the families Rhizobiaceae, Comamonadaceae, Sphingobacteriaceae, Phreatobacteraceae, Myxococcaceae, Chitinophagaceae, Rhodospirillaceae, and Bdellovibrionaceae, as well as symbiotic/probiotic bacteria such as Mucinivorans, Aeromonas, Vagococcus, Lactobacillales, and Morganella. Significant differences were found in the different regions of the digestive system among the three groups of leeches, and environmental bacteria were present in all groups to varying degrees. A negative correlation was found between the dominant environmental and the symbiotic/probiotic bacteria. In contrast, a positive correlation was found between environmental and symbiotic/probiotic bacteria, indicating their association with host factors. Microbiota diversity, abundance, and bacterial correlations may be influenced by factors such as the leech's fasting state, blood meal source, and environmental conditions. The identified opportunistic pathogens, such as Rickettsia, Anaplasma, and Treponema, identified for the first time in H. verbana, should be taken into consideration when using this leech in hirudotherapy. Our results show that extensive screening for opportunistic and pathogenic agents should be performed on leeches intended for medical use. Long-fasting leeches and leeches cultured in specialized farms are recommended for hirudotherapy.

Cross-species gut microbiota transplantation predictably affects host heat tolerance

The gut microbiome is known to influence and have regulatory effects in diverse physiological functions of host animals, but only recently has the relationship between host thermal biology and gut microbiota been explored. Here, we examined how early-life manipulations of the gut microbiota in larval amphibians influenced their critical thermal maximum (CTmax) at different acclimation temperatures. We stripped the resident microbiome from egg masses of wild-caught wood frogs (Lithobates sylvaticus) via an antibiotic wash, and then inoculated the eggs with pond water (control), no inoculation, or the intestinal microbiota of another species that has a wider thermal tolerance - green frogs (Lithobates clamitans). We predicted that this cross-species transplant would increase the CTmax of the recipient wood frog larvae relative to the other treatments. In line with this prediction, green frog microbiome-recipient larvae had the highest CTmax while those with no inoculum had the lowest CTmax. Both the microbiome treatment and acclimation temperature significantly influenced the larval gut microbiota communities and α-diversity indices. Green frog microbiome-inoculated larvae were enriched in Rikenellaceae relative to the other treatments, which produce short-chain fatty acids and could contribute to greater energy availability and enhanced heat tolerance. Larvae that received no inoculation had a higher relative abundance of potentially pathogenic Aeromonas spp., which negatively affects host health and performance. Our results are the first to show that cross-species gut microbiota transplants alter heat tolerance in a predictable manner. This finding has repercussions for the conservation of species that are threatened by climate change and demonstrates a need to further explore the mechanisms by which the gut microbiota modulate host thermal tolerance.

Marine vampires: Persistent, internal associations between bacteria and blood-feeding marine annelids and crustaceans

Persistent bacterial presence is believed to play an important role in host adaptation to specific niches that would otherwise be unavailable, including the exclusive consumption of blood by invertebrate parasites. Nearly all blood-feeding animals examined so far host internal bacterial symbionts that aid in some essential aspect of their nutrition. Obligate blood-feeding (OBF) invertebrates exist in the oceans, yet symbiotic associations between them and beneficial bacteria have not yet been explored. This study describes the microbiome of 6 phylogenetically-diverse species of marine obligate blood-feeders, including leeches (both fish and elasmobranch specialists; e.g., Pterobdella, Ostreobdella, and Branchellion), isopods (e.g., Elthusa and Nerocila), and a copepod (e.g., Lernanthropus). Amplicon sequencing analysis revealed the blood-feeding invertebrate microbiomes to be low in diversity, compared to host fish skin surfaces, seawater, and non-blood-feeding relatives, and dominated by only a few bacterial genera, including Vibrio (100% prevalence and comprising 39%-81% of the average total recovered 16S rRNA gene sequences per OBF taxa). Vibrio cells were localized to the digestive lumen in and among the blood meal for all taxa examined via fluorescence microscopy. For Elthusa and Branchellion, Vibrio cells also appeared intracellularly within possible hemocytes, suggesting an interaction with the immune system. Additionally, Vibrio cultivated from four of the obligate blood-feeding marine taxa matched the dominant amplicons recovered, and all but one was able to effectively lyse vertebrate blood cells. Bacteria from 2 additional phyla and 3 families were also regularly recovered, albeit in much lower abundances, including members of the Oceanospirillaceae, Flavobacteriacea, Porticoccaceae, and unidentified members of the gamma-and betaproteobacteria, depending on the invertebrate host. For the leech Pterobdella, the Oceanospirillaceae were also detected in the esophageal diverticula. For two crustacean taxa, Elthusa and Lernanthropus, the microbial communities associated with brooded eggs were very similar to the adults, indicating possible direct transmission. Virtually nothing is known about the influence of internal bacteria on the success of marine blood-feeders, but this evidence suggests their regular presence in marine parasites from several prominent groups.

Roadmap from Microbial Communities to Individuality Modeling for Anaerobic Digestion of Sewage Sludge

Biological models describing anaerobic digestion (AD) of sewage sludge have been widely applied to test various control and operation strategies. Anaerobic digestion model 1 (ADM1) provides a generic platform that includes the main processes of AD, excluding homoacetogenesis and the microbial structure. Homoacetogenic bacteria have been identified as important competitors for hydrogen consumption and acetate production. Although recent advances in meta-omics techniques have improved our characterization of AD microbial communities, conventional models treat functional groups as homogeneous and overlook the physiology and behavior of microbial individuality, limiting insights into mechanisms governing process performance. A novel microbial individuality model (MIM) that integrates kinetics, energetics, and agent-based modeling to describe a microbiome's behavior as heterogenic populations, including homoacetogenesis, was developed. The MIM was validated with two datasets from previous studies through daily biogas production, methane content, compound concentrations, and microbial relative abundance changes. The MIM identified the emergence of Methanosaeta at low concentrations of acetate. Moreover, this simulation supports experimental studies confirming that the overlooked homoacetogenesis is an important hydrogen sink in AD. Validated MIMs are expected to provide insights into syntrophic and competitive interactions among microbiomes in AD systems while testing different operational parameters in a virtual environment. The MIM offers a methodological framework to other biological treatment systems and their microbial community dynamics.

A mucin protein predominantly expressed in the female-specific symbiotic organ of the stinkbug Plautia stali

Diverse insects are obligatorily associated with microbial symbionts, wherein the host often develops special symbiotic organs and vertically transmits the symbiont to the next generation. What molecular factors underpin the host-symbiont relationship is of great interest but poorly understood. Here we report a novel protein preferentially produced in a female-specific symbiotic organ of the stinkbug Plautia stali, whose posterior midgut develops numerous crypts to host a Pantoea-allied bacterial mutualist. In adult females, several posteriormost crypts are conspicuously enlarged, presumably specialized for vertical symbiont transmission. We detected conspicuous protein bands specific to the female’s swollen crypts by gel electrophoresis, and identified them as representing a novel mucin-like glycoprotein. Histological inspections confirmed that the mucin protein is localized to the female’s swollen crypts, coexisting with a substantial population of the symbiotic bacteria, and excreted from the swollen crypts to the midgut main tract together with the symbiotic bacteria. Using RNA interference, we successfully suppressed production of the mucin protein in adult females of P. stali. However, although the mucin protein was depleted, the symbiont population persisted in the swollen crypts, and vertical symbiont transmission to the next generation occurred. Possible biological roles and evolutionary trajectory of the symbiosis-related mucin protein are discussed.

The capture technology matters: Composition of municipal wastewater solids drives complexity of microbial community structure and volatile fatty acid profile during anaerobic fermentation

The production of volatile fatty acids (VFAs) represents a relevant option to valorize municipal wastewater (MWW). In this context, different capture technologies can be used to recover organic carbon from wastewater in form of solids, while pre-treatment of those solids has the potential to increase VFA production during subsequent fermentation. Our study investigates how VFA composition produced by fermentation is influenced (i) by the choice of the capture technology, as well as (ii) by the use of thermal alkaline pre-treatment (TAP). Therefore, the fermentation of solids originating from a primary settler, a micro-sieve, and a high-rate activated sludge (HRAS) system was investigated in continuous lab-scale fermenters, with and without TAP. Our study demonstrates that the capture technology strongly influences the composition of the produced solids, which in turn drives the complexity of the fermenter's microbial community and ultimately, of the VFA composition. Solids captured with the primary settler or micro-sieve consisted primarily of polysaccharides, and led to the establishment of a microbial community specialized in the degradation of complex carbohydrates. The produced VFA composition was relatively simple, with acetate and propionate accounting for >90% of the VFAs. In contrast, the HRAS system produced biomass-rich solids associated with higher protein contents. The microbial community which then developed in the fermenter was therefore more diversified and capable of converting a wider range of substrates (polysaccharides, proteins, amino acids). Ultimately, the produced VFA composition was more complex, with equal fractions of isoacids and propionate (both ~20%), while acetate remained the dominant acid (~50%). Finally, TAP did not significantly modify the VFA composition while increasing VFA yields on HRAS and sieved material by 35% and 20%, respectively. Overall, we demonstrated that the selection of the technology used to capture organic substrates from MWW governs the composition of the VFA cocktail, ultimately with implications for their further utilization.

Insights into gut microbiota communities of Poecilobdella manillensis, a prevalent Asian medicinal leech

AIMS

Medicinal leeches (Annelida: Hirudinea) are fresh water ectoparasitic species which have been applied as traditional therapy. However, gut microbiota could bring high risks of opportunistic infections after leeching, and arouses great interests. Here gut bacterial and fungal communities of an Asian prevalent leech Poecilobdella manillensis, were characterized and analyzed through culture-independent sequencing.

METHODS AND RESULTS

With high coverage in 18 samples (>0.999), a more complicated community was apparent after comparing with previous leech studies. A total of 779/939 OTUs of bacteria and fungi were detected from leech guts. The bacterial community was dominated by phylum Bacteroidetes and Synergistetes. Genera Mucinivorans and Fretibacterium accounted mostly at the genus level. And genus Aeromonas showed an extremely low abundance (2.02%) on average. The fungal community was dominated by phylum Ascomycota and Basidiomycota. At the genus level, the dominant OTUs included Mortierella, Geminibasidium and Fusarium. The analysis of core taxa included those above dominant genera and some low-abundance genera (>1%). The functional annotation of bacterial community showed a close correlation with metabolism (34.8 ± 0.6%). Some fungal species were predicted as opportunistic human pathogens including Fusarium and Chaetomiaceae.

CONCLUSIONS

The present study provides fundamental rationales for further studies of such issues as bacteria-fungi-host interactions, host fitness, potential pathogens and infecting risks after leeching. It shall facilitate in-depth explorations on a safe utilization of leech therapy.

SIGNIFICANCE AND IMPACT OF STUDY

Present paper is the first-ever exploration on microbiota of a prevalent Asian medicinal leech based on culture-independent technical. And it is also the first report of gut fungi community of medicinal leech. The diversity and composition of bacteria in P. manillensis was far different from that of the European leech. The main components and core OTUs indicate a particular gut environment of medicinal leech. Unknown bacterial and fungal species were also recovered from leech gut.

Excess iron supplementation induced hepatopancreas lipolysis, destroyed intestinal function in Pacific white shrimp Litopenaeus vannamei

So far, the adverse effects of excess Fe in shrimp have been ignored for years as it was thought that extra Fe supplementation was not needed in the practical diets. Nowadays, Fe concentration in commercial shrimp feed from feed enterprises could be around 301.34-545.5 mg/kg, which is mainly due to the fish meal containing up to 1500 mg/kg Fe. Therefore, the purpose of this experiment was to investigate the effects of Fe supplementation on the growth performance, tissue Fe deposition, hepatopancreas lipid metabolism, intestinal function in L. vannamei. The results showed that although growth performance was not influenced by the dietary Fe supplementation, excess Fe supplementation (955.00 mg/kg) significantly increased hepatopancreas Fe deposition and induced lipolysis. Moreover, excess Fe supplementation impaired intestinal immune function and disrupted microbiota homeostasis. These findings might provide partial theoretical evidence for the effect of dietary Fe supplementation on physiological metabolism in L. vannamei.

Macrobdella decora: Old World Leech Gut Microbial Community Structure Conserved in a New World Leech

Leeches are found in terrestrial, aquatic, and marine habitats on all continents. Sanguivorous leeches have been used in medicine for millennia. Modern scientific uses include studies of neurons, anticoagulants, and gut microbial symbioses. Hirudo verbana, the European medicinal leech, maintains a gut community dominated by two bacterial symbionts, Aeromonas veronii and Mucinivorans hirudinis, which sometimes account for as much as 97% of the total crop microbiota. The highly simplified gut anatomy and microbiome of H. verbana make it an excellent model organism for studying gut microbial dynamics. The North American medicinal leech, Macrobdella decora, is a hirudinid leech native to Canada and the northern United States. In this study, we show that M. decora symbiont communities are very similar to those in H. verbana. We performed an extensive study using field-caught M. decora and purchased H. verbana from two suppliers. Deep sequencing of the V4 region of the 16S rRNA gene allowed us to determine that the core microbiome of M. decora consists of Bacteroides, Aeromonas, Proteocatella, and Butyricicoccus. The analysis revealed that the compositions of the gut microbiomes of the two leech species were significantly different at all taxonomic levels. The R ² value was highest at the genus and amplicon sequence variant (ASV) levels and much lower at the phylum, class, and order levels. The gut and bladder microbial communities were distinct. We propose that M. decora is an alternative to H. verbana for studies of wild-caught animals and provide evidence for the conservation of digestive-tract and bladder symbionts in annelid models.IMPORTANCE Building evidence implicates the gut microbiome in critical animal functions such as regulating digestion, nutrition, immune regulation, and development. Simplified, phylogenetically diverse models for hypothesis testing are necessary because of the difficulty of assigning causative relationships in complex gut microbiomes. Previous research used Hirudo verbana as a tractable animal model of digestive-tract symbioses. Our data show that Macrobdella decora may work just as well without the drawback of being an endangered organism and with the added advantage of easy access to field-caught specimens. The similarity of the microbial community structures of species from two different continents reveals the highly conserved nature of the microbial symbionts in sanguivorous leeches.

Multiple-cycle operation of sulphur-cycle-enhanced biological phosphorus removal to maintain stable performance at high temperatures

This study investigated a new method of multiple-cycle operation of a sulphur-cycle-enhanced biological phosphorus (P) removal system to maintain good phosphorus removal performance at a high temperature (30 °C). The findings demonstrate that P removal was low and unstable under a normal cycle (77 ± 18%), but multiple cycles resulted in a high and quite stable level of P removal (88 ± 9%). Moreover, in the normal mode, the polyhydroxyalkanoate levels increased significantly from 2 to 15 mg C/g of VSS, the glycogen level doubled from 5 to 10 mg C/g of VSS and the polyhydroxyalkanoate and glycogen levels were maintained at considerably low levels after multiple cycles (only 5 C/g of VSS). The 16S rRNA high-throughput sequencing analysis revealed that the genera Thioalbus and Psychrobacter in the gamma-Proteobacteria class were the key functional communities. These findings suggest a high level of P removal with multiple cycles of sulphur-cycle enhanced biological phosphorus removal.

Bacterial Community of the Digestive Tract of the European Medicinal Leech (Hirudo verbana) from the Danube River

The digestive tract of medicinal leeches from commercial suppliers has been investigated previously and comprises of a relatively simple bacterial community. However, the microbiome of medicinal leeches collected directly from the natural habitat has not been examined. In this study, we characterized the bacterial community in the digestive tract (anterior crop, posterior crop, and intestine) of the European medicinal leech, Hirudo verbana, collected from the Danube river using culture-independent and culture-dependent approaches. Culture-independent approach confirmed that the digestive tract of H. verbana carries a relatively simple bacterial community with species richness in the individual samples ranging from 43 to164. The dominant bacterial taxon was Mucinivorans sp. (49.7% of total reads), followed by Aeromonas sp. (18.7% of total reads). Several low abundance taxa, new for H. verbana, such as Phreatobacter, Taibaiella, Fluviicola, Aquabacterium, Burkholderia, Hydrogenophaga, Wolinella, and unidentified Chitinophagia, were also detected. The aerobic culturing approach showed Aeromonas veronii (Proteobacteria), the known leech symbiont, as the most dominant taxon followed by several Pseudomonas and Acidovorax spp. No significant differences in the bacterial community composition were detected among different parts of the digestive tract of individual leeches. However, the overall composition of the bacterial community among individual specimen varied significantly and this is possibly due to differences in leech age, feeding status, and blood source. Our results showed that the core bacterial community of H. verbana collected from the natural habitat is similar to that reported from the digestive tract of commercially supplied leeches maintained in the laboratory.

FunctionAnnotator, a versatile and efficient web tool for non-model organism annotation

Along with the constant improvement in high-throughput sequencing technology, an increasing number of transcriptome sequencing projects are carried out in organisms without decoded genome information and even on environmental biological samples. To study the biological functions of novel transcripts, the very first task is to identify their potential functions. We present a web-based annotation tool, FunctionAnnotator, which offers comprehensive annotations, including GO term assignment, enzyme annotation, domain/motif identification and predictions for subcellular localization. To accelerate the annotation process, we have optimized the computation processes and used parallel computing for all annotation steps. Moreover, FunctionAnnotator is designed to be versatile, and it generates a variety of useful outputs for facilitating other analyses. Here, we demonstrate how FunctionAnnotator can be helpful in annotating non-model organisms. We further illustrate that FunctionAnnotator can estimate the taxonomic composition of environmental samples and assist in the identification of novel proteins by combining RNA-Seq data with proteomics technology. In summary, FunctionAnnotator can efficiently annotate transcriptomes and greatly benefits studies focusing on non-model organisms or metatranscriptomes. FunctionAnnotator, a comprehensive annotation web-service tool, is freely available online at: http://fa.cgu.edu.tw/. This new web-based annotator will shed light on field studies involving organisms without a reference genome.

The Social Life of Aeromonas through Biofilm and Quorum Sensing Systems

Bacteria of the genus Aeromonas display multicellular behaviors herein referred to as “social life”. Since the 1990s, interest has grown in cell-to-cell communication through quorum sensing signals and biofilm formation. As they are interconnected, these two self-organizing systems deserve to be considered together for a fresh perspective on the natural history and lifestyles of aeromonads. In this review, we focus on the multicellular behaviors of Aeromonas, i.e., its social life. First, we review and discuss the available knowledge at the molecular and cellular levels for biofilm and quorum sensing. We then discuss the complex, subtle, and nested interconnections between the two systems. Finally, we focus on the aeromonad multicellular coordinated behaviors involved in heterotrophy and virulence that represent technological opportunities and applied research challenges.

Host Matters: Medicinal Leech Digestive-Tract Symbionts and Their Pathogenic Potential

Digestive-tract microbiota exert tremendous influence over host health. Host-symbiont model systems are studied to investigate how symbioses are initiated and maintained, as well as to identify host processes affected by resident microbiota. The medicinal leech, Hirudo verbana, is an excellent model to address such questions owing to a microbiome that is consistently dominated by two species, Aeromonas veronii and Mucinivorans hirudinis, both of which are cultivable and have sequenced genomes. This review outlines current knowledge about the dynamics of the H. verbana microbiome. We discuss in depth the factors required for A. veronii colonization and proliferation in the leech crop and summarize the current understanding of interactions between A. veronii and its annelid host. Lastly, we discuss leech usage in modern medicine and highlight how leech-therapy associated infections, often attributable to Aeromonas spp., are of growing clinical concern due in part to an increased prevalence of fluoroquinolone resistant strains.

Description of Ancylomarina subtilis gen. nov., sp. nov., isolated from coastal sediment, proposal of Marinilabiliales ord. nov. and transfer of Marinilabiliaceae, Prolixibacteraceae and Marinifilaceae to the order Marinilabiliales

A Gram-stain-negative, facultatively anaerobic, moderately halophilic, filamentous, non-motile bacterium, designated FA102T, was isolated from marine sediment from the coast of Weihai, PR China. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain FA102T formed a distinct evolutionary lineage within the family Marinifilaceae and its closest relative was Marinifilum fragile JCM 15579T (93.2 % sequence similarity). The DNA G+C content of the novel strain was 36.5 mol%. The predominant cellular fatty acids and respiratory quinone were iso-C15 : 0 and iso-C15 : 0 3-OH, and MK-7, respectively. On the basis of the phylogenetic, phenotypic and physiological data, strain FA102T represents a novel genus and species, for which the name Ancylomarina subtilis gen. nov., sp. nov. is proposed. The type strain of Ancylomarina subtilis is FA102T (=KCTC 42257T=DSM 28825T=CICC 10902T). Furthermore, a new order named Marinilabiliales is proposed to accommodate three families previously classified in the order Bacteroidales. Marinilabiliales ord. nov. encompasses the families Marinilabiliaceae, Prolixibacteraceae and Marinifilaceae.

Lessons from Digestive-Tract Symbioses Between Bacteria and Invertebrates

In most animals, digestive tracts harbor the greatest number of bacteria in the animal that contribute to its health: by aiding in the digestion of nutrients, provisioning essential nutrients and protecting against colonization by pathogens. Invertebrates have been used to enhance our understanding of metabolic processes and microbe-host interactions owing to experimental advantages. This review describes how advances in DNA sequencing technologies have dramatically altered how researchers investigate microbe-host interactions, including 16S rRNA gene surveys, metagenome experiments, and metatranscriptome studies. Advantages and challenges of each of these approaches are described herein. Hypotheses generated through omics studies can be directly tested using site-directed mutagenesis, and findings from transposon studies and site-directed experiments are presented. Finally, unique structural aspects of invertebrate digestive tracts that contribute to symbiont specificity are presented. The combination of omics approaches with genetics and microscopy allows researchers to move beyond correlations to identify conserved mechanisms of microbe-host interactions.

A Tale of Transmission: Aeromonas veronii Activity within Leech-Exuded Mucus

Transmission, critical to the establishment and persistence of host-associated microbiotas, also exposes symbionts to new environmental conditions. With horizontal transmission, these different conditions represent major lifestyle shifts. Yet genome-wide analyses of how microbes adjust their transcriptomes toward these dramatic shifts remain understudied. Here, we provide a comprehensive and comparative analysis of the global transcriptional profiles of a symbiont as it shifts between lifestyles during transmission. The gammaproteobacterium Aeromonas veronii is transmitted from the gut of the medicinal leech to other hosts via host mucosal castings, yet A. veronii can also transition from mucosal habitancy to a free-living lifestyle. These three lifestyles are characterized by distinct physiological constraints and consequently lifestyle-specific changes in the expression of stress-response genes. Mucus-bound A. veronii had the greatest expression in terms of both the number of loci and levels of transcription of stress-response mechanisms. However, these bacteria are still capable of proliferating within the mucus, suggesting the availability of nutrients within this environment. We found that A. veronii alters transcription of loci in a synthetic pathway that obtains and incorporates N-acetylglucosamine (NAG; a major component of mucus) into the bacterial cell wall, enabling proliferation. Our results demonstrate that symbionts undergo dramatic local adaptation, demonstrated by widespread transcriptional changes, throughout the process of transmission that allows them to thrive while they encounter new environments which further shape their ecology and evolution.

Solving a Bloody Mess: B-Vitamin Independent Metabolic Convergence among Gammaproteobacterial Obligate Endosymbionts from Blood-Feeding Arthropods and the Leech Haementeria officinalis

Endosymbiosis is a common phenomenon in nature, especially between bacteria and insects, whose typically unbalanced diets are usually complemented by their obligate endosymbionts. While much interest and focus has been directed toward phloem-feeders like aphids and mealybugs, blood-feeders such as the Lone star tick (Amblyomma americanum), Glossina flies, and the human body louse (Pediculus humanus corporis) depend on obligate endosymbionts which complement their B-vitamin-deficient diets, and thus are required for growth and survival. Glossiphoniid leeches have also been found to harbor distinct endosymbionts housed in specialized organs. Here, we present the genome of the bacterial endosymbiont from Haementeria officinalis, first of a glossiphoniid leech. This as-yet-unnamed endosymbiont belongs to the Gammaproteobacteria, has a pleomorphic shape and is restricted to bacteriocytes. For this bacterial endosymbiont, we propose the name Candidatus Providencia siddallii. This symbiont possesses a highly reduced genome with high A+T content and a reduced set of metabolic capabilities, all of which are common characteristics of ancient obligate endosymbionts of arthropods. Its genome has retained many pathways related to the biosynthesis of B-vitamins, pointing toward a role in supplementing the blood-restricted diet of its host. Through comparative genomics against the endosymbionts of A. americanum, Glossina flies, and P. humanus corporis, we were able to detect a high degree of metabolic convergence among these four very distantly related endosymbiotic bacteria.

Complete Genome Sequence of the Novel Leech Symbiont Mucinivorans hirudinis M3T

Mucinivorans hirudinis M3(T) was isolated from the digestive tract of the medicinal leech, Hirudo verbana, and is the type species of a new genus within the Rikenellaceae. Here, we report the complete annotated genome sequence of this bacterium.