Transmission and dynamics of mother-infant gut viruses during pregnancy and early life

Early development of the gut ecosystem is crucial for lifelong health. While infant gut bacterial communities have been studied extensively, the infant gut virome remains under-explored. To study the development of the infant gut virome over time and the factors that shape it, we longitudinally assess the composition of gut viruses and their bacterial hosts in 30 women during and after pregnancy and in their 32 infants during their first year of life. Using shotgun metagenomic sequencing applied to dsDNA extracted from Virus-Like Particles (VLPs) and bacteria, we generate 205 VLP metaviromes and 322 total metagenomes. With this data, we show that while the maternal gut virome composition remains stable during late pregnancy and after birth, the infant gut virome is dynamic in the first year of life. Notably, infant gut viromes contain a higher abundance of active temperate phages compared to maternal gut viromes, which decreases over the first year of life. Moreover, we show that the feeding mode and place of delivery influence the gut virome composition of infants. Lastly, we provide evidence of co-transmission of viral and bacterial strains from mothers to infants, demonstrating that infants acquire some of their virome from their mother's gut.

Dynamic nature of viral and bacterial communities in human faeces

Bacteriophages are a major component of the gut microbiome and are believed to play a role in establishment and stabilization of microbial communities by influencing taxonomic and functional diversity. We show that the activity of lytic and temperate phages can also significantly affect bacterial community structure in a model of extended colonic retention. Intact fresh human feces were incubated anaerobically at 37°C without homogenization and subjected to metagenomic sequencing. We observed subject-specific blooms and collapses of selected bacteriophage and bacterial populations within some individuals. Most notable were striking collapses of Prevotella populations accompanied by increases in specific bacteriophages. In a number of cases, we even observed a shift from one bacterial "enterotype" to another within 48 h. These results confirm that intact feces represents a highly dynamic ecological system and suggests that colonic retention time could have a profound effect on microbiome composition, including a significant impact by bacteriophages.

The gut virome is associated with stress-induced changes in behaviour and immune responses in mice

The microbiota-gut-brain axis has been shown to play an important role in the stress response, but previous work has focused primarily on the role of the bacteriome. The gut virome constitutes a major portion of the microbiome, with bacteriophages having the potential to remodel bacteriome structure and activity. Here we use a mouse model of chronic social stress, and employ 16S rRNA and whole metagenomic sequencing on faecal pellets to determine how the virome is modulated by and contributes to the effects of stress. We found that chronic stress led to behavioural, immune and bacteriome alterations in mice that were associated with changes in the bacteriophage class Caudoviricetes and unassigned viral taxa. To determine whether these changes were causally related to stress-associated behavioural or physiological outcomes, we conducted a faecal virome transplant from mice before stress and autochthonously transferred it to mice undergoing chronic social stress. The transfer of the faecal virome protected against stress-associated behaviour sequelae and restored stress-induced changes in select circulating immune cell populations, cytokine release, bacteriome alterations and gene expression in the amygdala. These data provide evidence that the virome plays a role in the modulation of the microbiota-gut-brain axis during stress, indicating that these viral populations should be considered when designing future microbiome-directed therapies.

Social anxiety disorder-associated gut microbiota increases social fear

Social anxiety disorder (SAD) is a crippling psychiatric disorder characterized by intense fear or anxiety in social situations and their avoidance. However, the underlying biology of SAD is unclear and better treatments are needed. Recently, the gut microbiota has emerged as a key regulator of both brain and behaviour, especially those related to social function. Moreover, increasing data supports a role for immune function and oxytocin signalling in social responses. To investigate whether the gut microbiota plays a causal role in modulating behaviours relevant to SAD, we transplanted the microbiota from SAD patients, which was identified by 16S rRNA sequencing to be of a differential composition compared to healthy controls, to mice. Although the mice that received the SAD microbiota had normal behaviours across a battery of tests designed to assess depression and general anxiety-like behaviours, they had a specific heightened sensitivity to social fear, a model of SAD. This distinct heightened social fear response was coupled with changes in central and peripheral immune function and oxytocin expression in the bed nucleus of the stria terminalis. This work demonstrates an interkingdom basis for social fear responses and posits the microbiome as a potential therapeutic target for SAD.

Isolation and characterization of a novel lytic Parabacteroides distasonis bacteriophage φPDS1 from the human gut

The human gut microbiome plays a significant role in health and disease. The viral component (virome) is predominantly composed of bacteriophages (phages) and has received significantly less attention in comparison to the bacteriome. This knowledge gap is largely due to challenges associated with the isolation and characterization of novel gut phages, and bioinformatic hurdles such as the lack of a universal phage marker gene and the absence of sufficient numbers of homologs in viral databases. Here, we describe the isolation from human feces of a novel lytic phage with siphovirus morphology, φPDS1, infecting Parabacteroides distasonis APCS2/PD, and classified within a newly proposed Sagittacolavirus genus. In silico and biological characterization of this phage is presented in this study. Key to the isolation of φPDS1 was the antibiotic-driven selective enrichment of the bacterial host in a fecal fermenter. Despite producing plaques and lacking genes associated with lysogeny, φPDS1 demonstrates the ability to coexist in liquid culture for multiple days without affecting the abundance of its host. Multiple studies have shown that changes in Parabacteroides distasonis abundance can be linked to various disease states, rendering this novel phage-host pair and their interactions of particular interest.

Factors Affecting Variation of the Human Gut Phageome

The gut microbiome is a dense and metabolically active consortium of microorganisms and viruses located in the lower gastrointestinal tract of the human body. Bacteria and their viruses (phages) are the most abundant members of the gut microbiome. Investigating their biology and the interplay between the two is important if we are to understand their roles in human health and disease. In this review, we summarize recent advances in resolving the taxonomic structure and ecological functions of the complex community of phages in the human gut-the gut phageome. We discuss how age, diet, and geography can all have a significant impact on phageome composition. We note that alterations to the gut phageome have been observed in several diseases such as inflammatory bowel disease, irritable bowel syndrome, and colorectal cancer, and we evaluate whether these phageome changes can directly or indirectly contribute to disease etiology and pathogenesis. We also highlight how lack of standardization in studying the gut phageome has contributed to variation in reported results.

Structural atlas of a human gut crassvirus

CrAssphage and related viruses of the order Crassvirales (hereafter referred to as crassviruses) were originally discovered by cross-assembly of metagenomic sequences. They are the most abundant viruses in the human gut, are found in the majority of individual gut viromes, and account for up to 95% of the viral sequences in some individuals1-4. Crassviruses are likely to have major roles in shaping the composition and functionality of the human microbiome, but the structures and roles of most of the virally encoded proteins are unknown, with only generic predictions resulting from bioinformatic analyses4,5. Here we present a cryo-electron microscopy reconstruction of Bacteroides intestinalis virus ΦcrAss0016, providing the structural basis for the functional assignment of most of its virion proteins. The muzzle protein forms an assembly about 1 MDa in size at the end of the tail and exhibits a previously unknown fold that we designate the 'crass fold', that is likely to serve as a gatekeeper that controls the ejection of cargos. In addition to packing the approximately 103 kb of virus DNA, the ΦcrAss001 virion has extensive storage space for virally encoded cargo proteins in the capsid and, unusually, within the tail. One of the cargo proteins is present in both the capsid and the tail, suggesting a general mechanism for protein ejection, which involves partial unfolding of proteins during their extrusion through the tail. These findings provide a structural basis for understanding the mechanisms of assembly and infection of these highly abundant crassviruses.

Draft Genome Sequence of Legionella pneumophila subsp. pneumophila Strain DSM 25199

Here, we report the 3,426,844-bp draft genome sequence of Legionella pneumophila subsp. pneumophila strain DSM 25199, a serogroup 1 strain of L. pneumophila. The assembly consists of 24 contigs with an N₅₀ of 300,843 bp.

Bacteriophages of the Order Crassvirales: What Do We Currently Know about This Keystone Component of the Human Gut Virome?

The order Crassvirales comprises dsDNA bacteriophages infecting bacteria in the phylum Bacteroidetes that are found in a variety of environments but are especially prevalent in the mammalian gut. This review summarises available information on the genomics, diversity, taxonomy, and ecology of this largely uncultured viral taxon. With experimental data available from a handful of cultured representatives, the review highlights key properties of virion morphology, infection, gene expression and replication processes, and phage-host dynamics.

Interpersonal variability of the human gut virome confounds disease signal detection in IBD

Viruses are increasingly recognised as important components of the human microbiome, fulfilling numerous ecological roles including bacterial predation, immune stimulation, genetic diversification, horizontal gene transfer, microbial interactions, and augmentation of metabolic functions. However, our current view of the human gut virome is tainted by previous sequencing requirements that necessitated the amplification of starting nucleic acids. In this study, we performed an original longitudinal analysis of 40 healthy control, 19 Crohn's disease, and 20 ulcerative colitis viromes over three time points without an amplification bias, which revealed and highlighted the interpersonal individuality of the human gut virome. In contrast to a 16 S rRNA gene analysis of matched samples, we show that α- and β-diversity metrics of unamplified viromes are not as efficient at discerning controls from patients with inflammatory bowel disease. Additionally, we explored the intrinsic properties of unamplified gut viromes and show there is considerable interpersonal variability in viral taxa, infrequent longitudinal persistence of intrapersonal viruses, and vast fluctuations in the abundance of temporal viruses. Together, these properties of unamplified faecal viromes confound the ability to discern disease associations but significantly advance toward an unbiased and accurate representation of the human gut virome.

Abolishment of morphology-based taxa and change to binomial species names: 2022 taxonomy update of the ICTV bacterial viruses subcommittee

This article summarises the activities of the Bacterial Viruses Subcommittee of the International Committee on Taxonomy of Viruses for the period of March 2021-March 2022. We provide an overview of the new taxa proposed in 2021, approved by the Executive Committee, and ratified by vote in 2022. Significant changes to the taxonomy of bacterial viruses were introduced: the paraphyletic morphological families Podoviridae, Siphoviridae, and Myoviridae as well as the order Caudovirales were abolished, and a binomial system of nomenclature for species was established. In addition, one order, 22 families, 30 subfamilies, 321 genera, and 862 species were newly created, promoted, or moved.

Temperate bacteriophages infecting the mucin-degrading bacterium Ruminococcus gnavus from the human gut

Ruminococcus gnavus is a prevalent gut microbe reported to occur in higher abundance among individuals with inflammatory bowel disease (IBD). This study reports the isolation and characterization of six bacteriophages (phages) isolated from human fecal material and environmental samples that infect this species. Isolated phages have a siphovirus morphology, with genomes ranging between 36.5 and 37.8 kbp. Genome analysis indicates that the phages have a temperate lifestyle, which was confirmed by their ability to form lysogens on their host bacterial species. In contrast to the finding that phages lyse their host in liquid medium, results from a mouse trial indicate these phages can co-exist with the host bacterium in the gut without causing a significant reduction of R. gnavus. The bacterial counts in the feces of phage-treated mice did not significantly differ in the presence of phage. Furthermore, analysis of publicly available gut virome sequence data indicates a high abundance of these phages among individuals suffering from IBD. This work provides the first insight into how phages interact with R. gnavus in the human gut microbiome.

Mutualistic interplay between bacteriophages and bacteria in the human gut

Bacteriophages (phages) are often described as obligate predators of their bacterial hosts, and phage predation is one of the leading forces controlling the density and distribution of bacterial populations. Every 48 h half of all bacteria on Earth are killed by phages. Efficient killing also forms the basis of phage therapy in humans and animals and the use of phages as food preservatives. In turn, bacteria have a plethora of resistance systems against phage attack, but very few bacterial species, if any, have entirely escaped phage predation. However, in complex communities and environments such as the human gut, this antagonistic model of attack and counter-defence does not fully describe the scope of phage-bacterium interactions. In this Review, we explore some of the more mutualistic aspects of phage-bacterium interactions in the human gut, and we suggest that the relationship between phages and their bacterial hosts in the gut is best characterized not as a fight to the death between enemies but rather as a mutualistic relationship between partners.

Metagenomic assembled plasmids of the human microbiome vary across disease cohorts

We compiled a human metagenome assembled plasmid (MAP) database and interrogated differences across multiple studies that were originally designed to investigate the composition of the human microbiome across various lifestyles, life stages and events. This was performed as plasmids enable bacteria to rapidly expand their functional capacity through mobilisation, yet their contribution to human health and disease is poorly understood. We observed that inter-sample β-diversity differences of plasmid content (plasmidome) could distinguish cohorts across a multitude of conditions. We also show that reduced intra-sample plasmidome α-diversity is consistent amongst patients with inflammatory bowel disease (IBD) and Clostridioides difficile infections. We also show that faecal microbiota transplants can restore plasmidome diversity. Overall plasmidome diversity, specific plasmids, and plasmid-encoded functions can all potentially act as biomarkers of IBD or its severity. The human plasmidome is an overlooked facet of the microbiome and should be integrated into investigations regarding the role of the microbiome in promoting health or disease. Including MAP databases in analyses will enable a greater understanding of the roles of plasmid-encoded functions within the gut microbiome and will inform future human metagenome analyses.

Selective Isolation of Eggerthella lenta from Human Faeces and Characterisation of the Species Prophage Diversity

Eggerthella lenta is an anaerobic, high GC, Gram-positive bacillus commonly found in the human digestive tract that belongs to the class Coriobacteriia of the phylum Actinobacteria. This species has been of increasing interest as an important player in the metabolism of xenobiotics and dietary compounds. However, little is known regarding its susceptibility to bacteriophage predation and how this may influence its fitness. Here, we report the isolation of seven novel E. lenta strains using cefotaxime and ceftriaxone as selective agents. We conducted comparative and pangenome analyses of these strains and those publicly available to investigate the diversity of prophages associated with this species. Prophage gene products represent a minimum of 5.8% of the E. lenta pangenome, comprising at least ten distantly related prophage clades that display limited homology to currently known bacteriophages. All clades possess genes implicated in virion structure, lysis, lysogeny and, to a limited extent, DNA replication. Some prophages utilise tyrosine recombinases and diversity generating retroelements to generate phase variation among targeted genes. The prophages have differing levels of sensitivity to the CRISPR/cas systems of their hosts, with spacers from 44 E. lenta isolates found to target only five out of the ten identified prophage clades. Furthermore, using a PCR-based approach targeting the prophage attP site, we were able to determine that several of these elements can excise from the host chromosome, thus supporting the notion that these are active prophages. The findings of this study provide further insights into the diversity of prophages infecting species of the phylum Actinobacteria.

OUP accepted manuscript

Horizontal gene transfer (HGT) in the microbiome has profound consequences for human health and disease. The spread of antibiotic resistance genes, virulence, and pathogenicity determinants predominantly occurs by way of HGT. Evidence exists of extensive horizontal transfer in the human gut microbiome. Phage transduction is a type of HGT event in which a bacteriophage transfers non-viral DNA from one bacterial host cell to another. The abundance of tailed bacteriophages in the human gut suggests that transduction could act as a significant mode of HGT in the gut microbiome. Here we review in detail the known mechanisms of phage-mediated HGT, namely specialized and generalized transduction, lateral transduction, gene-transfer agents, and molecular piracy, as well as methods used to detect phage-mediated HGT, and discuss its potential implications for the human gut microbiome.

Leviviricetes: expanding and restructuring the taxonomy of bacteria-infecting single-stranded RNA viruses

The vast majority of described prokaryotic viruses have double-stranded or single-stranded DNA or double-stranded RNA genomes. Until 2020, a mere four prokaryotic single-stranded, positive-sense RNA viruses have been classified in two genera (Riboviria; Lenarviricota; Allassoviricetes; Leviviridae). Several recent metagenomic and metatranscriptomic studies revealed a vastly greater diversity of these viruses in prokaryotic soil communities than ever anticipated. Phylogenetic analysis of these newly discovered viruses prompted the reorganization of class Allassoviricetes, now renamed Leviviricetes, to include two orders, Norzivirales and Timlovirales, and a total of six families, 428 genera and 882 species. Here we outline the new taxonomy of Leviviricetes, approved and ratified in 2021 by the International Committee on Taxonomy of Viruses, and describe open-access hidden Markov models to accommodate the anticipated identification and future classification of hundreds, if not thousands, of additional class members into this new taxonomic framework.

Bacterial Viruses Subcommittee and Archaeal Viruses Subcommittee of the ICTV: update of taxonomy changes in 2021

In this article, we – the Bacterial Viruses Subcommittee and the Archaeal Viruses Subcommittee of the International Committee on Taxonomy of Viruses (ICTV) – summarise the results of our activities for the period March 2020 – March 2021. We report the division of the former Bacterial and Archaeal Viruses Subcommittee in two separate Subcommittees, welcome new members, a new Subcommittee Chair and Vice Chair, and give an overview of the new taxa that were proposed in 2020, approved by the Executive Committee and ratified by vote in 2021. In particular, a new realm, three orders, 15 families, 31 subfamilies, 734 genera and 1845 species were newly created or redefined (moved/promoted).

Long-term persistence of crAss-like phage crAss001 is associated with phase variation in Bacteroides intestinalis

BACKGROUND

The crAss-like phages are ubiquitous and highly abundant members of the human gut virome that infect commensal bacteria of the order Bacteroidales. Although incapable of lysogeny, these viruses demonstrate long-term persistence in the human gut microbiome, dominating the virome in some individuals.

RESULTS

Here we show that rapid phase variation of alternate capsular polysaccharides in Bacteroides intestinalis cultures plays an important role in a dynamic equilibrium between phage sensitivity and resistance, allowing phage and bacteria to multiply in parallel. The data also suggests the role of a concomitant phage persistence mechanism associated with delayed lysis of infected cells, similar to carrier state infection. From an ecological and evolutionary standpoint, this type of phage-host interaction is consistent with the Piggyback-the-Winner model, which suggests a preference towards lysogenic or other "benign" forms of phage infection when the host is stably present at high abundance.

CONCLUSION

Long-term persistence of bacteriophage and host could result from mutually beneficial mechanisms driving bacterial strain-level diversity and phage survival in complex environments.

Stability of the human gut virome and effect of gluten-free diet

The human gut microbiome consists of bacteria, archaea, eukaryotes, and viruses. The gut viruses are relatively underexplored. Here, we longitudinally analyzed the gut virome composition in 11 healthy adults: its stability, variation, and the effect of a gluten-free diet. Using viral enrichment and a de novo assembly-based approach, we demonstrate the quantitative dynamics of the gut virome, including dsDNA, ssDNA, dsRNA, and ssRNA viruses. We observe highly divergent individual viral communities, carrying on an average 2,143 viral genomes, 13.1% of which were present at all 3 time points. In contrast to previous reports, the Siphoviridae family dominates over Microviridae in studied individual viromes. We also show individual viromes to be stable at the family level but to vary substantially at the genera and species levels. Finally, we demonstrate that lower initial diversity of the human gut virome leads to a more pronounced effect of the dietary intervention on its composition.

Isolation and characterisation of ΦcrAss002, a crAss-like phage from the human gut that infects Bacteroides xylanisolvens

BACKGROUND

The gut phageome comprises a complex phage community of thousands of individual strains, with a few highly abundant bacteriophages. CrAss-like phages, which infect bacteria of the order Bacteroidales, are the most abundant bacteriophage family in the human gut and make an important contribution to an individual's core virome. Based on metagenomic data, crAss-like phages form a family, with four sub-families and ten candidate genera. To date, only three representatives isolated in pure culture have been reported: ΦcrAss001 and two closely related phages DAC15 and DAC17; all are members of the less abundant candidate genus VI. The persistence at high levels of both crAss-like phage and their Bacteroidales hosts in the human gut has not been explained mechanistically, and this phage-host relationship can only be properly studied with isolated phage-host pairs from as many genera as possible.

RESULTS

Faeces from a healthy donor with high levels of crAss-like phage was used to initiate a faecal fermentation in a chemostat, with selected antibiotics chosen to inhibit rapidly growing bacteria and selectively enrich for Gram-negative Bacteroidales. This had the objective of promoting the simultaneous expansion of crAss-like phages on their native hosts. The levels of seven different crAss-like phages expanded during the fermentation, indicating that their hosts were also present in the fermenter. The enriched supernatant was then tested against individual Bacteroidales strains isolated from the same faecal sample. This resulted in the isolation of a previously uncharacterised crAss-like phage of candidate genus IV of the proposed Alphacrassvirinae sub-family, ΦcrAss002, that infects the gut commensal Bacteroides xylanisolvens. ΦcrAss002 does not form plaques or spots on lawns of sensitive cells, nor does it lyse liquid cultures, even at high titres. In keeping with the co-abundance of phage and host in the human gut, ΦcrAss002 and Bacteroides xylanisolvens can also co-exist at high levels when co-cultured in laboratory media.

CONCLUSIONS

We report the isolation and characterisation of ΦcrAss002, the first representative of the proposed Alphacrassvirinae sub-family of crAss-like phages. ΦcrAss002 cannot form plaques or spots on bacterial lawns but can co-exist with its host, Bacteroides xylanisolvens, at very high levels in liquid culture without impacting on bacterial numbers. Video abstract.

Probing the "Dark Matter" of the Human Gut Phageome: Culture Assisted Metagenomics Enables Rapid Discovery and Host-Linking for Novel Bacteriophages

Recent years have been marked by the growing interest towards virulent and temperate bacteriophage populations inhabiting the human lower gastrointestinal tract – the gut phageome. A number of studies demonstrated high levels of specificity and temporal stability of individual gut phageomes, as well as their specific alterations in disease cohorts, in parallel with changes in the bacteriome. It has been speculated that phages might have an active role in shaping the taxonomic composition and functional properties of the human gut bacteriome. An overwhelming majority of gut bacteriophages, however, remain uncultured, unclassified, and their specific hosts and infection strategies are still unknown. They are often referred to as “the viral dark matter”. A possible breakthrough in understanding of the phageome can only become possible when a significant proportion of the “the viral dark matter” is identified and linked to bacterial hosts. Here, we describe a method that enables rapid discovery and host-linking of novel bacteriophages in the gut via a combination of serial enrichment cultures and shotgun metagenomics of viral DNA. Using this approach dozens of novel and previously known bacteriophages were detected, including the ones infecting difficult-to-culture anaerobic bacteria. The majority of phages failed to produce lysis and propagate on host cultures in traditional assays. The newly identified phages include representatives of Siphoviridae, Myoviridae, Podoviridae, and crAss-like viruses, infecting diverse bacterial taxa of Bacteroidetes, Firmicutes, Actinobacteria, Verrucomicrobia and Proteobacteria phyla. The proposed new method has a potential for high-throughput screening applications for mass discovery of new phages in different environments.

Diverse Bacteriocins Produced by Strains From the Human Milk Microbiota

Microbial colonization of the infant gut is a convoluted process dependent on numerous contributing factors, including age, mode of delivery and diet among others that has lifelong implication for human health. Breast milk also contains a microbiome which acts as a source of colonizing bacteria for the infant. Here, we demonstrate that human milk harbors a wide diversity of bacteriocin-producing strains with the potential to compete among the developing gut microbiota of the infant. We screened 37 human milk samples and found isolates with antimicrobial activity and distinct cross-immunity profiles. From these isolates, we detected 73 putative gene clusters for bacteriocins of all known sub-classes, including 16 novel prepeptides. More specifically, we detected two novel lantibiotics, four sactibiotics and three class IIa bacteriocins with an unusual modification of the pediocin box that is composed of YDNGI instead of the highly conserved motif YGNGV. Moreover, we identified a novel class IIb bacteriocin, four novel class IIc and two class IId bacteriocins. In conclusion, human milk contains a variety of bacteriocin-producing strains which may provide them a competitive advantage in the colonization of the infant gut and suggests that the milk microbiota is a source of antimicrobial potential.

Bacteriophages of the Human Gut: The "Known Unknown" of the Microbiome

The human gut microbiome is a dense and taxonomically diverse consortium of microorganisms. While the bacterial components of the microbiome have received considerable attention, comparatively little is known about the composition and physiological significance of human gut-associated bacteriophage populations (phageome). By extrapolating our knowledge of phage-host interactions from other environments, one could expect that >10¹² viruses reside in the human gut, and we can predict that they play important roles in regulating the complex microbial networks operating in this habitat. Before delving into their function, we need to first overcome the challenges associated with studying and characterizing the phageome. In this Review, we summarize the available methods and main findings regarding taxonomic composition, community structure, and population dynamics in the human gut phageome. We also discuss the main challenges in the field and identify promising avenues for future research.

Comparative analysis of Faecalibacterium prausnitzii genomes shows a high level of genome plasticity and warrants separation into new species-level taxa

Background

Faecalibacterium prausnitzii is a ubiquitous member of the human gut microbiome, constituting up to 15% of the total bacteria in the human gut. Substantial evidence connects decreased levels of F. prausnitzii with the onset and progression of certain forms of inflammatory bowel disease, which has been attributed to its anti-inflammatory potential. Two phylogroups of F. prausnitzii have been identified, with a decrease in phylogroup I being a more sensitive marker of intestinal inflammation. Much of the genomic and physiological data available to date was collected using phylogroup II strains. Little analysis of F. prausnitzii genomes has been performed so far and genetic differences between phylogroups I and II are poorly understood.

Results

In this study we sequenced 11 additional F. prausnitzii genomes and performed comparative genomics to investigate intraspecies diversity, functional gene complement and the mobilome of 31 high-quality draft and complete genomes. We reveal a very low level of average nucleotide identity among F. prausnitzii genomes and a high level of genome plasticity. Two genomogroups can be separated based on differences in functional gene complement, albeit that this division does not fully agree with separation based on conserved gene phylogeny, highlighting the importance of horizontal gene transfer in shaping F. prausnitzii genomes. The difference between the two genomogroups is mainly in the complement of genes associated with catabolism of carbohydrates (such as a predicted sialidase gene in genomogroup I) and amino acids, as well as defense mechanisms.

Conclusions

Based on the combination of ANI of genomic sequences, phylogenetic analysis of core proteomes and functional differences we propose to separate the species F. prausnitzii into two new species level taxa: F. prausnitzii sensu stricto (neotype strain A2–165^T = DSM 17677^T = JCM 31915^T) and F. moorei sp. nov. (type strain ATCC 27768^T = NCIMB 13872^T).

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5313-6) contains supplementary material, which is available to authorized users.

ΦCrAss001 represents the most abundant bacteriophage family in the human gut and infects Bacteroides intestinalis

CrAssphages are an extensive and ubiquitous family of tailed bacteriophages, predicted to infect bacteria of the order Bacteroidales. Despite being found in ~50% of individuals and representing up to 90% of human gut viromes, members of this viral family have never been isolated in culture and remain understudied. Here, we report the isolation of a CrAssphage (ΦCrAss001) from human faecal material. This bacteriophage infects the human gut symbiont Bacteroides intestinalis, confirming previous in silico predictions of the likely host. DNA sequencing demonstrates that the bacteriophage genome is circular, 102 kb in size, and has unusual structural traits. In addition, electron microscopy confirms that ΦcrAss001 has a podovirus-like morphology. Despite the absence of obvious lysogeny genes, ΦcrAss001 replicates in a way that does not disrupt proliferation of the host bacterium, and is able to maintain itself in continuous host culture during several weeks.

Reproducible protocols for metagenomic analysis of human faecal phageomes

BACKGROUND

Recent studies have demonstrated that the human gut is populated by complex, highly individual and stable communities of viruses, the majority of which are bacteriophages. While disease-specific alterations in the gut phageome have been observed in IBD, AIDS and acute malnutrition, the human gut phageome remains poorly characterised. One important obstacle in metagenomic studies of the human gut phageome is a high level of discrepancy between results obtained by different research groups. This is often due to the use of different protocols for enriching virus-like particles, nucleic acid purification and sequencing. The goal of the present study is to develop a relatively simple, reproducible and cost-efficient protocol for the extraction of viral nucleic acids from human faecal samples, suitable for high-throughput studies. We also analyse the effect of certain potential confounding factors, such as storage conditions, repeated freeze-thaw cycles, and operator bias on the resultant phageome profile. Additionally, spiking of faecal samples with an exogenous phage standard was employed to quantitatively analyse phageomes following metagenomic sequencing. Comparative analysis of phageome profiles to bacteriome profiles was also performed following 16S rRNA amplicon sequencing.

RESULTS

Faecal phageome profiles exhibit an overall greater individual specificity when compared to bacteriome profiles. The phageome and bacteriome both exhibited moderate change when stored at + 4 °C or room temperature. Phageome profiles were less impacted by multiple freeze-thaw cycles than bacteriome profiles, but there was a greater chance for operator effect in phageome processing. The successful spiking of faecal samples with exogenous bacteriophage demonstrated large variations in the total viral load between individual samples.

CONCLUSIONS

The faecal phageome sequencing protocol developed in this study provides a valuable additional view of the human gut microbiota that is complementary to 16S amplicon sequencing and/or metagenomic sequencing of total faecal DNA. The protocol was optimised for several confounding factors that are encountered while processing faecal samples, to reduce discrepancies observed within and between research groups studying the human gut phageome. Rapid storage, limited freeze-thaw cycling and spiking of faecal samples with an exogenous phage standard are recommended for optimum results.

[Comparative Genotyping of Staphylococcus aureus Strains Isolated from Skin Lesions, Nasal Cavities, and Feces of Children with Atopic Dermatitis]

Background

The lesion of skin of the majority atopic dermatitis patients is chronically colonized by bacteria belonging to the species Staphylococcus aureus. Topical antibacterial and anti-inflammatory therapy treatment are often ineffective due to fast recolonization by S. aureus and exacerbation of allergic process.

Aims

Our aim was to determine a frequency of S. aureus colonization in skin lesions, mucous membranes of the nasal cavity and intestine of children with atopic dermatitis, to compare the genotypes of Staphylococcus aureus strains isolated from different biotopes of atopic dermatitis patients, and to clarify whether the intestinal and nasal cavities microbiota may act as a source of S. aureus recolonization of skin lesions.

Materials and Methods

Bacteriological examination of fecal samples, skin, and nasal swabs was conducted in 38 atopic dermatitis patients. The pure bacterial cultures of S. aureus were identified using API Staph (Biomerieux, France) and Vitek 2 MS (Biomerieux, France). Isolates of S. aureus were subjected to genotyping by analysis of rRNA internal 16S-23S rRNA spacer regions and high resolution melting analysis (HMR) of polymorphic spa X-regions.

Results

99% S. aureus strains were successfully identified using MALDI-TOF mass-spectrometry. S. aureus cultures were isolated from all biotopes in 31,6% of children, from skin and nasal cavities — in 42% of cases, from skin and feces — in 2,6% of cases, only from skin — in 10,5%, from nasal cavities and feces — in 2,6%, and only from nasal cavities — in 2,6% of cases. In 8% of children, S. aureus was not detected in any of the biotopes. Genotyping of the isolates enabled the detection of 17 different genotypes. A match between the genotypes of skin and nasal strains, and skin and fecal strains was observed in 88% and 61% of the cases respectively.

Conclusions

The observed a high-frequency matching genotypes suggests the possibility of migration of S. aureus strains inside biotopes in humans and the absence of specialization to colonization of any of the niches.

Production of biologically active scFv and VHH antibody fragments in Bifidobacterium longum

Bifidobacteria constitute a significant part of healthy intestinal microbiota in adults and infants and present a promising platform for construction of genetically modified probiotic agents for treatment of gastrointestinal disorders. In this study, three strains of Bifidobacterium longum were constructed that express and secrete biologically active single-chain antibodies against human TNF-α and Clostridium difficile exotoxin A. Anti-TNF-α scFv antibody D2E7 was produced at the level of 25 μg L(-1) in broth culture and was mostly retained in the cytoplasm, while VHH-type antibodies A20.1 and A26.8 against C. difficile exotoxin A were produced at the levels of 0.3-1 mg L(-1) and secreted very efficiently. The biological activity of both antibody types was demonstrated in the mammalian cell-based assays. Expression of A20.1 and A26.8 was also observed in vivo after intragastric administration of transformed B. longum strains to (C57/BL6 × DBA/2)F1 mice. The obtained B. longum strains may serve as prototypes for construction of novel probiotic medications against inflammatory bowel disease and C. difficile-associated disease.

[Species Diversity of Bifidobacteria in the Intestinal Microbiota Studied Using MALDI-TOF Mass-Spectrometry]

BACKGROUND

The members of genus Bifidobacterium represent a significant part of intestinal microbiota in adults and predominate in infants. Species repertoire of the intestinal bifidobacteria is known to be subjected to major changes with age; however, many details of this process are still to be elucidated.

OBJECTIVE

Our aim was to study the diversity of intestinal bifidobacteria and changes of their qualitative and quantitative composition characteristics during the process of growing up using MALDI-TOF mass-spectrometric analysis ofpure bacterial cultures.

METHODS

A cross-sectional study of bifidobacteria in the intestinal microbiota was performed in 93 healthy people of the ages from 1 month to 57 years. Strains were identified using Microflex LT MALDI-TOF MS, the confirmation was performed by 16S rRNA gene fragment sequencing.

RESULTS

93% of isolated bifidobacterial strains were successfully identified using MALDI-TOF mass-spectrometry. At least two of the strains from each species were additionally identified by 16S rRNA gene fragment sequencing, in all of the cases the results were the same. It was shown that the total concentration of bifidobacteria decreases with age (p<0.001) as well as the frequency of isolation of Bifidobacterium bifidum (p=0.020) and Bifidobacterium breve (p<0.001), and the frequency of isolation of Bifidobacterium adolescentis, increases (p<0.001), representing the continuous process of transformation of microbiota.

CONCLUSION

The method of MALDI-TOF mass spectrometry demonstrated the ability to perform rapid and reliable identification of bifidobacteria that allowed the study of changes in the quantitative and qualitative characteristics of human microbiota in the process of growing up.

Characteristics of new monomolecular chimeric T-cell receptors to carcinoembryonic antigen

We described two original genetic constructs encoding chimeric monomolecular T-cell receptors, where the effector T-cell receptor fragment was linked with the antigen-recognizing part consisting of two variable fragments of two different antibodies to carcinoembryonic antigen. Following transfection, these receptors were expressed on the cell surface and bound carcinoembryonic antigen. Human peripheral blood lymphocytes transfected with the above constructs demonstrated high cytotoxic activity against HCT116 cells expressing carcinoembryonic antigen.

Heterologous expression of secreted biologically active human interleukin-10 in Bifidobacterium breve

Construction of Bifidobacterium breve capable of production of secreted biologically active human interleukin-10 (hIL-10) is described. ORF coding for full-length mature human interleukin-10 was cloned into a series of expression vectors. This resulted in generation of translational fusions between hIL-10 and signal peptides sequences derived from Bifidobacterium breve genes sec2, apuB and B. adolescentis gene amyB under the control of constitutively active bifidobacterial promoter. We have shown that fusion to amyB signal peptide resulted in highest expression level of hIL-10 at the mRNA and protein level. Secreted hIL-10 was highly unstable in bifidobacterial culture supernatants in standard growth conditions. However, incubation of stationary cultures in buffered tissue culture medium resulted in production of stable biologically active hIL-10, albeit in low amounts (1.9 ng/ml).

Relationship between suppression of E6 and E7 virus oncogenes and expression of apoptosis and cell cycle genes in cervical cancer culture

The effects of short interfering RNA suppressing the expression of E6 and E7 human papilloma virus (type 18) on the expression of apoptosis and cell cycle genes were studied in HeLa cells. Changes in the transcription profiles were evaluated using DNA microarray and real-time reverse-transcription PCR. Cell transfection with anti-E6 and anti-E7 short interfering RNA moderately reduced the expression of mRNA for CDC25C, GRB2, GTSE1, and PLK1 genes and induced expression of CDKN1A (p21(CIP)) gene mRNA. In addition, culture proliferation was inhibited and morphological changes characteristic of differentiation and cell aging developed.

[Expression of green fluorescent protein (GFP) gene of Aequorea victoria [correction of Aequoria victoria] in Lactobacillus plantarum bacterium ]

Results of development of shuttle expressing plasmid vector Escherichia coli-Lactobacillus which allowed high level expression of heterologous genes in lactobacilli are represented. Vector pTRKH2 which is able to replicate in E. coli and in wide range of Gram-positive bacteria was used as the base. In order to provide high level of cloned gene expression constitutive-active synthetic promoter, site of initiation of translation, and terminator of transcription were introduced in the vector. Functional activity of this vector was confirmed using green fluorescent protein (GFP) gene from Aequoria victoria. Transformation of model strain by gfp gene-carrying plasmid resulted in appearance of typical fluorescent phenotype.

Production of human basic fibroblast growth factor (FGF-2) in Bifidobacterium breve using a series of novel expression/secretion vectors

Four E. coli-Bifidobacterium shuttle vectors were constructed using Bifidobacterium plasmids, pB44 and pB80. The vectors carry two bifidobacterial promoters, a signal peptide-encoding sequence, sec2, of Bifidobacterium breve, and a transcriptional terminator from hup gene of Bifidobacterium longum. Functionality of the constructs were tested using human FGF-2 gene. The expression of FGF-2 was detected by Western blotting in B. breve transformed with three of the vectors. The highest amount of FGF-2 was produced upon transformation with pESH86, which is a pB80-based plasmid carrying FGF-2 under control of a hup promoter (Phup). Similarly, the level of FGF-2 mRNA transcribed from pESH86 was approximately threefold higher, 882 +/- 70 AU (arbitrary units), when compared to those transcribed from pB44-based pESH46 (Phup) (289 +/- 65 AU) and pESH47 (Pgap) (282 +/- 37 AU). These results suggest the vectors have the potential for production of exported fusion proteins in bifidobacteria and the expression levels can be regulated through the employment of different bifidobacterial promoters and/or replicons.

[Bifidobacterial plasmids and their application to genetic engineering]

Representatives of Bifidobacterium genus are considered to play many important roles in intestinal homeostasis. On the other hand, their molecular biology and genetics have been poorly studied. In order to broaden our understanding of their health-promoting mechanisms, it is extremely important to possess tools to manipulate them genetically. Another challenging task is to take advantage of genetic engineering technology for designing new probiotic bifidobacteria with unique therapeutic properties. An important step in such work is to isolate and characterize small bifidobacterial plasmids, which can be applied to the construction of cloning vectors. This article presents a review of several pioneering studied devoted to bifidobacterial plasmids and genetic engineering with bifidobacteria. Trends in and prospects of molecular genetics of bifidobacteria are discussed as well.

Structural basis for the fast maturation of Arthropoda green fluorescent protein

Since the cloning of Aequorea victoria green fluorescent protein (GFP) in 1992, a family of known GFP-like proteins has been growing rapidly. Today, it includes more than a hundred proteins with different spectral characteristics cloned from Cnidaria species. For some of these proteins, crystal structures have been solved, showing diversity in chromophore modifications and conformational states. However, we are still far from a complete understanding of the origin, functions and evolution of the GFP family. Novel proteins of the family were recently cloned from evolutionarily distant marine Copepoda species, phylum Arthropoda, demonstrating an extremely rapid generation of fluorescent signal. Here, we have generated a non-aggregating mutant of Copepoda fluorescent protein and solved its high-resolution crystal structure. It was found that the protein beta-barrel contains a pore, leading to the chromophore. Using site-directed mutagenesis, we showed that this feature is critical for the fast maturation of the chromophore.

[A molecular-and-genetic analysis of species and strain diversity of bifidobacteria in early childhood]

The species and strain composition of bifidobacteria in 29 children both sexes, aged 8 to 16 months, was studied. Species-specific primers and PCR were used to determine to which species the predominant strains of bifidobacteria, isolated from feces by cultural methods, belonged. Bifidobacteria were found in 28 (96.5%) children; their number was 10.2 +/- 0.7 ECU per a gram of the material. B. longum and B. bifidum were frequent (71.4 and 53.5%, respectively). The level of quantitative detection used in the study also allowed revealing of B. catenulatum (17.9%) and B. breve (14.4%). A high titer of B. dentium was found in one case (3.6%). B. adolescentis and B. angulatum were not found in any patient. The average number of species found in one child was 1.7 +/- 0.7. RAPD-PCR and investigation of plasmid profile were used to determine possible belonging of the isolates to different strains. The average number of strains per one sample was 2.3 +/- 1.2. Nine unique plasmid bifidobacterial strains were isolated from 7 children. In 3 children the intestinal tract was found to be colonized by both plasmid and non-plasmid-carrying strains of one bifidobacterial species.

[Peculiarities of microbial colonization of the intestinal tract in newborns and pre-term infants in intensive care units]

The aim of the study was to compare the development of intestinal microflora in clinically healthy newborns, born by mothers with physiological pregnancy, and in small premature infants, who were treated in intensive care units (ICU) using various regimens of antibacterial therapy. The study revealed that the most frequent bacteria found in the intestinal tract of healthy infants at the and of neonatal period were bifidobacteria, enterobacteria, and coagulase-negative staphylococci and enterococci. Together with large quantity of autochtonous bacteria, the study revealed conditionally pathogenic microorganisms, such as klebsiella and coagulase-positive staphylococci at the end of neonatal period. The intestinal microflora of premature infants in ICU, treated with a combination of third generation cephalosporins and aminoglycosides from the first hours of life, was characterized by total absence of indigenous microflora, and prevalence of enterococci and staphylococci. The results show that the first stage of antibacterial therapy of preterm infants in ICU should be based upon the principles of selective decontamination.