The Significance of Mutualistic Phages for Bacterial Ecology and Evolution

A game of resistance: War between bacteria and phages and how phage cocktails can be the solution

While phages hold promise as an antibiotic alternative, they encounter significant challenges in combating bacterial infections, primarily due to the emergence of phage-resistant bacteria. Bacterial defence mechanisms like superinfection exclusion, CRISPR, and restriction-modification systems can hinder phage effectiveness. Innovative strategies, such as combining different phages into cocktails, have been explored to address these challenges. This review delves into these defence mechanisms and their impact at each stage of the infection cycle, their challenges, and the strategies phages have developed to counteract them. Additionally, we examine the role of phage cocktails in the evolving landscape of antibacterial treatments and discuss recent studies that highlight the effectiveness of diverse phage cocktails in targeting essential bacterial receptors and combating resistant strains.

Soil keystone viruses are regulators of ecosystem multifunctionality

Ecosystem multifunctionality reflects the capacity of ecosystems to simultaneously maintain multiple functions which are essential bases for human sustainable development. Whereas viruses are a major component of the soil microbiome that drive ecosystem functions across biomes, the relationships between soil viral diversity and ecosystem multifunctionality remain under-studied. To address this critical knowledge gap, we employed a combination of amplicon and metagenomic sequencing to assess prokaryotic, fungal and viral diversity, and to link viruses to putative hosts. We described the features of viruses and their potential hosts in 154 soil samples from 29 farmlands and 25 forests distributed across China. Although 4,460 and 5,207 viral populations (vOTUs) were found in the farmlands and forests respectively, the diversity of specific vOTUs rather than overall soil viral diversity was positively correlated with ecosystem multifunctionality in both ecosystem types. Furthermore, the diversity of these keystone vOTUs, despite being 10-100 times lower than prokaryotic or fungal diversity, was a better predictor of ecosystem multifunctionality and more strongly associated with the relative abundances of prokaryotic genes related to soil nutrient cycling. Gemmatimonadota and Actinobacteria dominated the host community of soil keystone viruses in the farmlands and forests respectively, but were either absent or showed a significantly lower relative abundance in that of soil non-keystone viruses. These findings provide novel insights into the regulators of ecosystem multifunctionality and have important implications for the management of ecosystem functioning.

Fecal virome transplantation: A promising strategy for the treatment of metabolic diseases

Metabolic diseases are a group of disorders caused by metabolic abnormalities, including obesity, diabetes, non-alcoholic fatty liver disease, and more. Increasing research indicates that, beyond inherent metabolic irregularities, the onset and progression of metabolic diseases are closely linked to alterations in the gut microbiota, particularly gut bacteria. Additionally, fecal microbiota transplantation (FMT) has demonstrated effectiveness in clinically treating metabolic diseases, notably diabetes. Recent attention has also focused on the role of gut viruses in disease onset. This review first introduces the characteristics and influencing factors of gut viruses, then summarizes their potential mechanisms in disease development, highlighting their impact on gut bacteria and regulation of host immunity. We also compare FMT, fecal filtrate transplantation (FFT), washed microbiota transplantation (WMT), and fecal virome transplantation (FVT). Finally, we review the current understanding of gut viruses in metabolic diseases and the application of FVT in treating these conditions. In conclusion, FVT may provide a novel and promising treatment approach for metabolic diseases, warranting further validation through basic and clinical research.

Genomic and induction evidence for bacteriophage contributions to sargassum-bacteria symbioses

BACKGROUND

Symbioses between primary producers and bacteria are crucial for nutrient exchange that fosters host growth and niche adaptation. Yet, how viruses that infect bacteria (phages) influence these bacteria-eukaryote interactions is still largely unknown. Here, we investigate the role of viruses on the genomic diversity and functional adaptations of bacteria associated with pelagic sargassum. This brown alga has dramatically increased its distribution range in the Atlantic in the past decade and is predicted to continue expanding, imposing severe impacts on coastal ecosystems, economies, and human health.

RESULTS

We reconstructed 73 bacterial and 3963 viral metagenome-assembled genomes (bMAGs and vMAGs, respectively) from coastal Sargassum natans VIII and surrounding seawater. S. natans VIII bMAGs were enriched in prophages compared to seawater (28% and 0.02%, respectively). Rhodobacterales and Synechococcus bMAGs, abundant members of the S. natans VIII microbiome, were shared between the algae and seawater but were associated with distinct phages in each environment. Genes related to biofilm formation and quorum sensing were enriched in S. natans VIII phages, indicating their potential to influence algal association in their bacterial hosts. In-vitro assays with a bacterial community harvested from sargassum surface biofilms and depleted of free viruses demonstrated that these bacteria are protected from lytic infection by seawater viruses but contain intact and inducible prophages. These bacteria form thicker biofilms when growing on sargassum-supplemented seawater compared to seawater controls, and phage induction using mitomycin C was associated with a significant decrease in biofilm formation. The induced metagenomes were enriched in genomic sequences classified as temperate viruses compared to uninduced controls.

CONCLUSIONS

Our data shows that prophages contribute to the flexible genomes of S. natans VIII-associated bacteria. These prophages encode genes with symbiotic functions, and their induction decreases biofilm formation, an essential capacity for flexible symbioses between bacteria and the alga. These results indicate that prophage acquisition and induction contribute to genomic and functional diversification during sargassum-bacteria symbioses, with potential implications for algae growth. Video Abstract.

Phage predation accelerates the spread of plasmid-encoded antibiotic resistance

Phage predation is generally assumed to reduce microbial proliferation while not contributing to the spread of antibiotic resistance. However, this assumption does not consider the effect of phage predation on the spatial organization of different microbial populations. Here, we show that phage predation can increase the spread of plasmid-encoded antibiotic resistance during surface-associated microbial growth by reshaping spatial organization. Using two strains of the bacterium Escherichia coli, we demonstrate that phage predation slows the spatial segregation of the strains during growth. This increases the number of cell-cell contacts and the extent of conjugation-mediated plasmid transfer between them. The underlying mechanism is that phage predation shifts the location of fastest growth from the biomass periphery to the interior where cells are densely packed and aligned closer to parallel with each other. This creates straighter interfaces between the strains that are less likely to merge together during growth, consequently slowing the spatial segregation of the strains and enhancing plasmid transfer between them. Our results have implications for the design and application of phage therapy and reveal a mechanism for how microbial functions that are deleterious to human and environmental health can proliferate in the absence of positive selection.

Genomic characterization and probiotic potential assessment of an exopolysaccharide-producing strain Pediococcus pentosaceus LL-07 isolated from fermented meat

BACKGROUND

The genomic information available for Pediococcus pentosaceus is primarily derived from fermented fruits and vegetables, with less information available from fermented meat. P. pentosaceus LL-07, a strain isolated from fermented meat, has the capability of producing exopolysaccharides (EPS). To assess the probiotic attributes of P. pentosaceus LL-07, we conducted whole-genome sequencing (WGS) using the PacBio SequelIIe and Illumina MiSeq platforms, followed by in vitro experiments to explore its probiotic potential.

RESULTS

The genome size of P. pentosaceus LL-07 is 1,782,685 bp, comprising a circular chromosome and a circular plasmid. Our investigation revealed the absence of a CRISPR/Cas system. Sugar fermentation experiments demonstrated the characteristics of carbohydrate metabolism. P. pentosaceus LL-07 contains an EPS synthesis gene cluster consisting of 13 genes, which is different from the currently known gene cluster structure. NO genes associated with hemolysis or toxin synthesis were detected. Additionally, eighty-six genes related to antibiotic resistance were identified but not present in the prophage, transposon or plasmid. In vitro experiments demonstrated that P. pentosaceus LL-07 was comparable to the reference strain P. pentosaceus ATCC25745 in terms of tolerance to artificial digestive juice and bile, autoaggregation and antioxidation, and provided corresponding genomic evidence.

CONCLUSION

This study confirmed the safety and probiotic properties of P. pentosaceus LL-07 via complete genome and phenotype analysis, supporting its characterization as a potential probiotic candidate.

Bacterial resistance to temperate phage is influenced by the frequency of lysogenic establishment

Temperate phages can shape bacterial community dynamics and evolution through lytic and lysogenic life cycles. In response, bacteria that resist phage infection can emerge. This study explores phage-based factors that influence bacterial resistance using a model system of temperate P22 phage and Salmonella both inside and outside the mammalian host. Phages that remained functional despite gene deletions had minimal impact on lysogeny and phage resistance except for deletions in the immI region that substantially reduced lysogeny and increased phage resistance to levels comparable to that observed with an obligately lytic P22. This immI deletion does not make the lysogen less competitive but instead increases the frequency of bacterial lysis. Thus, subtle changes in the balance between lysis and lysogeny during the initial stages of infection can significantly influence the extent of phage resistance in the bacterial population. Our work highlights the complex nature of the phage-bacteria-mammalian host triad.

Lytic/Lysogenic Transition as a Life-History Switch

The transition between lytic and lysogenic life cycles is the most important feature of the life-history of temperate viruses. To explain this transition, an optimal life-history model is offered based a discrete-time formulation of phage/bacteria population dynamics that features infection of bacteria by Poisson sampling of virions from the environment. The time step is the viral latency period. In this model, density-dependent viral absorption onto the bacterial surface produces virus/bacteria coexistence and density dependence in bacterial growth is not needed. The formula for the transition between lytic and lysogenic phases is termed the 'fitness switch'. According to the model, the virus switches from lytic to lysogenic when its population grows faster as prophage than as virions produced by lysis of the infected cells, and conversely for the switch from lysogenic to lytic. A prophage that benefits the bacterium it infects automatically incurs lower fitness upon exiting the bacterial genome, resulting in its becoming locked into the bacterial genome in what is termed here as a 'prophage lock'. The fitness switch qualitatively predicts the ecogeographic rule that environmental enrichment leads to microbialization with a concomitant increase in lysogeny, fluctuating environmental conditions promote virus-mediated horizontal gene transfer, and prophage-containing bacteria can integrate into the microbiome of a eukaryotic host forming a functionally integrated tripartite holobiont. These predictions accord more with the 'Piggyback-the-Winner' hypothesis than with the 'Kill-the-Winner' hypothesis in virus ecology.

Diversities and interactions of phages and bacteria in deep-sea sediments as revealed by metagenomics

Phages are found virtually everywhere, even in extreme environments, and are extremely diverse both in their virion structures and in their genomic content. They are thought to shape the taxonomic and functional composition of microbial communities as well as their stability. A number of studies on laboratory culture and viral metagenomic research provide deeper insights into the abundance, diversity, distribution, and interaction with hosts of phages across a wide range of ecosystems. Although most of these studies focus on easily accessible samples, such as soils, lakes, and shallow oceans, little is known about bathypelagic phages. In this study, through analyzing the 16S rRNA sequencing and viral metagenomic sequencing data of 25 samples collected from five different bathypelagic ecosystems, we detected a high diversity of bacteria and phages, particularly in the cold seep and hydrothermal vent ecosystems, which have stable chemical energy. The relative abundance of phages in these ecosystems was higher than in other three abyssal ecosystems. The low phage/host ratios obtained from host prediction were different from shallow ecosystems and indicated the prevalence of prophages, suggesting the complexity of phage-bacteria interactions in abyssal ecosystems. In the correlation analysis, we revealed several phages-bacteria interaction networks of potential ecological relevance. Our study contributes to a better understanding of the interactions between bathypelagic bacteria and their phages.

Macroalgal virosphere assists with host-microbiome equilibrium regulation and affects prokaryotes in surrounding marine environments

The microbiomes in macroalgal holobionts play vital roles in regulating macroalgal growth and ocean carbon cycling. However, the virospheres in macroalgal holobionts remain largely underexplored, representing a critical knowledge gap. Here we unveil that the holobiont of kelp (Saccharina japonica) harbors highly specific and unique epiphytic/endophytic viral species, with novelty (99.7% unknown) surpassing even extreme marine habitats (e.g. deep-sea and hadal zones), indicating that macroalgal virospheres, despite being closest to us, are among the least understood. These viruses potentially maintain microbiome equilibrium critical for kelp health via lytic-lysogenic infections and the expression of folate biosynthesis genes. In-situ kelp mesocosm cultivation and metagenomic mining revealed that kelp holobiont profoundly reshaped surrounding seawater and sediment virus-prokaryote pairings through changing surrounding environmental conditions and virus-host migrations. Some kelp epiphytic viruses could even infect sediment autochthonous bacteria after deposition. Moreover, the presence of ample viral auxiliary metabolic genes for kelp polysaccharide (e.g. laminarin) degradation underscores the underappreciated viral metabolic influence on macroalgal carbon cycling. This study provides key insights into understanding the previously overlooked ecological significance of viruses within macroalgal holobionts and the macroalgae-prokaryotes-virus tripartite relationship.

Role of bacteriophages in shaping gut microbial community

Phages are the most diversified and dominant members of the gut virobiota. They play a crucial role in shaping the structure and function of the gut microbial community and consequently the health of humans and animals. Phages are found mainly in the mucus, from where they can translocate to the intestinal organs and act as a modulator of gut microbiota. Understanding the vital role of phages in regulating the composition of intestinal microbiota and influencing human and animal health is an emerging area of research. The relevance of phages in the gut ecosystem is supported by substantial evidence, but the importance of phages in shaping the gut microbiota remains unclear. Although information regarding general phage ecology and development has accumulated, detailed knowledge on phage-gut microbe and phage-human interactions is lacking, and the information on the effects of phage therapy in humans remains ambiguous. In this review, we systematically assess the existing data on the structure and ecology of phages in the human and animal gut environments, their development, possible interaction, and subsequent impact on the gut ecosystem dynamics. We discuss the potential mechanisms of prophage activation and the subsequent modulation of gut bacteria. We also review the link between phages and the immune system to collect evidence on the effect of phages on shaping the gut microbial composition. Our review will improve understanding on the influence of phages in regulating the gut microbiota and the immune system and facilitate the development of phage-based therapies for maintaining a healthy and balanced gut microbiota.

A Novel Podophage StenR_269 Suggests a New Family in the Class Caudoviricetes

Stenotrophomonas rhizophila was first discovered in soil; it is associated with the rhizosphere and capable of both protecting roots and stimulating plant growth. Therefore, it has a great potential to be used in biocontrol. The study of S. rhizophila phages is important for a further evaluation of their effect on the fitness and properties of host bacteria. A novel phage StenR_269 and its bacterial host S. rhizophila were isolated from a soil sample in the remediation area of a coal mine. Electron microscopy revealed a large capsid (~Ø80 nm) connected with a short tail, which corresponds to the podovirus morphotype. The length of the genomic sequence of the StenR_269 was 66,322 bp and it contained 103 putative genes; 40 of them encoded proteins with predicted functions, 3 corresponded to tRNAs, and the remaining 60 were identified as hypothetical ones. Comparative analysis indicated that the StenR_269 phage had a similar genome organization to that of the unclassified Xanthomonas phage DES1, despite their low protein similarity. In addition, the signature proteins of StenR_269 and DES1 had low similarity and these proteins clustered far from the corresponding proteins of classified phages. Thus, the StenR_269 genome is orphan and the analyzed data suggest a new family in the class Caudoviricetes.

The social lives of viruses and other mobile genetic elements: a commentary on Leeks et al. 2023

Illustration of life-histories of phages and plasmids through horizontal and vertical transmission (see Figure 1 for more information).

Phage Interactions with the Nervous System in Health and Disease

The central nervous system manages all of our activities (e.g., direct thinking and decision-making processes). It receives information from the environment and responds to environmental stimuli. Bacterial viruses (bacteriophages, phages) are the most numerous structures occurring in the biosphere and are also found in the human organism. Therefore, understanding how phages may influence this system is of great importance and is the purpose of this review. We have focused on the effect of natural bacteriophages in the central nervous system, linking them to those present in the gut microbiota, creating the gut-brain axis network, as well as their interdependence. Importantly, based on the current knowledge in the field of phage application (e.g., intranasal) in the treatment of bacterial diseases associated with the brain and nervous system, bacteriophages may have significant therapeutic potential. Moreover, it was indicated that bacteriophages may influence cognitive processing. In addition, phages (via phage display technology) appear promising as a targeted therapeutic tool in the treatment of, among other things, brain cancers. The information collected and reviewed in this work indicates that phages and their impact on the nervous system is a fascinating and, so far, underexplored field. Therefore, the aim of this review is not only to summarize currently available information on the association of phages with the nervous system, but also to stimulate future studies that could pave the way for novel therapeutic approaches potentially useful in treating bacterial and non-bacterial neural diseases.

Soil viral diversity, ecology and climate change

Soil viruses are highly abundant and have important roles in the regulation of host dynamics and soil ecology. Climate change is resulting in unprecedented changes to soil ecosystems and the life forms that reside there, including viruses. In this Review, we explore our current understanding of soil viral diversity and ecology, and we discuss how climate change (such as extended and extreme drought events or more flooding and altered precipitation patterns) is influencing soil viruses. Finally, we provide our perspective on future research needs to better understand how climate change will impact soil viral ecology.

Complete genome sequence analysis, morphology and structural protein identification of two Bacillus subtilis phages, BSTP4 and BSTP6, which may form a new species in the genus Salasvirus

In the present study, two new Bacillus subtilis phages, BSTP4 and BSTP6, were isolated and studied further. Morphologically, BSTP4 and BSTP6 are podoviruses with complete genome of 19,145 (39.9% G + C content) and 19,367 bp (39.8% G + C content), respectively, which became among the smallest Bacillus phages. Three most prominent structural proteins were separated and identified as pre-neck appendage, major head, and head fiber proteins using LC-MS/MS. Both phages encode putative terminal proteins (TP) and contain short inverted terminal repeats (ITRs) which may be important for their replication. In addition, non-coding RNA (pRNA) and parS sites were identified which may be required for DNA packaging and their maintenance inside the host, respectively. Furthermore, the phage genome sequences show significant similarity to B. subtilis group species genome sequences. Finally, phylogenomic and phylogenetic analyses suggest that BSTP4 and BSTP6 may form a new species in the genus Salasvirus, subfamily Picovirinae of family Salasmaviridae. Considering the small numbers of ICTV-accepted B. subtilis phages and the importance of the host in the food industry and biotechnology, the current study helps to improve our understanding of the diversity of B. subtilis phages and shed light on the phage-host relationships.

Potato root-associated microbiomes adapt to combined water and nutrient limitation and have a plant genotype-specific role for plant stress mitigation

BACKGROUND

Due to climate change and reduced use of fertilizers combined stress scenarios are becoming increasingly frequent in crop production. In a field experiment we tested the effect of combined water and phosphorus limitation on the growth performance and plant traits of eight tetraploid and two diploid potato varieties as well as on root-associated microbiome diversity and functional potential. Microbiome and metagenome analysis targeted the diversity and potential functions of prokaryotes, fungi, plasmids, and bacteriophages and was linked to plant traits like tuber yield or timing of canopy closure.

RESULTS

The different potato genotypes responded differently to the combined stress and hosted distinct microbiota in the rhizosphere and the root endosphere. Proximity to the root, stress and potato genotype had significant effects on bacteria, whereas fungi were only mildly affected. To address the involvement of microbial functions, we investigated well and poorly performing potato genotypes (Stirling and Desirée, respectively) under stress conditions and executed a metagenome analysis of rhizosphere microbiomes subjected to stress and no stress conditions. Functions like ROS detoxification, aromatic amino acid and terpene metabolism were enriched and in synchrony with the metabolism of stressed plants. In Desirée, Pseudonocardiales had the genetic potential to take up assimilates produced in the fast-growing canopy and to reduce plant stress-sensing by degrading ethylene, but overall yield losses were high. In Stirling, Xanthomonadales had the genetic potential to reduce oxidative stress and to produce biofilms, potentially around roots. Biofilm formation could be involved in drought resilience and nutrient accessibility of Stirling and explain the recorded low yield losses. In the rhizosphere exposed to combined stress, the relative abundance of plasmids was reduced, and the diversity of phages was enriched. Moreover, mobile elements like plasmids and phages were affected by combined stresses in a genotype-specific manner.

CONCLUSION

Our study gives new insights into the interconnectedness of root-associated microbiota and plant stress responses in the field. Functional genes in the metagenome, phylogenetic composition and mobile elements play a role in potato stress adaption. In a poor and a well performing potato genotype grown under stress conditions, distinct functional genes pinpoint to a distinct stress sensing, water availability and compounds in the rhizospheres.

Bacteriophage-based biocontrol technology to enhance the efficiency of wastewater treatment and reduce targeted bacterial biofilms

Wastewater treatment is an essential process for public health and a sustainable ecosystem. Inadequate wastewater treatment can lead to the release of organic and inorganic pollutants and pathogenic bacteria into the receiving waters which could be further utilized for recreation purposes. The interaction between bacteriophage and bacteria in a wastewater treatment plant plays a major role in maintaining the treatment process. Phage therapy has been proposed as an alternative to conventional treatment methods as bacteriophages can be used on specific targets and leave useful bacteria unharmed. The bacterial species, which are responsible for bulking, foaming, and biofilm formation in a wastewater treatment plant (WWTP) have been identified and their respective phages are isolated to control their growth. Phages with lytic life cycles are preferred to lysogenic. Lytic phages can kill the specific target as they lyse the cell, infect most of the hosts, and have an immediate effect on controlling problems caused by bacteria in a WWTP. The bacteriophages such as T7, SPI1, GTE7, PhaxI, MAG1, MAG2, ϕPh_Se01, ϕPh_Se02, and Bxb1 have been investigated for the removal of bacterial biofilms from wastewater. Novel experimental setups have improved the efficiency of phage therapy in small-scale and pilot-scale experiments. Much more in-depth knowledge of the microbial community and their interaction would help promote the usage of phage therapy in large-scale wastewater treatments. This paper has covered the recent advancements in phage therapy as an effective biocontrol of pathogenic bacteria in the wastewater treatment process and has looked at certain shortcomings that have to be improved.

Viruses Regulate Microbial Community Assembly Together with Environmental Factors in Acid Mine Drainage

Viruses are widespread in various ecosystems, and they play important roles in regulating the microbial community via host-virus interactions. Recently, metagenomic studies showed that there are extremely diverse viruses in different environments from the ocean to the human gut, but the influences of viral communities on microbial communities are poorly understood, especially in extreme environments. Here, we used metagenomics to characterize microbial communities and viral communities in acid mine drainage (AMD) and evaluated how viruses shape microbial community constrained by the harsh environments. Our results showed that AMD viral communities are significantly associated with the microbial communities, and viral diversity has positive correlations with microbial diversity. Viral community explained more variations of microbial community composition than environmental factors in AMD of a polymetallic mine. Moreover, we found that viruses harboring adaptive genes regulate a relative abundance of hosts under the modulation of environmental factors, such as pH. We also observed that viral diversity has significant correlations with the global properties of microbial cooccurrence networks, such as modularity. In addition, the results of null modeling analyses revealed that viruses significantly affect microbial community phylogeny and play important roles in regulating ecological processes of community assembly, such as dispersal limitation and homogenous dispersal. Together, these results revealed that AMD viruses are critical forces driving microbial network and community assembly via host-virus interactions. IMPORTANCE Viruses as mobile genetic elements play critical roles in the adaptive evolution of their hosts in extreme environments. However, how viruses further influence microbial community structure and assembly is still unclear. A recent metagenomic study observed diverse viruses unexplored in acid mine drainage, revealing the associations between the viral community and environmental factors. Here, we showed that viruses together with environmental factors can constrain the relative abundance of host and microbial community assembly in AMD of copper mines and polymetallic mines. Our results highlight the importance of viruses in shaping the microbial community from the individual host level to the community level.

What Lies Beneath? Taking the Plunge into the Murky Waters of Phage Biology

The sequence revolution revealed that bacteria-infecting viruses, known as phages, are Earth's most abundant biological entities. Phages have far-reaching impacts on the form and function of microbial communities and play a fundamental role in ecological processes. However, even well into the sequencing revolution, we have only just begun to explore the murky waters around the phage biology iceberg. Many viral reads cannot be assigned to a culturable isolate, and reference databases are biased toward more easily collectible samples, which likely distorts our conclusions. This minireview points out alternatives to mapping reads to reference databases and highlights innovative bioinformatic and experimental approaches that can help us overcome some of the challenges in phage research and better decipher the impact of phages on microbial communities. Moving beyond the identification of novel phages, we highlight phage metabolomics as an important influencer of bacterial host cell physiology and hope to inspire the reader to consider the effects of phages on host metabolism and ecosystems at large. We encourage researchers to report unassigned/unknown sequencing reads and contigs and to continue developing alternative methods to investigate phages within sequence data.

Characterizing prophages in the genus Fusobacterium

OBJECTIVES

We set out to identify and characterize prophages within genomes of published Fusobacterium strains, and to develop qPCR-based methods to characterize intra- and extra-cellular induction of prophage replication in a variety of environmental contexts.

METHODS

Various in silico tools were used to predict prophage presence across 105 Fusobacterium spp. Genomes. Using the example of the model pathogen, Fusobacterium nucleatum subsp. animalis strain 7-1, qPCR was used with DNase I treatment to determine induction of its 3 predicted prophages ɸFunu1, ɸFunu2, and ɸFunu3, across several conditions.

RESULTS

116 predicted prophage sequences were found and analyzed. An emerging association between the phylogenetic history of a Fusobacterium prophage and that of its host was detected, as was the presence of genes encoding putative host fitness factors (e.g. ADP-ribosyltransferases) in distinct subclusters of prophage genomes. For strain 7-1, a pattern of expression for ɸFunu1, ɸFunu2, and ɸFunu3 was established indicating that ɸFunu1 and ɸFunu2 are capable of spontaneous induction. I Salt and mitomycin C exposure were able to promote induction of ɸFunu2. A range of other biologically relevant stressors, including exposure to pH, mucin and human cytokines showed no or minimal induction of these same prophages. ɸFunu3 induction was not detected under tested conditions.

CONCLUSION

The heterogeneity of Fusobacterium strains is matched by their prophages. While the role of Fusobacterium prophages in host pathogenicity remains unclear, this work provides the first overview of clustered prophage distribution among this enigmatic genus and describes an effective assay for quantifying mixed samples of prophages that cannot be detected by plaque assay.

Diversity and potential functional characteristics of phage communities colonizing microplastic biofilms

The multiple ecological influences and potential microbial degradation of microplastics are generally attributed to the microbial communities colonized on microplastics. Phages play an important role in the composition and function of their bacterial hosts, yet the occurrence and the potential functional characteristics of phages in the biofilms of microplastics have not been known. This study, for the first time, explored the diversity, composition, and potential function characteristics of phage communities living in the biofilms of PP, PE, and PET microplastics and stones, cultured in the same site, via the metagenome method. The results showed that a total of 240 non-redundant virus OTUs (vOTUs), distributed in at least four orders and seven families, were detected from biofilm metagenomes of microplastics. Compared to stones, some phages were selectively enriched by microplastic biofilms, with 13 vOTUs uniquely colonized on three microplastics, and these vOTUs mainly belong to the family Autographiviridae and Podoviridae. Except for the evenness of PP, the richness index, Chao 1 index, and abundance of phage communities of three microplastics were much higher than that of stone. At least 8 bacterial phyla and 72 genera were possibly infected by phages. Compared to the stones, both composition and abundance of the phages and hosts presented significant and strong correlations for three microplastics. Some of the bacterial hosts on microplastics were likely involved in the microplastic degradation, fermenters, nitrogen transformation processes, and so on. A total of 124 encoding auxiliary metabolic genes (AMGs) were detected from viral contigs. The abundance of AMGs in microplastics was much higher than that of stones, which may provide more direct or indirect support for the bacterial degradation of microplastics. This study provides a new perspective on the occurrence and potential functions of phages on microplastic biofilms, thus expanding our understanding of microbial communities on microplastic biofilms.

When Plaquing Is Not Possible: Computational Methods for Detecting Induced Phages

High-throughput sequencing of microbial communities has uncovered a large, diverse population of phages. Frequently, phages found are integrated into their bacterial host genome. Distinguishing between phages in their integrated (lysogenic) and unintegrated (lytic) stage can provide insight into how phages shape bacterial communities. Here we present the Prophage Induction Estimator (PIE) to identify induced phages in genomic and metagenomic sequences. PIE takes raw sequencing reads and phage sequence predictions, performs read quality control, read assembly, and calculation of phage and non-phage sequence abundance and completeness. The distribution of abundances for non-phage sequences is used to predict induced phages with statistical confidence. In silico tests were conducted to benchmark this tool finding that PIE can detect induction events as well as phages with a relatively small burst size (10×). We then examined isolate genome sequencing data as well as a mock community and urinary metagenome data sets and found instances of induced phages in all three data sets. The flexibility of this software enables users to easily include phage predictions from their preferred tool of choice or phage sequences of interest. Thus, genomic and metagenomic sequencing now not only provides a means for discovering and identifying phage sequences but also the detection of induced prophages.

Disarm The Bacteria: What Temperate Phages Can Do

In the field of phage applications and clinical treatment, virulent phages have been in the spotlight whereas temperate phages received, relatively speaking, less attention. The fact that temperate phages often carry virulent or drug-resistant genes is a constant concern and drawback in temperate phage applications. However, temperate phages also play a role in bacterial regulation. This review elucidates the biological properties of temperate phages based on their life cycle and introduces the latest work on temperate phage applications, such as on host virulence reduction, biofilm degradation, genetic engineering and phage display. The versatile use of temperate phages coupled with their inherent properties, such as economy, ready accessibility, wide variety and host specificity, make temperate phages a solid candidate in tackling bacterial infections.

The Emerging Role of the Gut Virome in Health and Inflammatory Bowel Disease: Challenges, Covariates and a Viral Imbalance

Virome research is a rapidly growing area in the microbiome field that is increasingly associated with human diseases, such as inflammatory bowel disease (IBD). Although substantial progress has been made, major methodological challenges limit our understanding of the virota. In this review, we describe challenges that must be considered to accurately report the virome composition and the current knowledge on the virome in health and IBD. First, the description of the virome shows strong methodological biases related to wetlab (e.g., VLP enrichment) and bioinformatics approaches (viral identification and classification). Second, IBD patients show consistent viral imbalances characterized by a high relative abundance of phages belonging to the Caudovirales and a low relative abundance of phages belonging to the Microviridae. Simultaneously, a sporadic contraction of CrAss-like phages and a potential expansion of the lysogenic potential of the intestinal virome are observed. Finally, despite numerous studies that have conducted diversity analysis, it is difficult to draw firm conclusions due to methodological biases. Overall, we present the many methodological and environmental factors that influence the virome, its current consensus in health and IBD, and a contributing hypothesis called the "positive inflammatory feedback loop" that may play a role in the pathophysiology of IBD.

Mapping the early life gut microbiome in neonates with critical congenital heart disease: multiomics insights and implications for host metabolic and immunological health

BACKGROUND

The early life gut microbiome is crucial in maintaining host metabolic and immune homeostasis. Though neonates with critical congenital heart disease (CCHD) are at substantial risks of malnutrition and immune imbalance, the microbial links to CCHD pathophysiology remain poorly understood. In this study, we aimed to investigate the gut microbiome in neonates with CCHD in association with metabolomic traits. Moreover, we explored the clinical implications of the host-microbe interactions in CCHD.

METHODS

Deep metagenomic sequencing and metabolomic profiling of paired fecal samples from 45 neonates with CCHD and 50 healthy controls were performed. The characteristics of gut microbiome were investigated in three dimensions (microbial abundance, functionality, and genetic variation). An in-depth analysis of gut virome was conducted to elucidate the ecological interaction between gut viral and bacterial communities. Correlations between multilevel microbial features and fecal metabolites were determined using integrated association analysis. Finally, we conducted a subgroup analysis to examine whether the interactions between gut microbiota and metabolites could mediate inflammatory responses and poor surgical prognosis.

RESULTS

Gut microbiota dysbiosis was observed in neonates with CCHD, characterized by the depletion of Bifidobacterium and overgrowth of Enterococcus, which was highly correlated with metabolomic perturbations. Genetic variations of Bifidobacterium and Enterococcus orchestrate the metabolomic perturbations in CCHD. A temperate core virome represented by Siphoviridae was identified to be implicated in shaping the gut bacterial composition by modifying microbial adaptation. The overgrowth of Enterococcus was correlated with systemic inflammation and poor surgical prognosis in subgroup analysis. Mediation analysis indicated that the overgrowth of Enterococcus could mediate gut barrier impairment and inflammatory responses in CCHD.

CONCLUSIONS

We demonstrate for the first time that an aberrant gut microbiome associated with metabolomic perturbations is implicated in immune imbalance and adverse clinical outcomes in neonates with CCHD. Our data support the importance of reconstituting optimal gut microbiome in maintaining host metabolic and immunological homeostasis in CCHD. Video Abstract.

Viral community-wide auxiliary metabolic genes differ by lifestyles, habitats, and hosts

BACKGROUND

Viral-encoded auxiliary metabolic genes (AMGs) are important toolkits for modulating their hosts' metabolisms and the microbial-driven biogeochemical cycles. Although the functions of AMGs have been extensively reported in numerous environments, we still know little about the drivers that shape the viral community-wide AMG compositions in natural ecosystems. Exploring the drivers of viral community-wide AMG compositions is critical for a deeper understanding of the complex interplays among viruses, hosts, and the environments.

RESULTS

Here, we investigated the impact of viral lifestyles (i.e., lytic and lysogenic), habitats (i.e., water, particle, and sediment), and prokaryotic hosts on viral AMG profiles by utilizing metagenomic and metatranscriptomic techniques. We found that viral lifestyles were the most important drivers, followed by habitats and host identities. Specifically, irrespective of what habitats viruses came from, lytic viruses exhibited greater AMG diversity and tended to encode AMGs for chaperone biosynthesis, signaling proteins, and lipid metabolism, which could boost progeny reproduction, whereas temperate viruses were apt to encode AMGs for host survivability. Moreover, the lytic and temperate viral communities tended to mediate the microbial-driven biogeochemical cycles, especially nitrogen metabolism, in different manners via AMGs. When focusing on each lifestyle, we further found clear dissimilarity in AMG compositions between water and sediment, as well the divergent AMGs encoded by viruses infecting different host orders.

CONCLUSIONS

Overall, our study provides a first systematic characterization of the drivers of viral community-wide AMG compositions and further expands our knowledge of the distinct interactions of lytic and temperate viruses with their prokaryotic hosts from an AMG perspective, which is critical for understanding virus-host-environment interactions in natural conditions. Video Abstract.

Phage-host interactions: The neglected part of biological wastewater treatment

In wastewater treatment plants (WWTPs), the stable operation of biological wastewater treatment is strongly dependent on the stability of associated microbiota. Bacteriophages (phages), viruses that specifically infect bacteria and archaea, are highly abundant and diverse in WWTPs. Although phages do not have known metabolic functions for themselves, they can shape functional microbiota via various phage-host interactions to impact biological wastewater treatment. However, the developments of phage-host interaction in WWTPs and their impact on biological wastewater treatment are overlooked. Here, we review the current knowledge regarding the phage-host interactions in biological wastewater treatment, mainly focusing on the characteristics of different phage populations, the phage-driven changes in functional microbiota, and the potential driving factors of phage-host interactions. We also discuss the efforts required further to understand and manipulate the phage-host interactions in biological wastewater treatment. Overall, this review advocates more attention to the phage dynamics in WWTPs.

Enterorenal crosstalks in diabetic nephropathy and novel therapeutics targeting the gut microbiota

The role of gut-kidney crosstalk in the progression of diabetic nephropathy (DN) is receiving increasing concern. On one hand, the decline in renal function increases circulating uremic toxins and affects the composition and function of gut microbiota. On the other hand, intestinal dysbiosis destroys the epithelial barrier, leading to increased exposure to endotoxins, thereby exacerbating kidney damage by inducing systemic inflammation. Dietary inventions, such as higher fiber intake, prebiotics, probiotics, postbiotics, fecal microbial transplantation (FMT), and engineering bacteria and phages, are potential microbiota-based therapies for DN. Furthermore, novel diabetic agents, such as glucagon-like peptide-1 (GLP-1) receptor agonists, dipeptidyl peptidase-4 (DPP-4) inhibitors, and sodium-dependent glucose transporter-2 (SGLT-2) inhibitors, may affect the progression of DN partly through gut microbiota. In the current review, we mainly summarize the evidence concerning the gut-kidney axis in the advancement of DN and discuss therapies targeting the gut microbiota, expecting to provide new insight into the clinical treatment of DN.

Forty Years without Family: Three Novel Bacteriophages with High Similarity to SPP1 Reveal Decades of Evolutionary Stasis since the Isolation of Their Famous Relative

SPP1, an extensively studied bacteriophage of the Gram-positive Bacillus subtilis, is a model system for the study of phage-host interactions. Despite progress in the isolation and characterization of Bacillus phages, no previously fully sequenced phages have shared more than passing genetic similarity to SPP1. Here, we describe three virulent phages very similar to SPP1; SPP1 has greater than 80% nucleotide sequence identity and shares more that 85% of its protein coding genes with these phages. This is remarkable, given more than 40 years between the isolation of SPP1 and these phages. All three phages have somewhat larger genomes and more genes than SPP1. We identified a new putative gene in SPP1 based on a conserved sequence found in all phages. Gene conservation connotes purifying selection and is observed in structural genes and genes involved in DNA metabolism, but also in genes of unknown function, suggesting an important role in phage survival independent of the environment. Patterns of divergence point to genes or gene domains likely involved in adaptation to diverse hosts or different environments. Ultimately, comparative genomics of related phages provides insight into the long-term selective pressures that affect phage-bacteria interactions and alter phage genome content.

The Life Cycle Transitions of Temperate Phages: Regulating Factors and Potential Ecological Implications

Phages are viruses that infect bacteria. They affect various microbe-mediated processes that drive biogeochemical cycling on a global scale. Their influence depends on whether the infection is lysogenic or lytic. Temperate phages have the potential to execute both infection types and thus frequently switch their infection modes in nature, potentially causing substantial impacts on the host-phage community and relevant biogeochemical cycling. Understanding the regulating factors and outcomes of temperate phage life cycle transition is thus fundamental for evaluating their ecological impacts. This review thus systematically summarizes the effects of various factors affecting temperate phage life cycle decisions in both culturable phage-host systems and natural environments. The review further elucidates the ecological implications of the life cycle transition of temperate phages with an emphasis on phage/host fitness, host-phage dynamics, microbe diversity and evolution, and biogeochemical cycles.

Intestinal virome in patients with alcohol use disorder and after abstinence

Alcohol use is a leading cause of chronic liver disease worldwide, and changes in the microbiome associated with alcohol use contribute to patients' risk for liver disease progression. Less is known about the effects of alcohol use on the intestinal viral microbiome (virome) and interactions between bacteriophages and their target bacteria. We studied changes in the intestinal virome of 62 clinically well-characterized patients with alcohol use disorder (AUD) during active alcohol use and after 2 weeks of alcohol abstinence, by extracting virus-like particles and performing metagenomic sequencing. We observed decreased abundance of Propionibacterium, Lactobacillus, and Leuconostoc phages in patients with active AUD when compared with controls, whereas after 2 weeks of alcohol abstinence, patients with AUD demonstrated an increase in the abundance of Propionibacterium, Lactobacillus, and Leuconostoc phages. The intestinal virome signature was also significantly different in patients with AUD with progressive liver disease, with increased abundance of phages targeting Enterobacteria and Lactococcus species phages compared with patients with AUD with nonprogressive liver disease. By performing moderation analyses, we found that progressive liver disease is associated with changes in interactions between some bacteriophages and their respective target bacteria. In summary, active alcohol use and alcohol-associated progressive liver disease are associated with changes in the fecal virome, some of which are partially reversible after a short period of abstinence. Progression of alcohol-associated liver disease is associated with changes in bacteriophage-bacteria interactions.

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.

Deconstructing the Phage-Bacterial Biofilm Interaction as a Basis to Establish New Antibiofilm Strategies

The bacterial biofilm constitutes a complex environment that endows the bacterial community within with an ability to cope with biotic and abiotic stresses. Considering the interaction with bacterial viruses, these biofilms contain intrinsic defense mechanisms that protect against phage predation; these mechanisms are driven by physical, structural, and metabolic properties or governed by environment-induced mutations and bacterial diversity. In this regard, horizontal gene transfer can also be a driver of biofilm diversity and some (pro)phages can function as temporary allies in biofilm development. Conversely, as bacterial predators, phages have developed counter mechanisms to overcome the biofilm barrier. We highlight how these natural systems have previously inspired new antibiofilm design strategies, e.g., by utilizing exopolysaccharide degrading enzymes and peptidoglycan hydrolases. Next, we propose new potential approaches including phage-encoded DNases to target extracellular DNA, as well as phage-mediated inhibitors of cellular communication; these examples illustrate the relevance and importance of research aiming to elucidate novel antibiofilm mechanisms contained within the vast set of unknown ORFs from phages.

Bioprospecting of Ribosomally Synthesized and Post-translationally Modified Peptides Through Genome Characterization of a Novel Probiotic Lactiplantibacillus plantarum UTNGt21A Strain: A Promising Natural Antimicrobials Factory

The present work describes the genome sequencing and characterization of a novel Lactiplantibacillus plantarum strain assigned UTNGt21A isolated from wild Solanum quitoense (L.) fruits. In silico analysis has led to identifying a wide range of biosynthetic gene clusters (BGCs) and metabolic compounds. The genome had a total of 3,558,611 bp with GC of 43.96%, harboring 3,449 protein-coding genes, among which 3,209 were assigned by the EggNOG database, and 240 hypothetical proteins have no match in the BLASTN database. It also contains 68 tRNAs, 1 23S rRNA, 1 16S rRNA, 6 5S rRNA, and 1 tmRNA. In addition, no acquired resistance genes nor virulence and pathogenic factors were predicted, indicating that UTNGt21A is a safe strain. Three areas of interest (AOI) consisting of multiple genes encoding for bacteriocins and ABC transporters were predicted with BAGEL4, while eight secondary metabolite regions were predicted with the antiSMASH web tool. GutSMASH analysis predicted one metabolic gene cluster (MGC) type pyruvate to acetate-formate, a primary metabolite region essential for anaerobe growth. Several lanthipeptides and non-ribosomal peptide synthetase (NRPS) clusters were detected in the UTNGt21A but not the reference genomes, suggesting that their genome diversity might be linked to its niche-specific lineage and adaptation to a specific environment. Moreover, the application of a targeted genome mining tool (RiPPMiner) uncovered a diverse arsenal of important antimicrobial molecules such as lanthipeptides. Furthermore, in vitro analysis indicated that the crude extract (CE) of UTNGt21A exerted a wide spectrum of inhibition against several pathogens. The results indicated that the possible peptide-protein extract (PC) from UTNGt21A induces morphological and ultrastructural changes of Salmonella enterica subsp. enterica ATCC51741, compatible with its inhibitory potential. Genome characterization is the basis for further in vitro and in vivo studies to explore their use as antimicrobial producers or probiotic strains.

The Chronic Wound Phageome: Phage Diversity and Associations with Wounds and Healing Outcomes

Two leading impediments to chronic wound healing are polymicrobial infection and biofilm formation. Recent studies have characterized the bacterial fraction of these microbiomes and have begun to elucidate compositional correlations to healing outcomes. However, the factors that drive compositional shifts are still being uncovered. The virome may play an important role in shaping bacterial community structure and function. Previous work on the skin virome determined that it was dominated by bacteriophages, viruses that infect bacteria. To characterize the virome, we enrolled 20 chronic wound patients presenting at an outpatient wound care clinic in a microbiome survey, collecting swab samples from healthy skin and chronic wounds (diabetic, venous, arterial, or pressure) before and after a single, sharp debridement procedure. We investigated the virome using a virus-like particle enrichment procedure, shotgun metagenomic sequencing, and a k-mer-based, reference-dependent taxonomic classification method. Taxonomic composition, diversity, and associations with covariates are presented. We find that the wound virome is highly diverse, with many phages targeting known pathogens, and may influence bacterial community composition and functionality in ways that impact healing outcomes.

IMPORTANCE Chronic wounds are an increasing medical burden. These wounds are known to be rich in microbial content, including both bacteria and bacterial viruses (phages). The viruses may play an important role in shaping bacterial community structure and function. We analyzed the virome and bacterial composition of 20 patients with chronic wounds. The viruses found in wounds are highly diverse compared to normal skin, unlike the bacterial composition, where diversity is decreased. These data represent an initial look at this relatively understudied component of the chronic wound microbiome and may help inform future phage-based interventions.

The gut virome in two indigenous populations from Malaysia

The human gut contains a complex microbiota dominated by bacteriophages but also containing other viruses and bacteria and fungi. There are a growing number of techniques for the extraction, sequencing, and analysis of the virome but currently no standardized protocols. This study established an effective workflow for virome analysis to investigate the virome of stool samples from two understudied ethnic groups from Malaysia: the Jakun and Jehai Orang Asli. By using the virome extraction and analysis workflow with the Oxford Nanopore Technology, long-read sequencing successfully captured close to full-length viral genomes. The virome composition of the two indigenous Malaysian communities were remarkably different from those found in other parts of the world. Additionally, plant viruses found in the viromes of these individuals were attributed to traditional food-seeking methods. This study establishes a human gut virome workflow and extends insights into the healthy human gut virome, laying the groundwork for comparative studies.

YdfD, a Lysis Protein of the Qin Prophage, Is a Specific Inhibitor of the IspG-Catalyzed Step in the MEP Pathway of Escherichia coli

Bacterial cryptic prophage (defective prophage) genes are known to drastically influence host physiology, such as causing cell growth arrest or lysis, upon expression. Many phages encode lytic proteins to destroy the cell envelope. As natural antibiotics, only a few lysis target proteins were identified. ydfD is a lytic gene from the Qin cryptic prophage that encodes a 63-amino-acid protein, the ectopic expression of which in Escherichia coli can cause nearly complete cell lysis rapidly. The bacterial 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway is responsible for synthesizing the isoprenoids uniquely required for sustaining bacterial growth. In this study, we provide evidence that YdfD can interact with IspG, a key enzyme involved in the MEP pathway, both in vivo and in vitro. We show that intact YdfD is required for the interaction with IspG to perform its lysis function and that the mRNA levels of ydfD increase significantly under certain stress conditions. Crucially, the cell lysis induced by YdfD can be abolished by the overexpression of ispG or the complementation of the IspG enzyme catalysis product methylerythritol 2,4-cyclodiphosphate. We propose that YdfD from the Qin cryptic prophage inhibits IspG to block the MEP pathway, leading to a compromised cell membrane and cell wall biosynthesis and eventual cell lysis.

Intraspecific antagonism through viral toxin encoded by chronic Sulfolobus spindle-shaped virus

Virus-host interactions evolve along a symbiosis continuum from antagonism to mutualism. Long-term associations between virus and host, such as those in chronic infection, will select for traits that drive the interaction towards mutualism, especially when susceptible hosts are rare in the population. Virus-host mutualism has been demonstrated in thermophilic archaeal populations where Sulfolobus spindle-shaped viruses (SSVs) provide a competitive advantage to their host Sulfolobus islandicus by producing a toxin that kills uninfected strains. Here, we determine the genetic basis of this killing phenotype by identifying highly transcribed genes in cells that are chronically infected with a diversity of SSVs. We demonstrate that these genes alone confer growth inhibition by being expressed in uninfected cells via a Sulfolobus expression plasmid. Challenge of chronically infected strains with vector-expressed toxins revealed a nested network of cross-toxicity among divergent SSVs, with both broad and specific toxin efficacies. This suggests that competition between viruses and/or their hosts could maintain toxin diversity. We propose that competitive interactions among chronic viruses to promote their host fitness form the basis of virus-host mutualism. This article is part of the theme issue 'The secret lives of microbial mobile genetic elements'.

Prophage Gene Rv2650c Enhances Intracellular Survival of Mycobacterium smegmatis

Background

Induced by the pathogen Mycobacterium tuberculosis, tuberculosis remains one of the most dangerous infectious diseases in the world. As a special virus, prophage is domesticated by its host and are major contributors to virulence factors for bacterial pathogenicity. The function of prophages and their genes in M. tuberculosis is still unknown.

Methods

Rv2650c is a prophage gene in M. tuberculosis genome. We constructed recombinant Mycobacterium smegmatis (M. smegmatis) to observe bacteria morphology and analyze the resistance to various adverse environments. Recombinant and control strains were used to infect macrophages, respectively. Furthermore, we performed ELISA experiments of infected macrophages.

Results

Rv2650c affected the spread of colonies of M. smegmatis and enhanced the resistance of M. smegmatis to macrophages and various stress agents such as acid, oxidative stress, and surfactant. ELISA experiments revealed that the Rv2650c can inhibit the expression of inflammatory factors TNF-α, IL-10, IL-1β, and IL-6.

Conclusion

This study demonstrates that the prophage gene Rv2650c can inhibit the spread of colonies and the expression of inflammatory factors and promote intracellular survival of M. smegmatis. These results build the foundation for the discovery of virulence factors of M. tuberculosis, and provide novel insights into the function of the prophage in Mycobacterium.

Hidden diversity of double-stranded DNA phages in symbiotic Rhizobium species

In this study, we addressed the extent of diversification of phages associated with nitrogen-fixing symbiotic Rhizobium species. Despite the ecological and economic importance of the Rhizobium genus, little is known about the diversity of the associated phages. A thorough assessment of viral diversity requires investigating both lytic phages and prophages harboured in diverse Rhizobium genomes. Protein-sharing networks identified 56 viral clusters (VCs) among a set of 425 isolated phages and predicted prophages. The VCs formed by phages had more proteins in common and a higher degree of synteny, and they group together in clades in the associated phylogenetic tree. By contrast, the VCs of prophages showed significant genetic variation and gene loss, with selective pressure on the remaining genes. Some VCs were found in various Rhizobium species and geographical locations, suggesting that they have wide host ranges. Our results indicate that the VCs represent distinct taxonomic units, probably representing taxa equivalent to genera or even species. The finding of previously undescribed phage taxa indicates the need for further exploration of the diversity of phages associated with Rhizobium species. This article is part of the theme issue 'The secret lives of microbial mobile genetic elements'.

Eukaryotic Microbial RNA Viruses-Acute or Persistent? Insights into Their Function in the Aquatic Ecosystem

Isolated RNA viruses mainly parasitize eukaryotes. RNA viruses either expand horizontally by infecting hosts (acute type) or coexist with the host and are vertically inherited (persistent type). The significance of persistent-type RNA viruses in environmental viromes (the main hosts are expected to be microbes) was only recently reported because they had previously been overlooked in virology. In this review, we summarize the host-virus relationships of eukaryotic microbial RNA viruses. Picornavirales and Reoviridae are recognized as representative acute-type virus families, and most of the microbial viruses in Narnaviridae, Totiviridae, and Partitiviridae are categorized as representative persistent-type viruses. Acute-type viruses have only been found in aquatic environments, while persistent-type viruses are present in various environments, including aquatic environments. Moreover, persistent-type viruses are potentially widely spread in the RNA viral sequence space. This emerging evidence provides novel insights into RNA viral diversity, host-virus relationships, and their history of co-evolution.

Prophage Activation in the Intestine: Insights Into Functions and Possible Applications

Prophage activation in intestinal environments has been frequently reported to affect host adaptability, pathogen virulence, gut bacterial community composition, and intestinal health. Prophage activation is mostly caused by various stimulators, such as diet, antibiotics, some bacterial metabolites, gastrointestinal transit, inflammatory environment, oxidative stress, and quorum sensing. Moreover, with advancements in biotechnology and the deepening cognition of prophages, prophage activation regulation therapy is currently applied to the treatment of some bacterial intestinal diseases such as Shiga toxin-producing Escherichia coli infection. This review aims to make headway on prophage induction in the intestine, in order to make a better understanding of dynamic changes of prophages, effects of prophage activation on physiological characteristics of bacteria and intestinal health, and subsequently provide guidance on prophage activation regulation therapy.

The bacteriophage decides own tracks: When they are with or against the bacteria

Bacteriophages, bacteria-infecting viruses, are considered by many researchers a promising solution for antimicrobial resistance. On the other hand, some phages have shown contribution to bacterial resistance phenomenon by transducing antimicrobial resistance genes to their bacterial hosts. Contradictory consequences of infections are correlated to different phage lifecycles. Out of four known lifecycles, lysogenic and lytic pathways have been riddles since the uncontrolled conversion between them could negatively affect the intended use of phages. However, phages still can be engineered for applications against bacterial and viral infections to ensure high efficiency. This review highlights two main aspects: (1) the different lifecycles as well as the different factors that affect lytic-lysogenic switch are discussed, including the intracellular and molecular factors control this decision. In addition, different models which describe the effect of phages on the ecosystem are compared, besides the approaches to study the switch. (2) An overview on the contribution of the phage in the evolution of the bacteria, instead of eating them, as a consequence of different mode of actions. As well, how phage display has helped in restricting phage cheating and how it could open new gates for immunization and pandemics control will be tacked.

Let Me Upgrade You: Impact of Mobile Genetic Elements on Enterococcal Adaptation and Evolution

Enterococci are Gram-positive bacteria that have evolved to thrive as both commensals and pathogens, largely due to their accumulation of mobile genetic elements via horizontal gene transfer (HGT). Common agents of HGT include plasmids, transposable elements, and temperate bacteriophages. These vehicles of HGT have facilitated the evolution of the enterococci, specifically Enterococcus faecalis and Enterococcus faecium, into multidrug-resistant hospital-acquired pathogens. On the other hand, commensal strains of Enterococcus harbor CRISPR-Cas systems that prevent the acquisition of foreign DNA, restricting the accumulation of mobile genetic elements. In this review, we discuss enterococcal mobile genetic elements by highlighting their contributions to bacterial fitness, examine the impact of CRISPR-Cas on their acquisition, and identify key areas of research that can improve our understanding of enterococcal evolution and ecology.

Prophage Tracer: precisely tracing prophages in prokaryotic genomes using overlapping split-read alignment

The life cycle of temperate phages includes a lysogenic cycle stage when the phage integrates into the host genome and becomes a prophage. However, the identification of prophages that are highly divergent from known phages remains challenging. In this study, by taking advantage of the lysis-lysogeny switch of temperate phages, we designed Prophage Tracer, a tool for recognizing active prophages in prokaryotic genomes using short-read sequencing data, independent of phage gene similarity searching. Prophage Tracer uses the criterion of overlapping split-read alignment to recognize discriminative reads that contain bacterial (attB) and phage (attP) att sites representing prophage excision signals. Performance testing showed that Prophage Tracer could predict known prophages with precise boundaries, as well as novel prophages. Two novel prophages, dsDNA and ssDNA, encoding highly divergent major capsid proteins, were identified in coral-associated bacteria. Prophage Tracer is a reliable data mining tool for the identification of novel temperate phages and mobile genetic elements. The code for the Prophage Tracer is publicly available at https://github.com/WangLab-SCSIO/Prophage_Tracer.