Phages rarely encode antibiotic resistance genes: a cautionary tale for virome analyses

Phage Genome Annotation: Where to Begin and End

With the renewed interest in phage research, coupled with the rising accessibility to affordable sequencing, ever increasing numbers of phage genomes are being sequenced. Therefore, there is an increased need to assemble and annotate phage genomes. There is a plethora of tools and platforms that allow phage genomes to be assembled and annotated. The choice of tools can often be bewildering for those new to phage genome assembly. Here we provide an overview of the assembly and annotation process from obtaining raw reads to genome submission, with worked examples, providing those new to genome assembly and annotation with a guided pathway to genome submission. We focus on the use of open access tools that can be incorporated into workflows to allow easy repetition of steps, highlighting multiple tools that can be used and common pitfalls that may occur.

Uses of Bacteriophages as Bacterial Control Tools and Environmental Safety Indicators

Bacteriophages are bacterial-specific viruses and the most abundant biological form on Earth. Each bacterial species possesses one or multiple bacteriophages and the specificity of infection makes them a promising alternative for bacterial control and environmental safety, as a biotechnological tool against pathogenic bacteria, including those resistant to antibiotics. This application can be either directly into foods and food-related environments as biocontrol agents of biofilm formation. In addition, bacteriophages are used for microbial source-tracking and as fecal indicators. The present review will focus on the uses of bacteriophages like bacterial control tools, environmental safety indicators as well as on their contribution to bacterial control in human, animal, and environmental health.

A 'time bomb' in the human intestine-the multiple emergence and spread of antibiotic-resistant bacteria

Antibiotics have a strong killing effect on bacteria and are the first choice for the prevention and treatment of bacterial infectious diseases. Therefore, they have been widely used in the medical field, animal husbandry and planting industry. However, with the massive use of antibiotics, more and more antibiotic-resistant bacteria (ARB) have emerged. Because human intestines are rich in nutrients, have suitable temperature, and are high in bacterial abundance, they can easily become a hotbed for the spread of ARB and antibiotic-resistant genes (ARGs). When opportunistic pathogenic bacteria in the intestine acquire ARGs, the infectious diseases caused by such opportunistic pathogens will become more difficult to treat, or even impossible to cure. Therefore, ARB in the human intestine are like a 'time bomb'. In this review, we discuss the sources of intestinal ARB and the transmission routes of ARGs in the human intestine from the perspective of One Health. Further, we describe various methods to prevent the emergence of ARB and inhibit the spread of ARGs in the human intestine. Finally, we may be able to overcome ARB in the human intestine using an interdisciplinary 'One Health' approach.

Metagenomics of wastewater phageome identifies an extensively cored antibiotic resistome in a swine feedlot water treatment environment

Huge number of antibiotic resistance genes (ARGs) have been widely detected in phage genomes from anthropogenic environment or animal farms, whereas little is known about the dynamic changes of phage contribution to resistance under a feedlot wastewater treatment facility (WTF) pressure. Here, a metagenomics method was used to characterize the sewage phageome and identifies the antibiotic resistome. The results showed that the phage families of Siphoviridae, Myoviridae, and Podoviridae were always the most dominant. Analysis of ARGs carried by bacterial and phages showed that MLS and tetracycline resistance genes always had the highest abundances and the other ARG types also have a fixed hierarchy, showing that there is no significant change in overall ARGs abundance distribution. However, an extensively cored antibiotic resistome were specifically identified in aerobic environment. ARGs encoding ribosomal protection proteins, especially for the ARG subtypes lsaE, tet44, tetM, tetP, macB, MdlB and rpoB2, were more inclined to be selected by phages, suggesting that a more refined mechanism, such as specialized transduction and lateral transduction, was probably involved. In all, these results suggest that monitoring of dynamic changes of phage contribution to resistance should be given more attention and ARGs-carrying phage management should focus on using technologies for controlling cored ARGs rather than only the overall distribution of ARGs in phages.

Genomic Sequence Analysis of Methicillin- and Carbapenem-Resistant Bacteria Isolated from Raw Sewage

Antibiotic resistance is one of the largest threats facing global health. Wastewater treatment plants are well-known hot spots for interaction between diverse bacteria, genetic exchange, and antibiotic resistance. Nonpathogenic bacteria theoretically act as reservoirs of antibiotic resistance subsequently transferring antibiotic resistance genes to pathogens, indicating that evolutionary processes occur outside clinical settings and may drive patterns of drug-resistant infections. We isolated and sequenced 100 bacterial strains from five wastewater treatment plants to analyze regional dynamics of antibiotic resistance in the California Central Valley. The results demonstrate the presence of a wide diversity of pathogenic and nonpathogenic bacteria, with an arithmetic mean of 5.1 resistance genes per isolate. Forty-three percent of resistance genes were located on plasmids, suggesting that large levels of gene transfer between bacteria that otherwise may not co-occur are facilitated by wastewater treatment. One of the strains detected was a Bacillus carrying pX01 and pX02 anthrax-like plasmids and multiple drug resistance genes. A correlation between resistance genes and taxonomy indicates that taxon-specific evolutionary studies may be useful in determining and predicting patterns of antibiotic resistance. Conversely, a lack of geographic correlation may indicate that landscape genetic studies to understand the spread of antibiotic resistance genes should be carried out at broader scales. This large data set provides insights into how pathogenic and nonpathogenic bacteria interact in wastewater environments and the resistance genes which may be horizontally transferred between them. This can help in determining the mechanisms leading to the increasing prevalence of drug-resistant infections observed in clinical settings. IMPORTANCE The reasons for the increasing prevalence of antibiotic-resistant infections are complex and associated with myriad clinical and environmental processes. Wastewater treatment plants operate as nexuses of bacterial interaction and are known hot spots for genetic exchange between bacteria, including antibiotic resistance genes. We isolated and sequenced 100 drug-resistant bacteria from five wastewater treatment plants in California's Central Valley, characterizing widespread gene sharing between pathogens and nonpathogens. We identified a novel, multiresistant Bacillus carrying anthrax-like plasmids. This empirical study supports the likelihood of evolutionary and population processes in the broader environment affecting the prevalence of clinical drug-resistant infections and identifies several taxa that may operate as reservoirs and vectors of antibiotic resistance genes.

A genome guided evaluation of the Lab4 probiotic consortium

In this study, we present the draft genome sequences of the Lab4 probiotic consortium using whole genome sequencing. Draft genome sequences were retrieved and deposited for each of the organisms; PRJNA559984 for B. bifidum CUL20, PRJNA482335 for Lactobacillus acidophilus CUL60, PRJNA482434 for Lactobacillus acid. Probiogenomic in silico analyses confirmed existing taxonomies and identified the presence putative gene sequences that were functionally related to the performance of each organism during in vitro assessments of bile and acid tolerability, adherence to enterocytes and susceptibility to antibiotics. Predictions of genomic stability identified no significant risk of horizontal gene transfer in any of the Lab4 strains and the absence of both antibiotic resistance and virulence genes. These observations were supported by the outcomes of acute phase and repeat dose tolerability studies in Wistar rats where challenge with high doses of Lab4 did not result in any mortalities, clinical/histopathological abnormalities nor indications of systemic toxicity. Detection of increased numbers of lactobacilli and bifidobacteria in the faeces of supplemented rats implied an ability to survive transit through the gastrointestinal tract and/or impact upon the intestinal microbiota composition. In summary, this study provides in silico, in vitro and in vivo support for probiotic functionality and the safety of the Lab4 consortium.

Interactions between bacterial and phage communities in natural environments

We commonly acknowledge that bacterial viruses (phages) shape the composition and evolution of bacterial communities in nature and therefore have important roles in ecosystem functioning. This view stems from studies in the 1990s to the first decade of the twenty-first century that revealed high viral abundance, high viral diversity and virus-induced microbial death in aquatic ecosystems as well as an association between collapses in bacterial density and peaks in phage abundance. The recent surge in metagenomic analyses has provided deeper insight into the abundance, genomic diversity and spatio-temporal dynamics of phages in a wide variety of ecosystems, ranging from deep oceans to soil and the mammalian digestive tract. However, the causes and consequences of variations in phage community compositions remain poorly understood. In this Review, we explore current knowledge of the composition and evolution of phage communities, as well as their roles in controlling the population and evolutionary dynamics of bacterial communities. We discuss the need for greater ecological realism in laboratory studies to capture the complexity of microbial communities that thrive in natural environments.

More diversified antibiotic resistance genes in chickens and workers of the live poultry markets

BACKGROUND

Poultry farms and LPMs are a reservoir of antimicrobial resistant bacteria and resistance genes from feces. The LPM is an important interface between humans, farm animals, and environments in a typical urban environment, and it is considered a reservoir for ARGs and viruses. However, the antibiotic resistomes shared between chicken farms and LPMs, and that of LPM workers and people who have no contact with the LPMs remains unknown.

METHODS

We characterized the resistome and bacterial microbiome of farm chickens and LPMs and LPM workers and control subjects. The mobile ARGs identified in chickens and the distribution of the mcr-family genes in publicly bacterial genomes and chicken gut metagenomes was analyzed, respectively. In addition, the prevalence of mcr-1 in LPMs following the ban on colistin-positive additives in China was explored.

RESULTS

By profiling the microbiomes and resistomes in chicken farms, LPMs, LPM workers, and LPM environments, we found that the bacterial community composition and resistomes were significantly different between the farms and the LPMs, and the LPM samples possessed more diversified ARGs (59 types) than the farms. Some mobile ARGs, such as mcr-1 and tet(X3), identified in chicken farms, LPMs, LPM workers, and LPM environments were also harbored by human clinical pathogens. Moreover, we found that the resistomes were significantly different between the LPM workers and those who have no contact with the LPMs, and more diversified ARGs (188 types) were observed in the LPM workers. It is also worth noting that mcr-10 was identified in both human (5.2%, 96/1,859) and chicken (1.5%, 14/910) gut microbiomes. Although mcr-1 prevalence decreased significantly in the LPMs across the eight provinces in China, from 190/333 (57.1%) samples in September 2016-March 2017 to 208/544 (38.2%) samples in August 2018-May 2019, it is widespread and continuous in the LPMs.

CONCLUSION

Live poultry trade has a significant effect on the diversity of ARGs in LPM workers, chickens, and environments in China, driven by human selection with the live poultry trade. Our findings highlight the live poultry trade as ARG disseminators into LPMs, which serve as an interface of LPM environments even LPM workers, and that could urge Government to have better control of LPMs in China. Further studies on the factors that promote antibiotic resistance exchange between LPM environments, human commensals, and pathogens, are warranted.

Illuminating the Virosphere Through Global Metagenomics

Viruses are the most abundant biological entity on Earth, infect cellular organisms from all domains of life, and are central players in the global biosphere. Over the last century, the discovery and characterization of viruses have progressed steadily alongside much of modern biology. In terms of outright numbers of novel viruses discovered, however, the last few years have been by far the most transformative for the field. Advances in methods for identifying viral sequences in genomic and metagenomic datasets, coupled to the exponential growth of environmental sequencing, have greatly expanded the catalog of known viruses and fueled the tremendous growth of viral sequence databases. Development and implementation of new standards, along with careful study of the newly discovered viruses, have transformed and will continue to transform our understanding of microbial evolution, ecology, and biogeochemical cycles, leading to new biotechnological innovations across many diverse fields, including environmental, agricultural, and biomedical sciences.

Mobile Genetic Elements of Vibrio cholerae and the Evolution of Its Antimicrobial Resistance

Vibrio cholerae (VC) is the causative agent of the severe dehydrating diarrheal disease cholera. The primary treatment for cholera is oral rehydration therapy (ORT). However, in case of moderate to severe dehydration, antibiotics are administered to reduce morbidity. Due to the emergence of multidrug resistant (MDR) strains of VC routinely used antibiotics fail to be effective in cholera patients. Antimicrobial resistance (AMR) is encoded in the genome of bacteria and is usually acquired from other organisms cohabiting in the environment or in the gut with which it interacts in the gut or environmental niche. The antimicrobial resistance genes (ARGs) are usually borne on mobile genetic elements (MGEs) like plasmids, transposons, integrons and SXT constin. Horizontal gene transfer (HGT) helps in the exchange of ARGs among bacteria leading to dissemination of AMR. In VC the acquisition and loss of AMR to many antibiotics have been found to be a dynamic process. This review describes the different AMR determinants and mechanisms of resistance that have been discovered in VC. These ARGs borne usually on MGEs have been recovered from isolates associated with past and present epidemics worldwide. These are responsible for resistance of VC to common antibiotics and are periodically lost and gained contributing to its genetic evolution. These resistance markers can be routinely used for AMR surveillance in VC. The review also presents a precise perspective on the importance of the gut microbiome in the emergence of MDR VC and concludes that the gut microbiome is a potential source of molecular markers and networks which can be manipulated for the interception of AMR in the future.

Distribution of Antimicrobial Resistance and Virulence Genes within the Prophage-Associated Regions in Nosocomial Pathogens

Prophages are often involved in host survival strategies and contribute toward increasing the genetic diversity of the host genome. Prophages also drive horizontal propagation of various genes as vehicles. However, there are few retrospective studies contributing to the propagation of antimicrobial resistance (AMR) and virulence factor (VF) genes by prophage. We extracted the complete genome sequences of seven pathogens, including ESKAPE bacteria and Escherichia coli from a public database, and examined the distribution of both the AMR and VF genes in prophage-like regions. We found that the ratios of AMR and VF genes greatly varied among the seven species. More than 70% of Enterobacter cloacae strains had VF genes, but only 1.2% of Klebsiella pneumoniae strains had VF genes from prophages. AMR and VF genes are unlikely to exist together in the same prophage region except in E. coli and Staphylococcus aureus, and the distribution patterns of prophage types containing AMR genes are distinct from those of VF gene-carrying prophage types. AMR genes in the prophage were located near transposase and/or integrase. The prophage containing class 1 integrase possessed a significantly greater number of AMR genes than did prophages with no class 1 integrase. The results of this study present a comprehensive picture of AMR and VF genes present within, or close to, prophage-like elements and different prophage patterns between AMR- or VF-encoding prophage-like elements.

IMPORTANCE Although we believe phages play an important role in horizontal gene transfer in exchanging genetic material, we do not know the distribution of the antimicrobial resistance (AMR) and/or virulence factor (VF) genes in prophages. We collected different prophage elements from the complete genome sequences of seven species—Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter cloacae, and Escherichia coli—and characterized the distribution of antimicrobial resistance and virulence genes located in the prophage region. While virulence genes in prophage were species specific, antimicrobial resistance genes in prophages were highly conserved in various species. An integron structure was detected within specific prophage regions such as P1-like prophage element. Maximum of 10 antimicrobial resistance genes were found in a single prophage region, suggesting that prophages act as a reservoir for antimicrobial resistance genes. The results of this study show the different characteristic structures between AMR- or VF-encoding prophages.

Alterations, Interactions, and Diagnostic Potential of Gut Bacteria and Viruses in Colorectal Cancer

Gut microbiome alteration was closely associated with colorectal cancer (CRC). Previous studies had demonstrated the bacteria composition changes but lacked virome profiles, trans-kindom interactions, and reliable diagnostic model explorations in CRC. Hence, we performed metagenomic sequencing to investigate the gut microbiome and microbial interactions in adenoma and CRC patients. We found the decreased microbial diversity in CRC and revealed the taxonomic alterations of bacteria and viruses were highly associated with CRC at the species level. The relative abundance of oral-derived species, such as Fusobacterium nucleatum, Fusobacterium hwasookii, Porphyromonas gingivalis, and Bacteroides fragilis, increased. At the same time, butyrate-producing and anti-inflammatory microbes decreased in adenoma and CRC by non-parametric Kruskal-Wallis test. Despite that, the relative abundance of Escherichia viruses and Salmonella viruses increased, whereas some phages, including Enterobacteria phages and Uncultured crAssphage, decreased along with CRC development. Gut bacteria was negatively associated with viruses in CRC and healthy control by correlation analysis (P=0.017 and 0.002, respectively). Viruses were much more dynamic than the bacteria as the disease progressed, and the altered microbial interactions were distinctively stage-dependent. The degree centrality of microbial interactions decreased while closeness centrality increased along with the adenoma to cancer development. Uncultured crAssphage was the key bacteriophage that enriched in healthy controls and positively associated with butyrate-producing bacteria. Diagnostic tests based on bacteria by random forest confirmed in independent cohorts showed better performance than viruses for CRC. In conclusion, our study revealed the novel CRC-associated bacteria and viruses that exhibited specific differences and intensive microbial correlations, which provided a reliable diagnostic panel for CRC.

Ancient saltern metagenomics: tracking changes in microbes and their viruses from the underground to the surface

Microbial communities in hypersaline underground waters derive from ancient organisms trapped within the evaporitic salt crystals and are part of the poorly known subterranean biosphere. Here, we characterized the viral and prokaryotic assemblages present in the hypersaline springs that dissolve Triassic-Keuper evaporite rocks and feed the Añana Salt Valley (Araba/Alava, Basque Country, Spain). Four underground water samples (around 23% total salinity) with different levels of exposure to the open air were analysed by means of microscopy and metagenomics. Cells and viruses in the spring water had lower concentrations than what are normally found in hypersaline environments and seemed to be mostly inactive. Upon exposure to the open air, there was an increase in activity of both cells and viruses as well as a selection of phylotypes. The underground water was inhabited by a rich community harbouring a diverse set of genes coding for retinal binding proteins. A total of 35 viral contigs from 15 to 104 kb, representing partial or total viral genomes, were assembled and their evolutionary changes through the spring system were followed by SNP analysis and metagenomic island tracking. Overall, both the viral and the prokaryotic assemblages changed quickly upon exposure to the open air conditions.

Metagenomic and viromic data mining reveals viral threats in biologically treated domestic wastewater

Activated sludge (AS), a common biological secondary treatment process in wastewater treatment plants (WWTPs), is known to remove a large spectrum of microorganisms. Yet little is known about its effect on the entire viral community. After compiling 3 Tbp of next-generation sequencing (NGS) metagenomic/viromic datasets consisted of 119 sub-datasets of influent, effluent, and AS samples from 27 WWTPs, viral removal efficacy is evaluated through data mining. The normalized abundance of viruses suggests effluents exhibit the highest viral prevalence (3.21 ± 3.26%, n = 13) followed by the AS (0.48 ± 0.25%, n = 57) and influents (0.23 ± 0.17%, n = 17). In contrast, plasmids, representing genetic element of bacteria, show higher average prevalence (0.73 ± 0.82%, n = 17) in influents than those of the AS (0.63 ± 0.26%, n = 57) and effluents (0.35 ± 0.42%, n = 13). Furthermore, the abundance-occupancy analysis identifies 142 core phage viruses and 17 non-phages core viruses, including several pathogenic viruses in the AS virome. The persistent occurrence of pathogenic viruses, coupled with non-favorable virus removal by the AS treatment, reveals the hidden virus threats in biologically treated domestic wastewater. The mechanisms for why viruses persist and the possibility that WWTPs are potential hotspots for viral survival deserve attention.

Distribution of antibiotic resistance genes and their association with bacteria and viruses in decentralized sewage treatment facilities

The distribution of antibiotic resistance genes (ARGs) has been intensively studied in large-scale wastewater treatment plants and livestock sources. However, small-scale decentralized sewage treatment facilities must also be explored due to their possible direct exposure to residents. In this study, six wastewater treatment facilities in developed rural areas in eastern China were investigated to understand their risks of spreading ARGs. Using metagenomics and network analysis tools, ARGs and bacterial and viral communities were identified in the influent (INF) and effluent (EFF) samples. The dominant ARGs belonged to the bacitracin class, which are different from most of municipal wastewater treatment plants (WWTPs). The dominant hosts of ARGs are Acidovorax in bacterial communities and Prymnesiovirus in viral communities. Furthermore, a positive relationship was found between ARGs and phages. The ARGs significantly correlated with phages were all hosted by specific genera of bacteria, indicating that phages had contributed to the ARG's proliferation in sewage treatment facilities. Paying significant concern on the possible enhanced risks caused by bacteria, viruses and their related ARGs in decentralized sewage treatment facilities is necessary.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material is available in the online version of this article at 10.1007/s11783-021-1469-4 and is accessible for authorized users.

The landscape of lysogeny across microbial community density, diversity and energetics

Lysogens are common at high bacterial densities, an observation that contrasts with the prevailing view of lysogeny as a low-density refugium strategy. Here, we review the mechanisms regulating lysogeny in complex communities and show that the additive effects of coinfections, diversity and host energic status yield a bimodal distribution of lysogeny as a function of microbial densities. At high cell densities (above 10⁶  cells ml^-1 or g^-1 ) and low diversity, coinfections by two or more phages are frequent and excess energy availability stimulates inefficient metabolism. Both mechanisms favour phage integration and characterize the Piggyback-the-Winner dynamic. At low densities (below 10⁵  cells ml^-1 or g^-1 ), starvation represses lytic genes and extends the time window for lysogenic commitment, resulting in a higher frequency of coinfections that cause integration. This pattern follows the predictions of the refugium hypothesis. At intermediary densities (between 10⁵ and 10⁶  cells ml^-1 or g^-1 ), encounter rates and efficient energy metabolism favour lysis. This may involve Kill-the-Winner lytic dynamics and induction. Based on these three regimes, we propose a framework wherein phage integration occurs more frequently at both ends of the host density gradient, with distinct underlying molecular mechanisms (coinfections and host metabolism) dominating at each extreme.

Expanding standards in viromics: in silico evaluation of dsDNA viral genome identification, classification, and auxiliary metabolic gene curation

BACKGROUND

Viruses influence global patterns of microbial diversity and nutrient cycles. Though viral metagenomics (viromics), specifically targeting dsDNA viruses, has been critical for revealing viral roles across diverse ecosystems, its analyses differ in many ways from those used for microbes. To date, viromics benchmarking has covered read pre-processing, assembly, relative abundance, read mapping thresholds and diversity estimation, but other steps would benefit from benchmarking and standardization. Here we use in silico-generated datasets and an extensive literature survey to evaluate and highlight how dataset composition (i.e., viromes vs bulk metagenomes) and assembly fragmentation impact (i) viral contig identification tool, (ii) virus taxonomic classification, and (iii) identification and curation of auxiliary metabolic genes (AMGs).

RESULTS

The in silico benchmarking of five commonly used virus identification tools show that gene-content-based tools consistently performed well for long (≥3 kbp) contigs, while k-mer- and blast-based tools were uniquely able to detect viruses from short (≤3 kbp) contigs. Notably, however, the performance increase of k-mer- and blast-based tools for short contigs was obtained at the cost of increased false positives (sometimes up to ∼5% for virome and ∼75% bulk samples), particularly when eukaryotic or mobile genetic element sequences were included in the test datasets. For viral classification, variously sized genome fragments were assessed using gene-sharing network analytics to quantify drop-offs in taxonomic assignments, which revealed correct assignations ranging from ∼95% (whole genomes) down to ∼80% (3 kbp sized genome fragments). A similar trend was also observed for other viral classification tools such as VPF-class, ViPTree and VIRIDIC, suggesting that caution is warranted when classifying short genome fragments and not full genomes. Finally, we highlight how fragmented assemblies can lead to erroneous identification of AMGs and outline a best-practices workflow to curate candidate AMGs in viral genomes assembled from metagenomes.

CONCLUSION

Together, these benchmarking experiments and annotation guidelines should aid researchers seeking to best detect, classify, and characterize the myriad viruses 'hidden' in diverse sequence datasets.

The Human Gut Phageome: Origins and Roles in the Human Gut Microbiome

The investigation of the microbial populations of the human body, known as the microbiome, has led to a revolutionary field of science, and understanding of its impacts on human development and health. The majority of microbiome research to date has focussed on bacteria and other kingdoms of life, such as fungi. Trailing behind these is the interrogation of the gut viruses, specifically the phageome. Bacteriophages, viruses that infect bacterial hosts, are known to dictate the dynamics and diversity of bacterial populations in a number of ecosystems. However, the phageome of the human gut, while of apparent importance, remains an area of many unknowns. In this paper we discuss the role of bacteriophages within the human gut microbiome. We examine the methods used to study bacteriophage populations, how this evolved over time and what we now understand about the phageome. We review the phageome development in infancy, and factors that may influence phage populations in adult life. The role and action of the phageome is then discussed at both a biological-level, and in the broader context of human health and disease.

Comprehensive Scanning of Prophages in Lactobacillus: Distribution, Diversity, Antibiotic Resistance Genes, and Linkages with CRISPR-Cas Systems

Prophage integration, release, and dissemination exert various effects on host bacteria. In the genus Lactobacillus, they may cause bacteriophage contamination during fermentation and even regulate bacterial populations in the gut. However, little is known about their distribution, genetic architecture, and relationships with their hosts. Here, we conducted prophage prediction analysis on 1,472 genomes from 16 different Lactobacillus species and found prophage fragments in almost all lactobacilli (99.8%), with 1,459 predicted intact prophages identified in 64.1% of the strains. We present an uneven prophage distribution among Lactobacillus species; multihabitat species retained more prophages in their genomes than restricted-habitat species. Characterization of the genome features, average nucleotide identity, and landscape visualization presented a high genome diversity of Lactobacillus prophages. We detected antibiotic resistance genes in more than 10% of Lactobacillus prophages and validated that the occurrence of resistance genes conferred by prophage integration was possibly associated with phenotypic resistance in Lactobacillus plantarum. Furthermore, our broad and comprehensive examination of the distribution of CRISPR-Cas systems across the genomes predicted type I and type III systems as potential antagonistic elements of Lactobacillus prophage.

IMPORTANCE Lactobacilli are inherent microorganisms in the human gut and are widely used in the food processing industries due to their probiotic properties. Prophages were reportedly hidden in numerous Lactobacillus genomes and can potentially contaminate entire batches of fermentation or modulate the intestinal microecology once they are released. Therefore, a comprehensive scanning of prophages in Lactobacillus is essential for the safety evaluation and application development of probiotic candidates. We show that prophages are widely distributed among lactobacilli; however, intact prophages are more common in multihabitat species and display wide variations in genome feature, integration site, and genomic organization. Our data of the prophage-mediated antibiotic resistance genes (ARGs) and the resistance phenotype of lactobacilli provide evidence for deciphering the putative role of prophages as vectors of the ARGs. Furthermore, understanding the association between prophages and CRISPR-Cas systems is crucial to appreciate the coevolution of phages and Lactobacillus.

Unveiling the Impact of Antibiotics and Alternative Methods for Animal Husbandry: A Review

Since the 1950s, antibiotics have been used in the field of animal husbandry for growth promotion, therapy and disease prophylaxis. It is estimated that up to 80% of the antibiotics produced by the pharmaceutical industries are used in food production. Most of the antibiotics are used as feed additives at sub-therapeutic levels to promote growth. However, studies show the indiscriminate use of antibiotics has led to the emergence of multidrug-resistant pathogens that threaten both animal health and human health, including vancomycin-resistant Enterococcus (VRE), Methicillin-resistant Staphylococcus aureus (MRSA) and carbapenem-resistant Enterobacteriaceae (CRE). This scenario is further complicated by the slow progress in achieving scientific breakthroughs in uncovering novel antibiotics following the 1960s. Most of the pharmaceutical industries have long diverted research funds away from the field of antibiotic discovery to more lucrative areas of drug development. If this situation is allowed to continue, humans will return to the pre-antibiotics era and potentially succumb to huge health and economic consequences. Fortunately, studies investigating various alternatives to antibiotics use in livestock show promising results. These alternatives include the application of bacteriophages and phage derived peptidoglycan degrading enzymes, engineered peptides, egg yolk antibodies, probiotics, prebiotics and synbiotics, as well as quorum quenching molecules. Therefore, this review aims to discuss the use of growth-promoting antibiotics and their impact on livestock and provide insights on the alternative approaches for animal husbandry.

Potential virus-mediated nitrogen cycling in oxygen-depleted oceanic waters

Viruses play an important role in the ecology and biogeochemistry of marine ecosystems. Beyond mortality and gene transfer, viruses can reprogram microbial metabolism during infection by expressing auxiliary metabolic genes (AMGs) involved in photosynthesis, central carbon metabolism, and nutrient cycling. While previous studies have focused on AMG diversity in the sunlit and dark ocean, less is known about the role of viruses in shaping metabolic networks along redox gradients associated with marine oxygen minimum zones (OMZs). Here, we analyzed relatively quantitative viral metagenomic datasets that profiled the oxygen gradient across Eastern Tropical South Pacific (ETSP) OMZ waters, assessing whether OMZ viruses might impact nitrogen (N) cycling via AMGs. Identified viral genomes encoded six N-cycle AMGs associated with denitrification, nitrification, assimilatory nitrate reduction, and nitrite transport. The majority of these AMGs (80%) were identified in T4-like Myoviridae phages, predicted to infect Cyanobacteria and Proteobacteria, or in unclassified archaeal viruses predicted to infect Thaumarchaeota. Four AMGs were exclusive to anoxic waters and had distributions that paralleled homologous microbial genes. Together, these findings suggest viruses modulate N-cycling processes within the ETSP OMZ and may contribute to nitrogen loss throughout the global oceans thus providing a baseline for their inclusion in the ecosystem and geochemical models.

The relationship between the phageome and human health: are bacteriophages beneficial or harmful microbes?

In the context of the global antibiotic resistance crisis, bacteriophages are increasingly becoming promising antimicrobial agents against multi-resistant bacteria. Indeed, a huge effort is being made to bring phage-derived products to the market, a process that will also require revising the current regulations in order to facilitate their approval. However, despite the evidence supporting the safety of phages for humans, the general public would still be reluctant to use 'viruses' for therapeutic purposes. In this scenario, we consider that it is important to discuss the role of these microorganisms in the equilibrium of the microbiota and how this relates to human health. To do that, this review starts by examining the role of phages as key players in bacterial communities (including those that naturally inhabit the human body), modulating the species composition and contributing to maintain a 'healthy' status quo. Additionally, in specific situations, e.g. an infectious disease, bacteriophages can be used as target-specific antimicrobials against pathogenic bacteria (phage therapy), while being harmless to the desirable microbiota. Apart from that, incipient research shows the potential application of these viruses to treat diseases caused by bacterial dysbiosis. This latter application would be comparable to the use of probiotics or prebiotics, since bacteriophages can indirectly improve the growth of beneficial bacteria in the gastrointestinal tract by removing undesirable competitors. On the other hand, possible adverse effects do not appear to be an impediment to promote phage therapy. Nonetheless, it is important to remember their potentially negative impact, mainly concerning their immunogenicity or their potential spread of virulence and antibiotic resistance genes, especially by temperate phages. Overall, we believe that phages should be largely considered beneficial microbes, although it is paramount not to overlook their potential risks.

Hybrid assembly of an agricultural slurry virome reveals a diverse and stable community with the potential to alter the metabolism and virulence of veterinary pathogens

BACKGROUND

Viruses are the most abundant biological entities on Earth, known to be crucial components of microbial ecosystems. However, there is little information on the viral community within agricultural waste. There are currently ~ 2.7 million dairy cattle in the UK producing 7-8% of their own bodyweight in manure daily, and 28 million tonnes annually. To avoid pollution of UK freshwaters, manure must be stored and spread in accordance with guidelines set by DEFRA. Manures are used as fertiliser, and widely spread over crop fields, yet little is known about their microbial composition. We analysed the virome of agricultural slurry over a 5-month period using short and long-read sequencing.

RESULTS

Hybrid sequencing uncovered more high-quality viral genomes than long or short-reads alone; yielding 7682 vOTUs, 174 of which were complete viral genomes. The slurry virome was highly diverse and dominated by lytic bacteriophage, the majority of which represent novel genera (~ 98%). Despite constant influx and efflux of slurry, the composition and diversity of the slurry virome was extremely stable over time, with 55% of vOTUs detected in all samples over a 5-month period. Functional annotation revealed a diverse and abundant range of auxiliary metabolic genes and novel features present in the community, including the agriculturally relevant virulence factor VapE, which was widely distributed across different phage genera that were predicted to infect several hosts. Furthermore, we identified an abundance of phage-encoded diversity-generating retroelements, which were previously thought to be rare on lytic viral genomes. Additionally, we identified a group of crAssphages, including lineages that were previously thought only to be found in the human gut.

CONCLUSIONS

The cattle slurry virome is complex, diverse and dominated by novel genera, many of which are not recovered using long or short-reads alone. Phages were found to encode a wide range of AMGs that are not constrained to particular groups or predicted hosts, including virulence determinants and putative ARGs. The application of agricultural slurry to land may therefore be a driver of bacterial virulence and antimicrobial resistance in the environment. Video abstract.

The Age of Phage: Friend or Foe in the New Dawn of Therapeutic and Biocontrol Applications?

Extended overuse and misuse of antibiotics and other antibacterial agents has resulted in an antimicrobial resistance crisis. Bacteriophages, viruses that infect bacteria, have emerged as a legitimate alternative antibacterial agent with a wide scope of applications which continue to be discovered and refined. However, the potential of some bacteriophages to aid in the acquisition, maintenance, and dissemination of negatively associated bacterial genes, including resistance and virulence genes, through transduction is of concern and requires deeper understanding in order to be properly addressed. In particular, their ability to interact with mobile genetic elements such as plasmids, genomic islands, and integrative conjugative elements (ICEs) enables bacteriophages to contribute greatly to bacterial evolution. Nonetheless, bacteriophages have the potential to be used as therapeutic and biocontrol agents within medical, agricultural, and food processing settings, against bacteria in both planktonic and biofilm environments. Additionally, bacteriophages have been deployed in developing rapid, sensitive, and specific biosensors for various bacterial targets. Intriguingly, their bioengineering capabilities show great promise in improving their adaptability and effectiveness as biocontrol and detection tools. This review aims to provide a balanced perspective on bacteriophages by outlining advantages, challenges, and future steps needed in order to boost their therapeutic and biocontrol potential, while also providing insight on their potential role in contributing to bacterial evolution and survival.

Metaviromics coupled with phage-host identification to open the viral 'black box'

Viruses are found in almost all biomes on Earth, with bacteriophages (phages) accounting for the majority of viral particles in most ecosystems. Phages have been isolated from natural environments using the plaque assay and liquid medium-based dilution culturing. However, phage cultivation is restricted by the current limitations in the number of culturable bacterial strains. Unlike prokaryotes, which possess universally conserved 16S rRNA genes, phages lack universal marker genes for viral taxonomy, thus restricting cultureindependent analyses of viral diversity. To circumvent these limitations, shotgun viral metagenome sequencing (i.e., metaviromics) has been developed to enable the extensive sequencing of a variety of viral particles present in the environment and is now widely used. Using metaviromics, numerous studies on viral communities have been conducted in oceans, lakes, rivers, and soils, resulting in many novel phage sequences. Furthermore, auxiliary metabolic genes such as ammonic monooxygenase C and β-lactamase have been discovered in viral contigs assembled from viral metagenomes. Current attempts to identify putative bacterial hosts of viral metagenome sequences based on sequence homology have been limited due to viral sequence variations. Therefore, culture-independent approaches have been developed to predict bacterial hosts using single-cell genomics and fluorescentlabeling. This review focuses on recent viral metagenome studies conducted in natural environments, especially in aquatic ecosystems, and their contributions to phage ecology. Here, we concluded that although metaviromics is a key tool for the study of viral ecology, this approach must be supplemented with phage-host identification, which in turn requires the cultivation of phage-bacteria systems.

Antimicrobial Resistance and Bacteriophages: An Overlooked Intersection in Water Disinfection

This article focuses on how bacteriophages (phages), antibiotic-resistance genes (ARGs), and disinfection practices intersect. Phages are considered to be the most abundant biological entities on Earth and they have the potential to transfer genes (including ARGs) among their bacterial hosts. In the urban water cycle, phages are used as indicators of fecal pollution and surrogates for human viral pathogens but they are also known to withstand common disinfection treatments deployed to produce safe drinking/reclaimed water. Recent studies also suggest that phages have the potential to become an additional footprint to monitor water safety. A precautionary approach should therefore include phages in surveillance programs aimed at monitoring antimicrobial resistance (AMR) in the urban water cycle. This article argues that phages ought to be used to assess the efficiency of disinfection treatments (both classical and novel) on reducing the risk associated with antibiotic resistance. Finally, this article discusses contributions to the advancement of AMR stewardship in aquatic settings and is relevant for researchers and water industry practitioners.

Metagenomics analysis of bacteriophages and antimicrobial resistance from global urban sewage

Bacteriophages, or phages, are ubiquitous bacterial and archaeal viruses with an estimated total global population of 10³¹. It is well-known that wherever there are bacteria, their phage counterparts will be found, aiding in shaping the bacterial population. The present study used metagenomic data from global influent sewage in 79 cities in 60 countries to identify phages associated with bacteria and to explore their potential role in antimicrobial resistance gene (ARG) dissemination. The reads were mapped to known databases for bacteriophages and their abundances determined and correlated to geographic origin and the countries socio-economic status, as well as the abundances of bacterial species and ARG. We found that some phages were not equally distributed on a global scale, but their distribution was rather dictated by region and the socioeconomic status of the specific countries. This study provides a preliminary insight into the global and regional distribution of phages and their potential impact on the transmission of ARGs between bacteria. Moreover, the findings may indicate that phages in sewage could have adopted a lytic lifestyle, meaning that most may not be associated with bacteria and instead may be widely distributed as free-living phages, which are known to persist longer in the environment than their hosts. In addition, a significant correlation between phages and ARGs was obtained, indicating that phages may play a role in ARG dissemination. However, further analyses are needed to establish the true relationship between phages and ARGs due to a low abundance of the phages identified.

Fitness benefits to bacteria of carrying prophages and prophage-encoded antibiotic-resistance genes peak in different environments

Understanding the role of horizontal gene transfer (HGT) in adaptation is a key challenge in evolutionary biology. In microbes, an important mechanism of HGT is prophage acquisition (phage genomes integrated into bacterial chromosomes). Prophages can influence bacterial fitness via the transfer of beneficial genes (including antibiotic‐resistance genes, ARGs), protection from superinfecting phages, or switching to a lytic lifecycle that releases free phages infectious to competitors. We expect these effects to depend on environmental conditions because of, for example, environment‐dependent induction of the lytic lifecycle. However, it remains unclear how costs/benefits of prophages vary across environments. Here, studying prophages with/without ARGs in Escherichia coli, we disentangled the effects of prophages alone and adaptive genes they carry. In competition with prophage‐free strains, benefits from prophages and ARGs peaked in different environments. Prophages were most beneficial when induction of the lytic lifecycle was common, whereas ARGs were more beneficial upon antibiotic exposure and with reduced prophage induction. Acquisition of prophage‐encoded ARGs by competing strains was most common when prophage induction, and therefore free phages, were common. Thus, selection on prophages and adaptive genes they carry varies independently across environments, which is important for predicting the spread of mobile/integrating genetic elements and their role in evolution.

Long-read metagenomics using PromethION uncovers oral bacteriophages and their interaction with host bacteria

Bacteriophages (phages), or bacterial viruses, are very diverse and highly abundant worldwide, including as a part of the human microbiomes. Although a few metagenomic studies have focused on oral phages, they relied on short-read sequencing. Here, we conduct a long-read metagenomic study of human saliva using PromethION. Our analyses, which integrate both PromethION and HiSeq data of >30 Gb per sample with low human DNA contamination, identify hundreds of viral contigs; 0-43.8% and 12.5-56.3% of the confidently predicted phages and prophages, respectively, do not cluster with those reported previously. Our analyses demonstrate enhanced scaffolding, and the ability to place a prophage in its host genomic context and enable its taxonomic classification. Our analyses also identify a Streptococcus phage/prophage group and nine jumbo phages/prophages. 86% of the phage/prophage group and 67% of the jumbo phages/prophages contain remote homologs of antimicrobial resistance genes. Pan-genome analysis of the phages/prophages reveals remarkable diversity, identifying 0.3% and 86.4% of the genes as core and singletons, respectively. Furthermore, our study suggests that oral phages present in human saliva are under selective pressure to escape CRISPR immunity. Our study demonstrates the power of long-read metagenomics utilizing PromethION in uncovering bacteriophages and their interaction with host bacteria.

Metagenomic compendium of 189,680 DNA viruses from the human gut microbiome

Bacteriophages have important roles in the ecology of the human gut microbiome but are under-represented in reference databases. To address this problem, we assembled the Metagenomic Gut Virus catalogue that comprises 189,680 viral genomes from 11,810 publicly available human stool metagenomes. Over 75% of genomes represent double-stranded DNA phages that infect members of the Bacteroidia and Clostridia classes. Based on sequence clustering we identified 54,118 candidate viral species, 92% of which were not found in existing databases. The Metagenomic Gut Virus catalogue improves detection of viruses in stool metagenomes and accounts for nearly 40% of CRISPR spacers found in human gut Bacteria and Archaea. We also produced a catalogue of 459,375 viral protein clusters to explore the functional potential of the gut virome. This revealed tens of thousands of diversity-generating retroelements, which use error-prone reverse transcription to mutate target genes and may be involved in the molecular arms race between phages and their bacterial hosts.

A generalised model for generalised transduction: the importance of co-evolution and stochasticity in phage mediated antimicrobial resistance transfer

Antimicrobial resistance is a major global challenge. Of particular concern are mobilizable elements that can transfer resistance genes between bacteria, leading to pathogens with new combinations of resistance. To date, mathematical models have largely focussed on transfer of resistance by plasmids, with fewer studies on transfer by bacteriophages. We aim to understand how best to model transfer of resistance by transduction by lytic phages. We show that models of lytic bacteriophage infection with empirically derived realistic phage parameters lead to low numbers of bacteria, which, in low population or localised environments, lead to extinction of bacteria and phage. Models that include antagonistic co-evolution of phage and bacteria produce more realistic results. Furthermore, because of these low numbers, stochastic dynamics are shown to be important, especially to spread of resistance. When resistance is introduced, resistance can sometimes be fixed, and at other times die out, with the probability of each outcome sensitive to bacterial and phage parameters. Specifically, that outcome most strongly depends on the baseline death rate of bacteria, with phage-mediated spread favoured in benign environments with low mortality over more hostile environments. We conclude that larger-scale models should consider spatial compartmentalisation and heterogeneous microenviroments, while encompassing stochasticity and co-evolution.

The Russian Doll Model: How Bacteria Shape Successful and Sustainable Inter-Kingdom Relationships

Successful inter-kingdom relationships are based upon a dynamic balance between defense and cooperation. A certain degree of competition is necessary to guarantee life spread and development. On the other hand, cooperation is a powerful tool to ensure a long lasting adaptation to changing environmental conditions and to support evolution to a higher level of complexity. Bacteria can interact with their (true or potential) parasites (i.e., phages) and with their multicellular hosts. In these model interactions, bacteria learnt how to cope with their inner and outer host, transforming dangerous signals into opportunities and modulating responses in order to achieve an agreement that is beneficial for the overall participants, thus giving rise to a more complex "organism" or ecosystem. In this review, particular attention will be addressed to underline the minimal energy expenditure required for these successful interactions [e.g., moonlighting proteins, post-translational modifications (PTMs), and multitasking signals] and the systemic vision of these processes and ways of life in which the system proves to be more than the sum of the single components. Using an inside-out perspective, I will examine the possibility of multilevel interactions, in which viruses help bacteria to cope with the animal host and bacteria support the human immune system to counteract viral infection in a circular vision. In this sophisticated network, bacteria represent the precious link that insures system stability with relative low energy expenditure.

Transductomics: sequencing-based detection and analysis of transduced DNA in pure cultures and microbial communities

BACKGROUND

Horizontal gene transfer (HGT) plays a central role in microbial evolution. Our understanding of the mechanisms, frequency, and taxonomic range of HGT in polymicrobial environments is limited, as we currently rely on historical HGT events inferred from genome sequencing and studies involving cultured microorganisms. We lack approaches to observe ongoing HGT in microbial communities.

RESULTS

To address this knowledge gap, we developed a DNA sequencing-based "transductomics" approach that detects and characterizes microbial DNA transferred via transduction. We validated our approach using model systems representing a range of transduction modes and show that we can detect numerous classes of transducing DNA. Additionally, we show that we can use this methodology to obtain insights into DNA transduction among all major taxonomic groups of the intestinal microbiome.

CONCLUSIONS

The transductomics approach that we present here allows for the detection and characterization of genes that are potentially transferred between microbes in complex microbial communities at the time of measurement and thus provides insights into real-time ongoing horizontal gene transfer. This work extends the genomic toolkit for the broader study of mobile DNA within microbial communities and could be used to understand how phenotypes spread within microbiomes. Video Abstract.

Antimicrobial resistance in enteric bacteria: current state and next-generation solutions

Antimicrobial resistance is one of the largest threats to global health and imposes substantial burdens in terms of morbidity, mortality, and economic costs. The gut is a key conduit for the genesis and spread of antimicrobial resistance in enteric bacterial pathogens. Distinct bacterial species that cause enteric disease can exist as invasive enteropathogens that immediately evoke gastrointestinal distress, or pathobionts that can arise from established bacterial commensals to inflict dysbiosis and disease. Furthermore, various environmental reservoirs and stressors facilitate the evolution and transmission of resistance. In this review, we present a comprehensive discussion on circulating resistance profiles and gene mobilization strategies of the most problematic species of enteric bacterial pathogens. Importantly, we present emerging approaches toward surveillance of pathogens and their resistance elements as well as promising treatment strategies that can circumvent common resistance mechanisms.

Exploration into the origins and mobilization of di-hydrofolate reductase genes and the emergence of clinical resistance to trimethoprim

Trimethoprim is a synthetic antibacterial agent that targets folate biosynthesis by competitively binding to the di-hydrofolate reductase enzyme (DHFR). Trimethoprim is often administered synergistically with sulfonamide, another chemotherapeutic agent targeting the di-hydropteroate synthase (DHPS) enzyme in the same pathway. Clinical resistance to both drugs is widespread and mediated by enzyme variants capable of performing their biological function without binding to these drugs. These mutant enzymes were assumed to have arisen after the discovery of these synthetic drugs, but recent work has shown that genes conferring resistance to sulfonamide were present in the bacterial pangenome millions of years ago. Here, we apply phylogenetics and comparative genomics methods to study the largest family of mobile trimethoprim-resistance genes (dfrA). We show that most of the dfrA genes identified to date map to two large clades that likely arose from independent mobilization events. In contrast to sulfonamide resistance (sul) genes, we find evidence of recurrent mobilization in dfrA genes. Phylogenetic evidence allows us to identify novel dfrA genes in the emerging pathogen Acinetobacter baumannii, and we confirm their resistance phenotype in vitro. We also identify a cluster of dfrA homologues in cryptic plasmid and phage genomes, but we show that these enzymes do not confer resistance to trimethoprim. Our methods also allow us to pinpoint the chromosomal origin of previously reported dfrA genes, and we show that many of these ancient chromosomal genes also confer resistance to trimethoprim. Our work reveals that trimethoprim resistance predated the clinical use of this chemotherapeutic agent, but that novel mutations have likely also arisen and become mobilized following its widespread use within and outside the clinic. Hence, this work confirms that resistance to novel drugs may already be present in the bacterial pangenome, and stresses the importance of rapid mobilization as a fundamental element in the emergence and global spread of resistance determinants.

DRAM for distilling microbial metabolism to automate the curation of microbiome function

Microbial and viral communities transform the chemistry of Earth's ecosystems, yet the specific reactions catalyzed by these biological engines are hard to decode due to the absence of a scalable, metabolically resolved, annotation software. Here, we present DRAM (Distilled and Refined Annotation of Metabolism), a framework to translate the deluge of microbiome-based genomic information into a catalog of microbial traits. To demonstrate the applicability of DRAM across metabolically diverse genomes, we evaluated DRAM performance on a defined, in silico soil community and previously published human gut metagenomes. We show that DRAM accurately assigned microbial contributions to geochemical cycles and automated the partitioning of gut microbial carbohydrate metabolism at substrate levels. DRAM-v, the viral mode of DRAM, established rules to identify virally-encoded auxiliary metabolic genes (AMGs), resulting in the metabolic categorization of thousands of putative AMGs from soils and guts. Together DRAM and DRAM-v provide critical metabolic profiling capabilities that decipher mechanisms underpinning microbiome function.

Seasonal dynamics in taxonomy and function within bacterial and viral metagenomic assemblages recovered from a freshwater agricultural pond

BACKGROUND

Ponds are important freshwater habitats that support both human and environmental activities. However, relative to their larger counterparts (e.g. rivers, lakes), ponds are understudied, especially with regard to their microbial communities. Our study aimed to fill this knowledge gap by using culture-independent, high-throughput sequencing to assess the dynamics, taxonomy, and functionality of bacterial and viral communities in a freshwater agricultural pond.

RESULTS

Water samples (n = 14) were collected from a Mid-Atlantic agricultural pond between June 2017 and May 2018 and filtered sequentially through 1 and 0.2 μm filter membranes. Total DNA was then extracted from each filter, pooled, and subjected to 16S rRNA gene and shotgun sequencing on the Illumina HiSeq 2500 platform. Additionally, on eight occasions water filtrates were processed for viral metagenomes (viromes) using chemical concentration and then shotgun sequenced. A ubiquitous freshwater phylum, Proteobacteria was abundant at all sampling dates throughout the year. However, environmental characteristics appeared to drive the structure of the community. For instance, the abundance of Cyanobacteria (e.g. Nostoc) increased with rising water temperatures, while a storm event appeared to trigger an increase in overall bacterial diversity, as well as the relative abundance of Bacteroidetes. This event was also associated with an increase in the number of antibiotic resistance genes. The viral fractions were dominated by dsDNA of the order Caudovirales, namely Siphoviridae and Myovirdae.

CONCLUSIONS

Overall, this study provides one of the largest datasets on pond water microbial ecology to date, revealing seasonal trends in the microbial taxonomic composition and functional potential.

A converging subset of soil bacterial taxa is permissive to the IncP-1 plasmid pKJK5 across a range of soil copper contamination

Stressors like metals or antibiotics can affect bacterial community permissiveness for plasmid uptake, but there is little knowledge about long-term effects of such stressors on the evolution of community permissiveness. We assessed the effect of more than 90 years of soil Cu contamination on bacterial community permissiveness (i.e. uptake ability) toward a gfp-tagged IncP-1 plasmid (pKJK5) introduced via an Escherichia coli donor. Plasmid transfer events from the donor to the recipient soil bacterial community were quantified and transconjugants were subsequently isolated by fluorescence activated cell sorting and identified by 16S rRNA gene amplicon sequencing. Transfer frequency of plasmid pKJK5 was reduced in bacterial communities extracted from highly Cu contaminated (4526 mg kg-1) soil compared to corresponding communities extracted from moderately (458 mg kg-1) Cu contaminated soil and a low Cu reference soil (15 mg kg-1). The taxonomic composition of the transconjugal pools showed remarkable similarities irrespective of the degree of soil Cu contamination and despite contrasting compositions of the extracted recipient communities and the original soil communities. Permissiveness assessed at the level of individual operational taxonomic units (OTUs; 16S rRNA gene 97% sequence similarity threshold) was only slightly affected by soil Cu level and high replicate variability of OTU-level permissiveness indicated a role of stochastic events in IncP-1 plasmid transfer or strain-to-strain permissiveness variability.

Tackling Multidrug Resistance in Streptococci - From Novel Biotherapeutic Strategies to Nanomedicines

The pyogenic streptococci group includes pathogenic species for humans and other animals and has been associated with enduring morbidity and high mortality. The main reason for the treatment failure of streptococcal infections is the increased resistance to antibiotics. In recent years, infectious diseases caused by pyogenic streptococci resistant to multiple antibiotics have been raising with a significant impact to public health and veterinary industry. The rise of antibiotic-resistant streptococci has been associated to diverse mechanisms, such as efflux pumps and modifications of the antimicrobial target. Among streptococci, antibiotic resistance emerges from previously sensitive populations as result of horizontal gene transfer or chromosomal point mutations due to excessive use of antimicrobials. Streptococci strains are also recognized as biofilm producers. The increased resistance of biofilms to antibiotics among streptococci promote persistent infection, which comprise circa 80% of microbial infections in humans. Therefore, to overcome drug resistance, new strategies, including new antibacterial and antibiofilm agents, have been studied. Interestingly, the use of systems based on nanoparticles have been applied to tackle infection and reduce the emergence of drug resistance. Herein, we present a synopsis of mechanisms associated to drug resistance in (pyogenic) streptococci and discuss some innovative strategies as alternative to conventional antibiotics, such as bacteriocins, bacteriophage, and phage lysins, and metal nanoparticles. We shall provide focused discussion on the advantages and limitations of agents considering application, efficacy and safety in the context of impact to the host and evolution of bacterial resistance.

Metagenomic Insights into the Sewage RNA Virosphere of a Large City

Sewage-associated viruses can cause several human and animal diseases, such as gastroenteritis, hepatitis, and respiratory infections. Therefore, their detection in wastewater can reflect current infections within the source population. To date, no viral study has been performed using the sewage of any large South American city. In this study, we used viral metagenomics to obtain a single sample snapshot of the RNA virosphere in the wastewater from Santiago de Chile, the seventh largest city in the Americas. Despite the overrepresentation of dsRNA viruses, our results show that Santiago’s sewage RNA virosphere was composed mostly of unknown sequences (88%), while known viral sequences were dominated by viruses that infect bacteria (60%), invertebrates (37%) and humans (2.4%). Interestingly, we discovered three novel genogroups within the Picobirnaviridae family that can fill major gaps in this taxa’s evolutionary history. We also demonstrated the dominance of emerging Rotavirus genotypes, such as G8 and G6, that have displaced other classical genotypes, which is consistent with recent clinical reports. This study supports the usefulness of sewage viral metagenomics for public health surveillance. Moreover, it demonstrates the need to monitor the viral component during the wastewater treatment and recycling process, where this virome can constitute a reservoir of human pathogens.

Shining Light on Human Gut Bacteriophages

The human gut is a complex environment that contains a multitude of microorganisms that are collectively termed the microbiome. Multiple factors have a role to play in driving the composition of human gut bacterial communities either toward homeostasis or the instability that is associated with many disease states. One of the most important forces are likely to be bacteriophages, bacteria-infecting viruses that constitute by far the largest portion of the human gut virome. Despite this, bacteriophages (phages) are the one of the least studied residents of the gut. This is largely due to the challenges associated with studying these difficult to culture entities. Modern high throughput sequencing technologies have played an important role in improving our understanding of the human gut phageome but much of the generated sequencing data remains uncharacterised. Overcoming this requires database-independent bioinformatic pipelines and even those phages that are successfully characterized only provide limited insight into their associated biological properties, and thus most viral sequences have been characterized as “viral dark matter.” Fundamental to understanding the role of phages in shaping the human gut microbiome, and in turn perhaps influencing human health, is how they interact with their bacterial hosts. An essential aspect is the isolation of novel phage-bacteria host pairs by direct isolation through various screening methods, which can transform in silico phages into a biological reality. However, this is also beset with multiple challenges including culturing difficulties and the use of traditional methods, such as plaquing, which may bias which phage-host pairs that can be successfully isolated. Phage-bacteria interactions may be influenced by many aspects of complex human gut biology which can be difficult to reproduce under laboratory conditions. Here we discuss some of the main findings associated with the human gut phageome to date including composition, our understanding of phage-host interactions, particularly the observed persistence of virulent phages and their hosts, as well as factors that may influence these highly intricate relationships. We also discuss current methodologies and bottlenecks hindering progression in this field and identify potential steps that may be useful in overcoming these hurdles.

Dynamics of bacteriophages in gut of giant pandas reveal a potential regulation of dietary intake on bacteriophage composition

Fecal samples of cubs and adults of giant pandas were examined to determine the effects of diets on the diversity and dynamics of gut bacteriophages. Enterobacteria phage, Salmonella phage, Escherichia phage, Shigella phage, Klebsiella phage, and Lactococcus phage were found to be dominant in both cub and adult samples. Citrobacter phage, Cronobacter phage, Pectobacterium phage, Erwinia phage, Dickeya phage, Erwinia phage, Enterococcus phage, and Pseudomonas phage were more abundant in adults, while Lactococcus phage, Streptococcus phage, Lactobacillus phage, and Leuconostoc phage were more abundant in cubs. The abundance and diversity of the majority of phage species were increased in pandas with age. There was an increase in the abundance of Pectobacterium phage and a decrease in the abundance of Lactobacillus phage, Leuconostoc phage, Bacillus phage, and Streptococcus phage in adults. As cubs and adults of giant pandas have different dietary habits, these observations suggest a significant effect of diets on the composition and abundance of gut bacteriophages in giant pandas.

Tracking resistomes, virulence genes, and bacterial pathogens in long-term manure-amended greenhouse soils

Organic manure has been implicated as an important source of antibiotic resistance genes (ARGs) in agricultural soils. However, the profiles of biocide resistance genes (BRGs), metal resistance genes (MRGs) and virulence genes (VGs) and their bacterial hosts in manure-amended soils remain largely unknown. Herein, a systematic metagenome-based survey was conducted to comprehensively explore the changes in resistomes, VGs and their bacterial hosts, mobile genetic elements (MGEs), and pathogenic bacteria in manure-amended greenhouse soils. Many manure-borne ARGs, BRGs, MRGs, VGs, and bacterial pathogens could be transferred into soils by applying manures, and their abundance and diversity were markedly positively correlated with greenhouse planting years (manure amendment years). The main ARGs transferred from manures to soils conferred resistance to tetracycline, aminoglycoside, and macrolide-lincosamide-streptogramin. Both statistical analysis and gene arrangements showed a good positive co-occurrence pattern of ARGs/BRGs/MRGs/VGs and MGEs. Furthermore, bacterial hosts of resistomes and VGs were significantly changed in the greenhouse soils in comparison with the field soils. Our findings confirmed the migration and dissemination of resistomes, VGs, and bacterial pathogens, and their accumulation and persistence were correlated with the continuous application of manures.

Standardized bacteriophage purification for personalized phage therapy

The world is on the cusp of a post-antibiotic era, but researchers and medical doctors have found a way forward-by looking back at how infections were treated before the advent of antibiotics, namely using phage therapy. Although bacteriophages (phages) continue to lack drug approval in Western medicine, an increasing number of patients are being treated on an expanded-access emergency investigational new drug basis. To streamline the production of high-quality and clinically safe phage preparations, we developed a systematic procedure for medicinal phage isolation, liter-scale cultivation, concentration and purification. The 16- to 21-day procedure described in this protocol uses a combination of modified classic techniques, modern membrane filtration processes and no organic solvents to yield on average 23 mL of 10¹¹ plaque-forming units (PFUs) per milliliter for Pseudomonas, Klebsiella, and Serratia phages tested. Thus, a single production run can produce up to 64,000 treatment doses at 10⁹ PFUs, which would be sufficient for most expanded-access phage therapy cases and potentially for clinical phase I/II applications. The protocol focuses on removing endotoxins early by conducting multiple low-speed centrifugations, microfiltration, and cross-flow ultrafiltration, which reduced endotoxins by up to 10⁶-fold in phage preparations. Implementation of a standardized phage cultivation and purification across research laboratories participating in phage production for expanded-access phage therapy might be pivotal to reintroduce phage therapy to Western medicine.

Identification of Antimicrobial Resistance Determinants in Aeromonas veronii Strain MS-17-88 Recovered From Channel Catfish (Ictalurus punctatus)

Aeromonas veronii is a Gram-negative species ubiquitous in different aquatic environments and capable of causing a variety of diseases to a broad host range. Aeromonas species have the capability to carry and acquire antimicrobial resistance (AMR) elements, and currently multi-drug resistant (MDR) Aeromonas isolates are commonly found across the world. A. veronii strain MS-17-88 is a MDR strain isolated from catfish in the southeastern United States. The present study was undertaken to uncover the mechanism of resistance in MDR A. veronii strain MS-17-88 through the detection of genomic features. To achieve this, genomic DNA was extracted, sequenced, and assembled. The A. veronii strain MS-17-88 genome comprised 5,178,226-bp with 58.6% G+C, and it encoded several AMR elements, including imiS, ampS, mcr-7.1, mcr-3, catB2, catB7, catB1, floR, vat(F), tet(34), tet(35), tet(E), dfrA3, and tetR. The phylogeny and resistance profile of a large collection of A. veronii strains, including MS-17-88, were evaluated. Phylogenetic analysis showed a close relationship between MS-17-88 and strain Ae5 isolated from fish in China and ARB3 strain isolated from pond water in Japan, indicating a common ancestor of these strains. Analysis of phage elements revealed 58 intact, 63 incomplete, and 15 questionable phage elements among the 53 A. veronii genomes. The average phage element number is 2.56 per genome, and strain MS-17-88 is one of two strains having the maximum number of identified prophage elements (6 elements each). The profile of resistance against various antibiotics across the 53 A. veronii genomes revealed the presence of tet(34), mcr-7.1, mcr-3, and dfrA3 in all genomes (100%). By comparison, sul1 and sul2 were detected in 7.5% and 1.8% of A. veronii genomes. Nearly 77% of strains carried tet(E), and 7.5% of strains carried floR. This result suggested a low abundance and prevalence of sulfonamide and florfenicol resistance genes compared with tetracycline resistance among A. veronii strains. Overall, the present study provides insights into the resistance patterns among 53 A. veronii genomes, which can inform therapeutic options for fish affected by A. veronii.

Isolation and Characterization of Bacteriophages That Infect Citrobacter rodentium, a Model Pathogen for Intestinal Diseases

Enteropathogenic Escherichia coli (EPEC) is a major pathogen for diarrheal diseases among children. Antibiotics, when used appropriately, are effective; however, their overuse and misuse have led to the rise of antibiotic resistance worldwide. Thus, there are renewed efforts into the development of phage therapy as an alternative antibacterial therapy. Because EPEC in vivo models have shortcomings, a surrogate is used to study the mouse pathogen Citrobacter rodentium in animal models. In this study, two new phages CrRp3 and CrRp10, which infect C. rodentium, were isolated and characterized. CrRp3 was found to be a new species within the genus Vectrevirus, and CrRp10 is a new strain within the species Escherichia virus Ime09, in the genus Tequatrovirus. Both phages appear to have independently evolved from E. coli phages, rather than other Citrobacter spp. phages. Neither phage strain carries known genes associated with bacterial virulence, antibiotic resistance, or lysogeny. CrRp3 is more potent, having a 24-fold faster adsorption rate and shorter lytic cycle when compared to the same properties of CrRp10. However, a lysis curve analysis revealed that CrRp10 prevented growth of C. rodentium for 18 h, whereas resistance developed against CrRp3 within 9 h. We also show that hypoxic (5% oxygen) conditions decreased CrRp3 ability to control bacterial densities in culture. In contrast, low oxygen conditions did not affect CrRp10 ability to replicate on C. rodentium. Together, CrRp10 is likely to be the better candidate for future phage therapy investigations.

Growing Trend of Fighting Infections in Aquaculture Environment-Opportunities and Challenges of Phage Therapy

Phage therapy, a promising alternative to antimicrobial treatment of bacterial diseases, is getting more and more popular, especially due to the rising awareness of antibiotic resistance and restrictions in antibiotics' use. During recent years, we observed a growing trend of bacteriophages' application in aquaculture, which in each year reports high losses due to bacterial diseases. This review provides an update of the status of bacteriophage therapy for the treatment and prevention of infections in the aquatic environment. As it is still mostly in the scientific stage, there are a few constraints that may prevent effective therapy. Therefore, specific characteristics of bacteriophages, that can act in favor or against their successful use in treatment, were described. We underlined aspects that need to be considered: specificity of phages, bacterial resistance, safety, immune response of the host organism, formulation, administration and stability of phage preparations as well as bacteriophages' influence on the environment. The biggest challenge to overcome is finding the right balance between the desired and problematic characteristics of bacteriophages. Finally, regulatory approval challenges may be encountered by bacteriophage manufacturers. Even though there are still some technical constraints connected with the global use of bacteriophage therapy, it was concluded that it can be successfully applied in aquaculture.

Freshwater viral metagenome reveals novel and functional phage-borne antibiotic resistance genes

BACKGROUND

Antibiotic resistance developed by bacteria is a significant threat to global health. Antibiotic resistance genes (ARGs) spread across different bacterial populations through multiple dissemination routes, including horizontal gene transfer mediated by bacteriophages. ARGs carried by bacteriophages are considered especially threatening due to their prolonged persistence in the environment, fast replication rates, and ability to infect diverse bacterial hosts. Several studies employing qPCR and viral metagenomics have shown that viral fraction and viral sequence reads in clinical and environmental samples carry many ARGs. However, only a few ARGs have been found in viral contigs assembled from metagenome reads, with most of these genes lacking effective antibiotic resistance phenotypes. Owing to the wide application of viral metagenomics, nevertheless, different classes of ARGs are being continuously found in viral metagenomes acquired from diverse environments. As such, the presence and functionality of ARGs encoded by bacteriophages remain up for debate.

RESULTS

We evaluated ARGs excavated from viral contigs recovered from urban surface water viral metagenome data. In virome reads and contigs, diverse ARGs, including polymyxin resistance genes, multidrug efflux proteins, and β-lactamases, were identified. In particular, when a lenient threshold of e value of ≤ 1 × e-5 and query coverage of ≥ 60% were employed in the Resfams database, the novel β-lactamases blaHRV-1 and blaHRVM-1 were found. These genes had unique sequences, forming distinct clades of class A and subclass B3 β-lactamases, respectively. Minimum inhibitory concentration analyses for E. coli strains harboring blaHRV-1 and blaHRVM-1 and catalytic kinetics of purified HRV-1 and HRVM-1 showed reduced susceptibility to penicillin, narrow- and extended-spectrum cephalosporins, and carbapenems. These genes were also found in bacterial metagenomes, indicating that they were harbored by actively infecting phages.

CONCLUSION

Our results showed that viruses in the environment carry as-yet-unreported functional ARGs, albeit in small quantities. We thereby suggest that environmental bacteriophages could be reservoirs of widely variable, unknown ARGs that could be disseminated via virus-host interactions. Video abstract.

Probing the Mobilome: Discoveries in the Dynamic Microbiome

There has been an explosion of metagenomic data representing human, animal, and environmental microbiomes. This provides an unprecedented opportunity for comparative and longitudinal studies of many functional aspects of the microbiome that go beyond taxonomic classification, such as profiling genetic determinants of antimicrobial resistance, interactions with the host, potentially clinically relevant functions, and the role of mobile genetic elements (MGEs). One of the most important but least studied of these aspects are the MGEs, collectively referred to as the 'mobilome'. Here we elaborate on the benefits and limitations of using different metagenomic protocols, discuss the relative merits of various sequencing technologies, and highlight relevant bioinformatics tools and pipelines to predict the presence of MGEs and their microbial hosts.