Bacteriophages in the human gut: Our fellow travelers throughout life and potential biomarkers of heath or disease

Host specific adaptations of Ligilactobacillus aviarius to poultry

The genus Ligilactobacillus encompasses species adapted to vertebrate hosts and fermented food. Their genomes encode adaptations to the host lifestyle. Reports of gut microbiota from chicken and turkey gastrointestinal tract have shown a high persistence of Ligilactobacillus aviarius along the digestive system compared to other species found in the same host. However, its adaptations to poultry as a host has not yet been described. In this work, the pan-genome of Ligilactobacillus aviarius was explored to describe the functional adaptability to the gastrointestinal environment. The core genome is composed of 1179 gene clusters that are present at least in one copy that codifies to structural, ribosomal and biogenesis proteins. The rest of the identified regions were classified into three different functional clusters of orthologous groups (clusters) that codify carbohydrate metabolism, envelope biogenesis, viral defence mechanisms, and mobilome inclusions. The pan-genome of Ligilactobacillus aviarius is a closed pan-genome, frequently found in poultry and highly prevalent across chicken faecal samples. The genome of L. aviarius codifies different clusters of glycoside hydrolases and glycosyltransferases that mediate interactions with the host cells. Accessory features, such as antiviral mechanisms and prophage inclusions, variate amongst strains from different GIT sections. This information provides hints about the interaction of this species with viral particles and other bacterial species. This work highlights functional adaptability traits present in L. aviarius that make it a dominant key member of the poultry gut microbiota and enlightens the convergent ecological relation of this species to the poultry gut environment.

Obesity, cancer, and response to immune checkpoint inhibitors: Could the gut microbiota be the mechanistic link?

Immune checkpoint inhibitors (ICI) have deeply changed the therapeutic management of a broad spectrum of solid tumors. Recent observations showed that obese patients receiving ICIs might have better outcomes than those with normal weight, while obesity was historically associated with a worse prognosis in cancer patients. Of note, obesity is associated with alterations in the gut microbiome profile, which interacts with immune and inflammatory pathways, both at the systemic and intratumoral levels. As the influence of the gut microbiota on the response to ICI has been repeatedly reported, a specific gut microbiome profile in obese cancer patients may be involved in their better response to ICI. This review summarizes recent data on the interactions between obesity, gut microbiota, and ICIs. In addition, we highlight possible pathophysiological mechanisms supporting the hypothesis that gut microbiota could be one of the links between obesity and poor response to ICIs.

Bacteriophage-based techniques for elucidating the function of zebrafish gut microbiota

Bacteriophages (or phages) are unique viruses that can specifically infect bacteria. Since their discovery by Twort and d'Herelle, phages with bacterial specificity have played important roles in microbial regulation. The intestinal microbiota and host health are intimately linked with nutrient, metabolism, development, and immunity aspects. However, the mechanism of interactions between the composition of the microbiota and their functions in maintaining host health still needs to be further explored. To address the lack of methodology and functions of intestinal microbiota in the host, we first proposed that, with the regulations of special intestinal microbiota and applications of germ-free (GF) zebrafish model, phages would be used to infect and reduce/eliminate the defined gut bacteria in the conventionally raised (CR) zebrafish and compared with the GF zebrafish colonized with defined bacterial strains. Thus, this review highlighted the background and roles of phages and their functional characteristics, and we also summarized the phage-specific infection of target microorganisms, methods to improve the phage specificity, and their regulation within the zebrafish model and gut microbial functional study. Moreover, the primary protocol of phage therapy to control the intestinal microbiota in zebrafish models from larvae to adults was recommended including phage screening from natural sources, identification of host ranges, and experimental design in the animal. A well understanding of the interaction and mechanism between phages and gut bacteria in the host can potentially provide powerful strategies or techniques for preventing bacteria-related human diseases by precisely regulating in vitro and in vivo, which will provide novel insights for phages' application and combined research in the future. KEY POINTS: • Zebrafish models for clarifying the microbial and phages' functions were discussed • Phages infect host bacteria with exquisite specificity and efficacy • Phages can reduce/eliminate the defined gut bacteria to clarify their function.

Dynamics of nasopharyngeal tract phageome and association with disease severity and age of patients during three waves of COVID-19

In December 2019, several patients were hospitalized and diagnosed with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, which subsequently led to a global pandemic. To date, there are no studies evaluating the relationship between the respiratory phageome and the SARS-CoV-2 infection. The current study investigated the phageome profiles in the nasopharyngeal swabs collected from 55 patients during the three different waves of coronavirus disease 2019 (COVID-19) in the Campania Region (Southern Italy). Data obtained from the taxonomic profiling show that phage families belonging to the order Caudovirales have a high abundance in the patient samples. Moreover, the severity of the COVID-19 infection seems to be correlated with the phage abundance.

Systemic Evaluation of the Effect of Diabetes Mellitus on Breast Cancer in a Mouse Model

Breast cancer complicated with diabetes mellitus (DM) is a common disease. To evaluate the effect of preexisting DM on breast cancer progression without drug interference, we used a streptozotocin (STZ)-induced type 2 diabetes mellitus BALB/c mouse model. We found that 4T1 breast cancer complicated with DM decreased the mouse survival time compared with 4T1-bearing mice. The diversity of gut microbiome was affected by DM. The infiltration of mucosal-associated invariant T cell (MAIT), CD8+ T cell, and CD4+ T cell in the tumor was significantly decreased in the DM-4T1 group compared with the 4T1 group. The transcriptome data of tumor tissues indicated that the expressions of inflammatory C–C chemokine- and metabolism-related genes were greatly changed. The abnormal expression of these genes may be related with the decreased T-cell infiltration in DM-4T1. In conclusion, the gut microbiome and tumor microenvironment of diabetic breast cancer patients have unique features. The effect of diabetes on breast cancer should be considered in the treatment for diabetic breast cancer patients.

Comparative Genomic Analysis Reveals Intestinal Habitat Adaptation of Ligilactobacillus equi Rich in Prophage and Degrading Cellulase

Ligilactobacillus equi is common in the horse intestine, alleviates the infection of Salmonella, and regulates intestinal flora. Despite this, there have been no genomic studies on this species. Here, we provide the genomic basis for adaptation to the intestinal habitat of this species. We sequenced the genome of L. equi IMAU81196, compared this with published genome information from three strains in NCBI, and analyzed genome characteristics, phylogenetic relationships, and functional genes. The mean genome size of L. equi strains was 2.08 ± 0.09 Mbp, and the mean GC content was 39.17% ± 0.19%. The genome size of L. equi IMAU81196 was 1.95 Mbp, and the GC content was 39.48%. The phylogenetic tree for L. equi based on 1454 core genes showed that the independent branch of strain IMAU81196 was far from the other three strains. In terms of genomic characteristics, single-nucleotide polymorphism (SNP) sites, rapid annotation using subsystem technology (RAST), carbohydrate activity enzymes (CAZy), and predictions of prophage, we showed that strain L. equi JCM 10991T and strain DSM 15833T are not equivalent strains.It is worth mentioning thatthestrain of L. equi has numerous enzymes related to cellulose degradation, and each L. equi strain investigated contained at least one protophage. We speculate that this is the reason why these strains are adapted to the intestinal environment of horses. These results provide new research directions for the future.

Effects of Clostridium butyricum and a Bacteriophage Cocktail on Growth Performance, Serum Biochemistry, Digestive Enzyme Activities, Intestinal Morphology, Immune Responses, and the Intestinal Microbiota in Rabbits

The objective of this study was to assess the effects of dietary supplementation with Clostridium butyricum (CB) and a bacteriophage cocktail (BP) on growth performance, serum biochemical parameters, intestinal digestive and oxidase enzymes, intestinal morphology, immune responses, and the cecum microbiota in rabbits. In total, 108 New Zealand rabbits (5 weeks old) were randomly and equally allotted into three dietary treatment groups (four replicates per treatment, n = 36/treatment): (1) the control (CN) group-rabbits fed the basal diet; (2) CB group-rabbits fed the basal diet supplemented with 100 mg/kg diet Clostridium butyricum; and (3) BP group-rabbits fed the basal diet supplemented with 200 mg/kg diet BP cocktail, respectively, for 6 weeks. Compared with the CN diet, dietary CB and BP inclusion increased the average daily gain (ADG) and average daily feed intake (ADFI) and decreased the feed/gain (F/G) ratio of rabbits. Furthermore, CB increased the digestive enzyme activity (α-amylase and trypsin in the ileum); the chymotrypsin activity was also significantly increased in the duodenum and jejunum. Supplementation with CB significantly enhanced antioxidant capacity (SOD and GSH-Px) in the jejunum and ileum and reduced MDA levels. Additionally, rabbits fed CB had significantly elevated villus height (V) and (V/C) ratios but reduced crypt depth (C). Moreover, dietary CB supplementation markedly increased the ileal expression of tight junction proteins (occludin, ZO-1, and claudin-1) and increased secretory immunoglobulin A (sIgA) production. High-throughput sequencing indicated that the microbiota in the rabbit intestine was altered by CB and BP. Venn diagrams and heatmap plots revealed that the gut microbial community composition varied obviously among rabbits fed different diets. Specifically, CB increased the relative abundance of beneficial bacteria to maintain intestinal barrier homeostasis, whereas BP decreased the relative abundance of Gammaproteobacteria, which included a plenty of pathogenic bacteria.

The Presence of Bacteriophages in the Human Body: Good, Bad or Neutral?

The presence of bacteriophages (phages) in the human body may impact bacterial microbiota and modulate immunity. The role of phages in human microbiome studies and diseases is poorly understood. However, the correlation between a greater abundance of phages in the gut in ulcerative colitis and diabetes has been suggested. Furthermore, most phages found at different sites in the human body are temperate, so their therapeutic effects and their potential beneficial effects remain unclear. Hence, far, no correlation has been observed between the presence of widespread crAssphage in the human population and human health and diseases. Here, we emphasize the beneficial effects of phage transfer in fecal microbiota transplantation (FMT) in Clostridioides difficile infection. The safety of phage use in gastrointestinal disorders has been demonstrated in clinical studies. The significance of phages in the FMT as well as in gastrointestinal disorders remains to be established. An explanation of the multifaceted role of endogenous phages for the development of phage therapy is required.

The mannose phosphotransferase system (Man-PTS) - Mannose transporter and receptor for bacteriocins and bacteriophages

Mannose transporters constitute a superfamily (Man-PTS) of the Phosphoenolpyruvate Carbohydrate Phosphotransferase System (PTS). The membrane complexes are homotrimers of protomers consisting of two subunits, IIC and IID. The two subunits without recognizable sequence similarity assume the same fold, and in the protomer are structurally related by a two fold pseudosymmetry axis parallel to membrane-plane (Liu et al. (2019) Cell Research 29 680). Two reentrant loops and two transmembrane helices of each subunit together form the N-terminal transport domain. Two three-helix bundles, one of each subunit, form the scaffold domain. The protomer is stabilized by a helix swap between these bundles. The two C-terminal helices of IIC mediate the interprotomer contacts. PTS occur in bacteria and archaea but not in eukaryotes. Man-PTS are abundant in Gram-positive bacteria living on carbohydrate rich mucosal surfaces. A subgroup of IICIID complexes serve as receptors for class IIa bacteriocins and as channel for the penetration of bacteriophage lambda DNA across the inner membrane. Some Man-PTS are associated with host-pathogen and -symbiont processes.

CRP-binding bacteriophage as a new element of layer-by-layer assembly carbon nanofiber modified electrodes

Recently, bacteriophage particles have started to be applied as a new biomaterial for developing sensing platforms. They can be used as both a recognition element or/and as building blocks, template/scaffold. In this paper, we studied a bacteriophage selected through phage-display technology. The chosen bacteriophage acted as a building block for creating a carbon nanofiber-based electrode and as a new receptor/binding element that recognizes C-reactive protein (CRP) - one of the markers of inflammatory processes in the human body. The binding efficiency of the selected phage towards CRP is two orders of magnitude higher than in the wild type. We demonstrate that the phage-based sensor is selective against other proteins. Finally, we show that layer-by-layer methods are suitable for deposition of negatively charged phages (wild or CRP-binding) with positively charged carbon nanofibers for electrode surface modification. A three-layered electrode was successfully used for molecular recognition of CRP, and the molecular interactions were studied using electrochemical, biological, and optical methods, including microscopic and spectroscopic analyses.

Phage-Based Sensors in Medicine: A Review

Bacteriophages are interesting entities on the border of biology and chemistry. In nature, they are bacteria parasites, while, after genetic manipulation, they gain new properties, e.g., selectively binding proteins. Owing to this, they may be applied as recognition elements in biosensors. Combining bacteriophages with different transducers can then result in the development of innovative sensor designs that may revolutionize bioanalytics and improve the quality of medical services. Therefore, here, we review the use of bacteriophages, or peptides from bacteriophages, as new sensing elements for the recognition of biomarkers and the construction of the highly effective diagnostics tools.

Honey-bee-associated prokaryotic viral communities reveal wide viral diversity and a profound metabolic coding potential

This study uses viral-like particle purification and subsequent unbiased genome sequencing to identify prokaryotic viruses associated with Apis mellifera. Interestingly, bacteriophages found in honey bees show a high diversity and span different viral taxa. This diversity sharply contrasts with the state-of-the-art knowledge on the relatively simple bee bacterial microbiome. The identification of multiple auxiliary metabolic genes suggests that these bacteriophages possess the coding potential to intervene in essential microbial pathways related to health and possibly also to disease. This study sheds light on a neglected part of the bee microbiota and opens avenues of in vivo research on the interaction of bacteriophages with their bacterial host, which likely has strongly underappreciated consequences on bee health.

Honey bees (Apis mellifera) produce an enormous economic value through their pollination activities and play a central role in the biodiversity of entire ecosystems. Recent efforts have revealed the substantial influence that the gut microbiota exert on bee development, food digestion, and homeostasis in general. In this study, deep sequencing was used to characterize prokaryotic viral communities associated with honey bees, which was a blind spot in research up until now. The vast majority of the prokaryotic viral populations are novel at the genus level, and most of the encoded proteins comprise unknown functions. Nevertheless, genomes of bacteriophages were predicted to infect nearly every major bee-gut bacterium, and functional annotation and auxiliary metabolic gene discovery imply the potential to influence microbial metabolism. Furthermore, undiscovered genes involved in the synthesis of secondary metabolic biosynthetic gene clusters reflect a wealth of previously untapped enzymatic resources hidden in the bee bacteriophage community.

Effect of Baicalin-Aluminum Complexes on Fecal Microbiome in Piglets

The gut microbiome has important effects on gastrointestinal diseases. Diarrhea attenuation functions of baicalin (BA) is not clear. Baicalin-aluminum complexes (BBA) were synthesized from BA, but the BBA's efficacy on the diarrhea of piglets and the gut microbiomes have not been explored and the mechanism remains unclear. This study has explored whether BBA could modulate the composition of the gut microbiomes of piglets during diarrhea. The results showed that the diarrhea rate reduced significantly after treatment with BBA. BBA altered the overall structure of the gut microbiomes. In addition, the Gene Ontology (GO) enrichment analysis indicated that the functional differentially expressed genes, which were involved in the top 30 GO enrichments, were associated with hydrogenase (acceptor) activity, nicotinamide-nucleotide adenylyltransferase activity, and isocitrate lyase activity, belong to the molecular function. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that flagellar assembly, bacterial chemotaxis, lipopolysaccharide biosynthesis, ATP-binding cassette transporters (ABC) transporters, biosynthesis of amino acids, and phosphotransferase system (PTS) were the most enriched during BBA treatment process. Taken together, our results first demonstrated that BBA treatment could modulate the gut microbiomes composition of piglets with diarrhea, which may provide new potential insights on the mechanisms of gut microbiomes associated underlying the antimicrobial efficacy of BBA.

Probiotics: If It Does Not Help It Does Not Do Any Harm. Really?

Probiotics per definition should have beneficial effects on human health, and their consumption has tremendously increased in the last decades. In parallel, the amount of published material and claims for their beneficial efficacy soared continuously. Recently, multiple systemic reviews, meta-analyses, and expert opinions expressed criticism on their claimed effects and safety. The present review describes the dark side of the probiotics, in terms of problematic research design, incomplete reporting, lack of transparency, and under-reported safety. Highlighted are the potential virulent factors and the mode of action in the intestinal lumen, risking the physiological microbiome equilibrium. Finally, regulatory topics are discussed to lighten the heterogeneous guidelines applied worldwide. The shift in the scientific world towards a better understanding of the human microbiome, before consumption of the probiotic cargo, is highly endorsed. It is hoped that better knowledge will extend the probiotic repertoire, re-confirm efficacy or safety, establish their efficacy and substantiate their beneficial effects.

Bacteriophages as Environmental Reservoirs of Antibiotic Resistance

Although antibiotic resistance represents a significant and growing public health concern, the contribution of bacteriophages (phages) to the mobilization of antibiotic resistance genes (ARGs) in the environment has not been extensively studied. Recent studies, however, suggest that phages play an important role in the acquisition, maintenance, and spread of ARGs than previously expected. This Opinion article offers an update on the contribution of phages to environmental antibiotic resistance. A better understanding of the mechanisms and factors that promote antibiotic resistance may significantly contribute to the implementation of control strategies.

Engineered K1F bacteriophages kill intracellular Escherichia coli K1 in human epithelial cells

Bacterial infections can be treated with bacteriophages that show great specificity towards their bacterial host and can be genetically modified for different applications. However, whether and how bacteriophages can kill intracellular bacteria in human cells remains elusive. Here, using CRISPR/Cas selection, we have engineered a fluorescent bacteriophage specific for E. coli K1, a nosocomial pathogen responsible for urinary tract infections, neonatal meningitis and sepsis. By confocal and live microscopy, we show that engineered bacteriophages K1F-GFP and E. coli EV36-RFP bacteria displaying the K1 capsule, enter human cells via phagocytosis. Importantly, we show that bacteriophage K1F-GFP efficiently kills intracellular E. coli EV36-RFP in T24 human urinary bladder epithelial cells. Finally, we provide evidence that bacteria and bacteriophages are degraded by LC3-associated phagocytosis and xenophagy.

Bacteriophages: A Therapy Concept against Multi-Drug-Resistant Bacteria

Bacteriophages (phages) are viruses that kill bacteria specifically but cannot infect other kinds of organisms. They have attracted new attention since the increasing antibiotic resistance developed into a global crisis. Phage therapy, a 100-year-old form of antibacterial treatment in medicine, is gaining momentum because phages represent a therapy concept without such negative side effects as toxicity; phages are the only therapeutic agent that regulates itself at the sites of infection and decays when the infectious bacteria have been killed. Nature is an almost infinite phage resource: New ones can be isolated for most kinds of problem bacteria as needed; bacteria and their phages constantly co-evolve. This is important as new pathogenic bacterial variants evolve and new challenging situations arise. In human therapy, "cocktails" of multiple phages may reduce the probability of selecting bacteria that developed resistance to a certain phage. Antibiotic agents can be applied together with phages in many circumstances; the two often function synergistically. Phages cannot be expected to replace antibiotic agents in our medical arsenal, but can be used where antibiotic agents fail. The selected phages, however, must be obligately virulent, well-characterized, and highly purified before application. Countless patients and their physicians are waiting for re-establishing phage therapy as a flexible, tailored medicine; infrastructures should be built in all countries urgently: The 2015 World Health Organization assembly resolution 68.7.3. called for national action plans by May 2017 to combat the antimicrobial drug resistance crisis. This article discusses the therapeutic potential of phages and describes challenges and recent developments.

Human gut microbiome: hopes, threats and promises

The microbiome has received increasing attention over the last 15 years. Although gut microbes have been explored for several decades, investigations of the role of microorganisms that reside in the human gut has attracted much attention beyond classical infectious diseases. For example, numerous studies have reported changes in the gut microbiota during not only obesity, diabetes, and liver diseases but also cancer and even neurodegenerative diseases. The human gut microbiota is viewed as a potential source of novel therapeutics. Between 2013 and 2017, the number of publications focusing on the gut microbiota was, remarkably, 12 900, which represents four-fifths of the total number of publications over the last 40 years that investigated this topic. This review discusses recent evidence of the impact of the gut microbiota on metabolic disorders and focus on selected key mechanisms. This review also aims to provide a critical analysis of the current knowledge in this field, identify putative key issues or problems and discuss misinterpretations. The abundance of metagenomic data generated on comparing diseased and healthy subjects can lead to the erroneous claim that a bacterium is causally linked with the protection or the onset of a disease. In fact, environmental factors such as dietary habits, drug treatments, intestinal motility and stool frequency and consistency are all factors that influence the composition of the microbiota and should be considered. The cases of the bacteria Prevotella copri and Akkermansia muciniphila will be discussed as key examples.