The human body hosts vast microbial communities, termed the microbiome. Less well known is the fact that the human body also hosts vast numbers of different viruses, collectively termed the 'virome'. ...Viruses are believed to be the most abundant and diverse biological entities on our planet, with an estimated 10
particles on Earth. The human virome is similarly vast and complex, consisting of approximately 10
particles per human individual, with great heterogeneity. In recent years, studies of the human virome using metagenomic sequencing and other methods have clarified aspects of human virome diversity at different body sites, the relationships to disease states and mechanisms of establishment of the human virome during early life. Despite increasing focus, it remains the case that the majority of sequence data in a typical virome study remain unidentified, highlighting the extent of unexplored viral 'dark matter'. Nevertheless, it is now clear that viral community states can be associated with adverse outcomes for the human host, whereas other states are characteristic of health. In this Review, we provide an overview of research on the human virome and highlight outstanding recent studies that explore the assembly, composition and dynamics of the human virome as well as host-virome interactions in health and disease.
Integration of new DNA into a cellular chromosome can alter the activity of nearby genes, sometimes affecting subsequent cell growth. A potent form of insertional mutagenesis involves integration of ...retroviral DNA produced by reverse transcription, a required step in the replication of retroviruses. In recent years retroviral replication has been adapted to allow new gene addition by retroviral vectors. Early in the history of retrovirus research, analysis of insertional mutagenesis in laboratory animals was found at times to result in transformation, leading to the discovery of cellular proto-oncogenes. In-depth analysis of the genetic consequences showed that integration of retroviral DNA could alter the gene activity in a variety of ways. Mechanisms of retroviral insertional mutagenesis in humans are much less well documented. However, recent work from the gene therapy and HIV fields now specify four genetic mechanisms of retroviral insertional mutagenesis in humans: (1) gene activation by integration of an enhancer sequence encoded in a retroviral vector (enhancer insertion), (2) gene activation by promoter insertion, (3) gene inactivation by insertional disruption, and (4) gene activation by mRNA 3′ end substitution. In each example, integration in patients was associated with clonal expansion or frank transformation.
In mammals, multiple physiological, metabolic, and behavioral processes are subject to circadian rhythms, adapting to changing light in the environment. Here we analyzed circadian rhythms in the ...fecal microbiota of mice using deep sequencing, and found that the absolute amount of fecal bacteria and the abundance of Bacteroidetes exhibited circadian rhythmicity, which was more pronounced in female mice. Disruption of the host circadian clock by deletion ofBmal1, a gene encoding a core molecular clock component, abolished rhythmicity in the fecal microbiota composition in both genders.Bmal1deletion also induced alterations in bacterial abundances in feces, with differential effects based on sex. Thus, although host behavior, such as time of feeding, is of recognized importance, here we show that sex interacts with the host circadian clock, and they collectively shape the circadian rhythmicity and composition of the fecal microbiota in mice.
Diet influences health as a source of nutrients and toxins, and by shaping the composition of resident microbial populations. Previous studies have begun to map out associations between diet and the ...bacteria and viruses of the human gut microbiome. Here we investigate associations of diet with fungal and archaeal populations, taking advantage of samples from 98 well-characterized individuals. Diet was quantified using inventories scoring both long-term and recent diet, and archaea and fungi were characterized by deep sequencing of marker genes in DNA purified from stool. For fungi, we found 66 genera, with generally mutually exclusive presence of either the phyla Ascomycota or Basiodiomycota. For archaea, Methanobrevibacter was the most prevalent genus, present in 30% of samples. Several other archaeal genera were detected in lower abundance and frequency. Myriad associations were detected for fungi and archaea with diet, with each other, and with bacterial lineages. Methanobrevibacter and Candida were positively associated with diets high in carbohydrates, but negatively with diets high in amino acids, protein, and fatty acids. A previous study emphasized that bacterial population structure was associated primarily with long-term diet, but high Candida abundance was most strongly associated with the recent consumption of carbohydrates. Methobrevibacter abundance was associated with both long term and recent consumption of carbohydrates. These results confirm earlier targeted studies and provide a host of new associations to consider in modeling the effects of diet on the gut microbiome and human health.
Abnormal composition of intestinal bacteria—“dysbiosis”—is characteristic of Crohn’s disease. Disease treatments include dietary changes and immunosuppressive anti-TNFα antibodies as well as ...ancillary antibiotic therapy, but their effects on microbiota composition are undetermined. Using shotgun metagenomic sequencing, we analyzed fecal samples from a prospective cohort of pediatric Crohn’s disease patients starting therapy with enteral nutrition or anti-TNFα antibodies and reveal the full complement and dynamics of bacteria, fungi, archaea, and viruses during treatment. Bacterial community membership was associated independently with intestinal inflammation, antibiotic use, and therapy. Antibiotic exposure was associated with increased dysbiosis, whereas dysbiosis decreased with reduced intestinal inflammation. Fungal proportions increased with disease and antibiotic use. Dietary therapy had independent and rapid effects on microbiota composition distinct from other stressor-induced changes and effectively reduced inflammation. These findings reveal that dysbiosis results from independent effects of inflammation, diet, and antibiotics and shed light on Crohn disease treatments.
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•Inflammation, antibiotics, and diet independently affect microbiota in Crohn’s disease•Antibiotics are associated with bacterial dysbiosis and increased fungi•Dysbiosis decreases with reduction in intestinal inflammation•Diet has an independent and rapid effect on gut microbiota composition
Intestinal microbiota dysbiosis is characteristic of Crohn’s disease, but the contributing factors remain unclear. By examining pediatric Crohn’s disease patients, Lewis et al. show that dysbiosis is independently associated with antibiotics, inflammation, and diet and decreases with reduced intestinal inflammation. These results may facilitate biomarker discovery and therapeutic interventions.
Antibiotic use in humans has been associated with outgrowth of fungi. Here we used a murine model to investigate the gut microbiome over 76 days of treatment with vancomycin, ampicillin, neomycin, ...and metronidazole and subsequent recovery. Mouse stool was studied as a surrogate for the microbiota of the lower gastrointestinal tract. The abundance of fungi and bacteria was measured using quantitative PCR, and the proportional composition of the communities quantified using 454/Roche pyrosequencing of rRNA gene tags. Prior to treatment, bacteria outnumbered fungi by >3 orders of magnitude. Upon antibiotic treatment, bacteria dropped in abundance >3 orders of magnitude, so that the predominant 16S sequences detected became transients derived from food. Upon cessation of treatment, bacterial communities mostly returned to their previous numbers and types after 8 weeks, though communities remained detectably different from untreated controls. Fungal communities varied substantially over time, even in the untreated controls. Separate cages within the same treatment group showed radical differences, but mice within a cage generally behaved similarly. Fungi increased ∼40-fold in abundance upon antibiotic treatment but declined back to their original abundance after cessation of treatment. At the last time point, Candida remained more abundant than prior to treatment. These data show that 1) gut fungal populations change radically during normal mouse husbandry, 2) fungi grow out in the gut upon suppression of bacterial communities with antibiotics, and 3) perturbations due to antibiotics persist long term in both the fungal and bacterial microbiota.
Rapid evolution of the human gut virome Minot, Samuel; Bryson, Alexandra; Chehoud, Christel ...
Proceedings of the National Academy of Sciences,
07/2013, Letnik:
110, Številka:
30
Journal Article
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Humans are colonized by immense populations of viruses, which metagenomic analysis shows are mostly unique to each individual. To investigate the origin and evolution of the human gut virome, we ...analyzed the viral community of one adult individual over 2.5 y by extremely deep metagenomic sequencing (56 billion bases of purified viral sequence from 24 longitudinal fecal samples). After assembly, 478 well-determined contigs could be identified, which are inferred to correspond mostly to previously unstudied bacteriophage genomes. Fully 80% of these types persisted throughout the duration of the 2.5-y study, indicating long-term global stability. Mechanisms of base substitution, rates of accumulation, and the amount of variation varied among viral types. Temperate phages showed relatively lower mutation rates, consistent with replication by accurate bacterial DNA polymerases in the integrated prophage state. In contrast, Microviridae, which are lytic bacteriophages with single-stranded circular DNA genomes, showed high substitution rates (>10 ⁻⁵ per nucleotide each day), so that sequence divergence over the 2.5-y period studied approached values sufficient to distinguish new viral species. Longitudinal changes also were associated with diversity-generating retroelements and virus-encoded Clustered Regularly Interspaced Short Palindromic Repeats arrays. We infer that the extreme interpersonal diversity of human gut viruses derives from two sources, persistence of a small portion of the global virome within the gut of each individual and rapid evolution of some long-term virome members.
Pioneering gene therapy trials have shown that the genetic engineering of haematopoietic stem and progenitor cells can be an alternative to allogeneic transplantation in the treatment of primary ...immunodeficiencies. Early trials also highlighted the risk of insertional mutagenesis and oncogene transactivation associated with the first generation of gammaretroviral vectors. These events prompted the development of safer, self-inactivating lentiviral or gammaretroviral vectors. These lentiviral vectors have been successfully used to treat over 200 patients with 10 different haematological disorders (including primary immunodeficiencies, haemoglobinopathies and metabolic disorders) and for the generation of chimeric antigen receptor-T cells for cancer therapy. However, several challenges, such as effective reconstitution during inflammation, remain if gene therapy is to be extended to more complex diseases in which haematopoietic stem and progenitor cells can be altered by the disease environment. We discuss the progress made and future challenges for gene therapy and contrast gene therapy with gene-editing strategies.
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