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Background The human microbiome plays an important role in cancer. Accumulating evidence indicates that commensal microbiome-derived DNA may be represented in minute quantities in the cell-free DNA of human blood and could possibly be harnessed as a new cancer biomarker. However, there has been limited use of rigorous experimental controls to account for contamination, which invariably affects low-biomass microbiome studies. Results We apply a combination of 16S-rRNA-gene sequencing and droplet digital PCR to determine if the specific detection of cell-free microbial DNA (cfmDNA) is possible in metastatic melanoma patients. Compared to matched stool and saliva samples, the absolute concentration of cfmDNA is low but significantly above the levels detected from negative controls. The microbial community of plasma is strongly influenced by laboratory and reagent contaminants introduced during the DNA extraction and sequencing processes. Through the application of an in silico decontamination strategy including the filtering of amplicon sequence variants (ASVs) with batch dependent abundances and those with a higher prevalence in negative controls, we identify known gut commensal bacteria, such as Faecalibacterium , Bacteroides and Ruminococcus , and also other uncharacterised ASVs. We analyse additional plasma samples, highlighting the potential of this framework to identify differences in cfmDNA between healthy and cancer patients. Conclusions Together, these observations indicate that plasma can harbour a low yet detectable level of cfmDNA. The results highlight the importance of accounting for contamination and provide an analytical decontamination framework to allow the accurate detection of cfmDNA for future biomarker studies in cancer and other diseases.

Faecalibacterium has recently garnered attention for its potential health implications. To better understand its role, we developed and assessed real‐time PCR assays for detecting and quantifying various Faecalibacterium species in human stool samples from both healthy individuals and Crohn's disease patients, either in flare or remission. The assays targeted the Microbial Anti‐inflammatory Molecule (MAM) genes, which encode MAM proteins. These assays demonstrated 100% species‐specificity using strains from six Faecalibacterium species: Faecalibacterium prausnitzii , Faecalibacterium taiwanense , Faecalibacterium duncaniae , Faecalibacterium longum , Faecalibacterium hattori , and Faecalibacterium CNCM4541 . They also showed high sensitivity with detection limits of 10^5 bacteria per gram of sample. In healthy individuals, the different Faecalibacterium species varied in abundance. F . taiwanense , F . duncaniae , and F . longum were the most prevalent, around 10^10 bacteria/g of stool. In contrast, F . hattori and CNCM4541 were less abundant, with 10^7 bacteria/g. Despite its low abundance, F . hattori was present in all healthy subjects, while CNCM4541 was detected in only 50% of them. Notably, F . taiwanense , F . duncaniae , and F . longum were found in all healthy individuals. In Crohn's disease patients, both in flare and remission, a decrease in Faecalibacterium species was observed, with no recovery in remission. The most abundant species in Crohn's disease patients were F . prausnitzii and F . duncaniae , around 10^7 bacteria/g, while F . longum , F . hattori , and F . taiwanense were present at lower levels (10^6 bacteria/g), and CNCM4541 was no longer detected. Interestingly, F . prausnitzii showed a smaller decrease in abundance compared with other species. Moreover, F . prausnitzii was significantly more prevalent in patients in remission than in those in flare, suggesting that it may be more resistant to inflammation. These findings highlight the importance of accurately characterizing and quantifying Faecalibacterium species to better understand their role in health and disease.

Dysbiosis, or imbalance in the gut microbiome, has been implicated in auto-immune, inflammatory, neurological diseases as well as in cancers. More recently it has also been shown to be associated with ocular diseases. In the present study, the association of gut microbiome dysbiosis with bacterial Keratitis, an inflammatory eye disease which significantly contributes to corneal blindness, was investigated. Bacterial and fungal gut microbiomes were analysed using fecal samples of healthy controls (HC, n = 21) and bacterial Keratitis patients (BK, n = 19). An increase in abundance of several anti-inflammatory organisms including Dialister, Megasphaera, Faecalibacterium, Lachnospira, Ruminococcus and Mitsuokella and members of Firmicutes, Veillonellaceae, Ruminococcaceae and Lachnospiraceae was observed in HC compared to BK patients in the bacterial microbiome. In the fungal microbiome, a decrease in the abundance of Mortierella, Rhizopus, Kluyveromyces, Embellisia and Haematonectria and an increase in the abundance of pathogenic fungi Aspergillus and Malassezia were observed in BK patients compared to HC. In addition, heatmaps, PCoA plots and inferred functional profiles also indicated significant variations between the HC and BK microbiomes, which strongly suggest dysbiosis in the gut microbiome of BK patients. This is the first study demonstrating the association of gut microbiome with the pathophysiology of BK and thus supports the gut–eye axis hypothesis. Considering that Keratitis affects about 1 million people annually across the globe, the data could be the basis for developing alternate strategies for treatment like use of probiotics or fecal transplantation to restore the healthy microbiome as a treatment protocol for Keratitis.

Background Anxiety and depression are complications in Irritable bowel syndrome (IBS) patients. In this study, we recruited 18 IBS patients with mild-modest anxiety and depression behaviors, and after the screening, we defined the FMT treatment group (n = 9) and the control group (n = 9). The IBS symptom severity scale (IBS-SSS), Hamilton Anxiety Rating Scale (HAM-A), Hamilton Depression Rating Scale (HAM-D), Irritable Bowel Syndrome Quality of Life (IBS-QOL) and Bristol stool scale (BSS) were evaluated one week before FMT (baseline), one-week-, one-month-, two-month-, and three-month-following FMT. Meanwhile, we determined the SCFAs in the patient’s feces and serum and continued the metagenomic analysis of the microorganisms in the patient’s feces. Results The results showed that the patient’s anxiety and depression behavior gradually improved with FMT treatment. Moreover, the illness and quality of life had also been relieved significantly. The content of isovaleric acid and valeric acid was significantly reduced in the FMT group compared to the Col group. Metagenomic analysis showed that FMT treatment decreased the abundance of Faecalibacterium, Eubacterium and Escherichia . From KEGG functional analysis, we confirmed that the top five abundant pathways were “bacterial chemotaxis, “flagellar assembly”, “glycine, serine and threonine metabolism”, “apoptosis”, and “bacterial invasion of epithelial cells”. Conclusions FMT treatment can effectively alleviate the anxiety and depression behaviors of IBS-D patients and reduce the IBS-SSS score, indicating that FMT can improve patients’ symptoms. The high throughput sequencing results show that Bifidobacterium and Escherichia play the most critical role in the formation and recovery of IBS-D patients. The GC/MS data indicated that faeces isovaleric acid and valeric acid might be more suitable as a metabolic indicator of IBS-D remission. Trial registration  ChiCTR, ChiCTR1900024924, Registered 3 August 2019, https://www.chictr.org.cn/showproj.aspx?proj=41676 .

An analysis of fecal microbiome data from individuals in the United States, United Kingdom, and Mexico shows that associations with dietary components vary both by country and by level of resolution (i.e., genus and strain). Our work sheds light on why there may be conflicting reports regarding microbial associations with diet, disease, and health.

Gastro-Oesophageal Reflux (GOR) is a key problem in Cystic Fibrosis (CF), but the relationship between lung and gastric microbiomes is not well understood. We hypothesised that CF gastric and lung microbiomes are related. Gastric and sputum cultures were obtained from fifteen CF patients receiving percutaneous endoscopic gastrostomy feeding. Non-CF gastric juice data was obtained through endoscopy from 14 patients without lung disease. Bacterial and fungal isolates were identified by culture. Molecular bacterial profiling used next generation sequencing (NGS) of the 16S rRNA gene. Cultures grew bacteria and/or fungi in all CF gastric juice and sputa and in 9/14 non-CF gastric juices. Pseudomonas aeruginosa(Pa) was present in CF sputum in 11 patients, 4 had identical Pa strains in the stomach. NGS data from non-CF gastric juice samples were significantly more diverse compared to CF samples. NGS showed CF gastric juice had markedly lower abundance of normal gut bacteria; Bacteroides and Faecalibacterium, but increased Pseudomonas compared with non-CF. Multivariate partial least squares discriminant analysis demonstrated similar bacterial profiles of CF sputum and gastric juice samples, which were distinct from non-CF gastric juice. We provide novel evidence suggesting the existence of an aerodigestive microbiome in CF, which may have clinical relevance.

Background Faecalibacterium prausnitzii is a ubiquitous member of the human gut microbiome, constituting up to 15% of the total bacteria in the human gut. Substantial evidence connects decreased levels of F. prausnitzii with the onset and progression of certain forms of inflammatory bowel disease, which has been attributed to its anti-inflammatory potential. Two phylogroups of F. prausnitzii have been identified, with a decrease in phylogroup I being a more sensitive marker of intestinal inflammation. Much of the genomic and physiological data available to date was collected using phylogroup II strains. Little analysis of F. prausnitzii genomes has been performed so far and genetic differences between phylogroups I and II are poorly understood. Results In this study we sequenced 11 additional F. prausnitzii genomes and performed comparative genomics to investigate intraspecies diversity, functional gene complement and the mobilome of 31 high-quality draft and complete genomes. We reveal a very low level of average nucleotide identity among F. prausnitzii genomes and a high level of genome plasticity. Two genomogroups can be separated based on differences in functional gene complement, albeit that this division does not fully agree with separation based on conserved gene phylogeny, highlighting the importance of horizontal gene transfer in shaping F. prausnitzii genomes. The difference between the two genomogroups is mainly in the complement of genes associated with catabolism of carbohydrates (such as a predicted sialidase gene in genomogroup I) and amino acids, as well as defense mechanisms. Conclusions Based on the combination of ANI of genomic sequences, phylogenetic analysis of core proteomes and functional differences we propose to separate the species F. prausnitzii into two new species level taxa: F. prausnitzii sensu stricto (neotype strain A2–165 T  = DSM 17677 T  = JCM 31915 T ) and F. moorei sp. nov. (type strain ATCC 27768 T  = NCIMB 13872 T ).

Background The aim was to evaluate the changes of 16S rDNA sequencing and LC-MS metabolomics in breast cancer and explore the growth inhibition of breast cancer cells by Faecalibacterium prausnitzii . Results Total 49 significantly different flora and 26 different metabolites were screened between two groups, and the correlation was calculated. Relative abudance of Firmicutes and Bacteroidetes were decreased, while relative abundance of verrucomicrobla , proteobacteria and actinobacteria was increased in breast cancer group. Differentially expressed metabolites were mainly enriched in pathways such as linoleic acid metabolism, retrograde endocannabinoid signaling, biosynthesis of unsaturated fatty acids, choline metabolism in cancer and arachidonic acid metabolism. Lipid upregulation was found in breast cancer patients, especially phosphorocholine. The abundance of Faecalibacterium was reduced in breast cancer patients, which was negatively correlated with various phosphorylcholines. Moreover, Faecalibacterium prausnitzii , the most well-known species in Faecalibacterium genus, could inhibit the secretion of interleukin-6 (IL-6) and the phosphorylation of Janus kinases 2 (JAK2)/signal transducers and activators of transcription 3 (STAT3) in breast cancer cells. Faecalibacterium prausnitzii also suppressed the proliferation and invasion and promoted the apoptosis of breast cancer cells, while these effects disappeared after adding recombinant human IL-6. Conclusions Flora-metabolites combined with the flora-bacteria (such as Faecalibacterium combined with phosphorocholine) might a new detection method for breast cancer. Faecalibacterium may be helpful for prevention of breast cancer. Faecalibacterium prausnitzii suppresses the growth of breast cancer cells through inhibition of IL-6/STAT3 pathway.

Commensal butyrate-producing bacteria belonging to the Firmicutes phylum are abundant in the human gut and are crucial for maintaining health. Currently, insight is lacking into how they target otherwise indigestible dietary fibers and into the trophic interactions they establish with other glycan degraders in the competitive gut environment. β-Mannans are hemicelluloses that are abundant in modern diets as components in seed endosperms and common additives in processed food. Currently, the collective understanding of β-mannan saccharification in the human colon is limited to a few keystone species, which presumably liberate low-molecular-weight mannooligosaccharide fragments that become directly available to the surrounding microbial community. Here, we show that a dominant butyrate producer in the human gut, Faecalibacterium prausnitzii , is able to acquire and degrade various β-mannooligosaccharides (β-MOS), which are derived by the primary mannanolytic activity of neighboring gut microbiota. Detailed biochemical analyses of selected protein components from their two β-MOS utilization loci ( F. prausnitzii β-MOS utilization loci [ Fp MULs]) supported a concerted model whereby the imported β-MOS are stepwise disassembled intracellularly by highly adapted enzymes. Coculturing experiments of F. prausnitzii with the primary degraders Bacteroides ovatus and Roseburia intestinalis on polymeric β-mannan resulted in syntrophic growth, thus confirming the high efficiency of the Fp MULs’ uptake system. Genomic comparison with human F. prausnitzii strains and analyses of 2,441 public human metagenomes revealed that Fp MULs are highly conserved and distributed worldwide. Together, our results provide a significant advance in the knowledge of β-mannan metabolism and the degree to which its degradation is mediated by cross-feeding interactions between prominent beneficial microbes in the human gut. IMPORTANCE Commensal butyrate-producing bacteria belonging to the Firmicutes phylum are abundant in the human gut and are crucial for maintaining health. Currently, insight is lacking into how they target otherwise indigestible dietary fibers and into the trophic interactions they establish with other glycan degraders in the competitive gut environment. By combining cultivation, genomic, and detailed biochemical analyses, this work reveals the mechanism enabling F. prausnitzii , as a model Ruminococcaceae within Firmicutes , to cross-feed and access β-mannan-derived oligosaccharides released in the gut ecosystem by the action of primary degraders. A comprehensive survey of human gut metagenomes shows that Fp MULs are ubiquitous in human populations globally, highlighting the importance of microbial metabolism of β-mannans/β-MOS as a common dietary component. Our findings provide a mechanistic understanding of the β-MOS utilization capability by F. prausnitzii that may be exploited to select dietary formulations specifically boosting this beneficial symbiont, and thus butyrate production, in the gut.

Background The study of the gut microbiota (GM) is rapidly moving towards its functional characterization by means of shotgun meta-omics. In this context, there is still no consensus on which microbial functions are consistently and constitutively expressed in the human gut in physiological conditions. Here, we selected a cohort of 15 healthy subjects from a native and highly monitored Sardinian population and analyzed their GMs using shotgun metaproteomics, with the aim of investigating GM functions actually expressed in a healthy human population. In addition, shotgun metagenomics was employed to reveal GM functional potential and to compare metagenome and metaproteome profiles in a combined taxonomic and functional fashion. Results Metagenomic and metaproteomic data concerning the taxonomic structure of the GM under study were globally comparable. On the contrary, a considerable divergence between genetic potential and functional activity of the human healthy GM was observed, with the metaproteome displaying a higher plasticity, compared to the lower inter-individual variability of metagenome profiles. The taxon-specific contribution to functional activities and metabolic tasks was also examined, giving insights into the peculiar role of several GM members in carbohydrate metabolism (including polysaccharide degradation, glycan transport, glycolysis, and short-chain fatty acid production). Noteworthy, Firmicutes-driven butyrogenesis (mainly due to Faecalibacterium spp.) was shown to be the metabolic activity with the highest expression rate and the lowest inter-individual variability in the study cohort, in line with the previously reported importance of the biosynthesis of this microbial product for the gut homeostasis. Conclusions Our results provide detailed and taxon-specific information regarding functions and pathways actively working in a healthy GM. The reported discrepancy between expressed functions and functional potential suggests that caution should be used before drawing functional conclusions from metagenomic data, further supporting metaproteomics as a fundamental approach to characterize the human GM metabolic functions and activities.