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Recent studies highlight the importance of intestinal fungal microbiota in the development of human disease. Infants, in particular, are an important population in which to study intestinal microbiomes because microbial community structure and dynamics during this formative window of life have the potential to influence host immunity and metabolism. When compared to bacteria, much less is known about the early development of human fungal communities, owing partly to their lower abundance and the relative lack of established molecular and taxonomic tools for their study. Herein, we describe the development, validation, and use of complementary amplicon-based genomic strategies to characterize infant fungal communities and provide quantitative information about Candida, an important fungal genus with respect to intestinal colonization and human disease. Fungal communities were characterized from 11 infant fecal samples using primers that target the internal transcribed spacer (ITS) 2 locus, a region that provides taxonomic discrimination of medically relevant fungi. Each sample yielded an average of 27,553 fungal sequences and Candida albicans was the most abundant species identified by sequencing and quantitative PCR (qPCR). Low numbers of Candida krusei and Candida parapsilosis sequences were observed in several samples, but their presence was detected by species-specific qPCR in only one sample, highlighting a challenge inherent in the study of low-abundance organisms. Overall, the sequencing results revealed that infant fecal samples had fungal diversity comparable to that of bacterial communities in similar-aged infants, which correlated with the relative abundance of C. albicans. We conclude that targeted sequencing of fungal ITS2 amplicons in conjunction with qPCR analyses of specific fungi provides an informative picture of fungal community structure in the human intestinal tract. Our data suggests that the infant intestine harbors diverse fungal species and is consistent with prior culture-based analyses showing that the predominant fungus in the infant intestine is C. albicans.

Several bacterial taxa enriched in inflammatory bowel diseases and colorectal cancer (CRC) are found in the oral cavity. We conducted a pilot study nested within a six-week aspirin intervention in a randomized placebo-controlled trial to test their response to aspirin intervention. Fifty healthy subjects, 50–75 years old, were randomized to receive 325 mg aspirin (n = 30) or placebo (n = 20) orally once daily for six weeks. Oral tongue swabs were collected at baseline and week six. We estimated the association between aspirin use and the temporal changes in the relative abundance of pre-specified genus level taxa from pre- to post-treatment. The temporal change in relative abundance differed for eight genus level taxa between the aspirin and placebo groups. In the aspirin group, there were significant increases in the relative abundances of Neisseria, Streptococcus, Actinomyces, and Rothia and significant decreases in Prevotella, Veillonella, Fusobacterium, and Porphyromonas relative to placebo. The log ratio of Neisseria to Fusobacterium declined more in the aspirin group than placebo, signaling a potential marker associated with aspirin intervention. These preliminary findings should be validated using metagenomic sequencing and may guide future studies on the role of aspirin on taxa in various oral ecological niches.

Abstract The genome sequence of the obligate chemolithoautotroph Hydrogenovibrio crunogenus paradoxically predicts a complete oxidative citric acid cycle (CAC). This prediction was tested by multiple approaches including whole cell carbon assimilation to verify obligate autotrophy, phylogenetic analysis of CAC enzyme sequences and enzyme assays. Hydrogenovibrio crunogenus did not assimilate any of the organic compounds provided (acetate, succinate, glucose, yeast extract, tryptone). Enzyme activities confirmed that its CAC is mostly uncoupled from the NADH pool. 2-Oxoglutarate:ferredoxin oxidoreductase activity is absent, though pyruvate:ferredoxin oxidoreductase is present, indicating that sequence-based predictions of substrate for this oxidoreductase were incorrect, and that H. crunogenus may have an incomplete CAC. Though the H. crunogenus CAC genes encode uncommon enzymes, the taxonomic distribution of their top matches suggests that they were not horizontally acquired. Comparison of H. crunogenus CAC genes to those present in other ‘Proteobacteria’ reveals that H. crunogenus and other obligate autotrophs lack the functional redundancy for the steps of the CAC typical for facultative autotrophs and heterotrophs, providing another possible mechanism for obligate autotrophy. Central carbon metabolism in Hydrogenovibrio crunogenus from deep-sea hydrothermal vents.

Recent studies highlight the importance of intestinal fungal microbiota in the development of human disease. Infants, in particular, are an important population in which to study intestinal microbiomes because microbial community structure and dynamics during this formative window of life have the potential to influence host immunity and metabolism. When compared to bacteria, much less is known about the early development of human fungal communities, owing partly to their lower abundance and the relative lack of established molecular and taxonomic tools for their study. Herein, we describe the development, validation, and use of complementary amplicon-based genomic strategies to characterize infant fungal communities and provide quantitative information about Candida, an important fungal genus with respect to intestinal colonization and human disease. Fungal communities were characterized from 11 infant fecal samples using primers that target the internal transcribed spacer (ITS) 2 locus, a region that provides taxonomic discrimination of medically relevant fungi. Each sample yielded an average of 27,553 fungal sequences and Candida albicans was the most abundant species identified by sequencing and quantitative PCR (qPCR). Low numbers of Candida krusei and Candida parapsilosis sequences were observed in several samples, but their presence was detected by species-specific qPCR in only one sample, highlighting a challenge inherent in the study of low-abundance organisms. Overall, the sequencing results revealed that infant fecal samples had fungal diversity comparable to that of bacterial communities in similar-aged infants, which correlated with the relative abundance of C. albicans. We conclude that targeted sequencing of fungal ITS2 amplicons in conjunction with qPCR analyses of specific fungi provides an informative picture of fungal community structure in the human intestinal tract. Our data suggests that the infant intestine harbors diverse fungal species and is consistent with prior culture-based analyses showing that the predominant fungus in the infant intestine is C. albicans.

Colorectal cancer (CRC) progression is driven by a series of sequential mutations in key driver genes, yet the factors underpinning tumor advancement and metastasis remain incompletely understood. Mutations in TP53 and SMAD4, in particular, are associated with poor treatment response and enhanced CRC pathogenesis. Although gut microbiome dysbiosis is implicated in CRC initiation and inflammation, the interactions between the microbiome and specific CRC driver mutations, especially those promoting metastasis, are poorly defined. In this study, we used triple mutant (Apc, Kras, Tp53; AKP) and quadruple mutant (Apc, Kras, Tp53, Smad4; AKPS) organoid-based orthotopic mouse models of CRC to examine the impact of SMAD4 mutation on tumor progression, metastasis, and microbiome composition. AKP and AKPS organoids were endoscopically implanted into the colons of individually housed C57BL/6 mice, and fecal samples were collected weekly over an 8-week period. Our results reveal significant differences in metastatic potential and microbial community dynamics between the two tumor models. AKPS tumors exhibited metastasis to the lymph nodes, liver, and lungs, whereas AKP tumors remained confined to the colon. Longitudinal microbiome analysis showed shifts in microbial composition within each tumor model. Both AKP and AKPS models demonstrated enrichment of Faecalibaculum and a decrease in Dubosiella over time; however, additional shifts were observed with distinct taxa associated with late-stage tumors in each group. Notably, the AKPS model exhibited higher relative abundances of pro-inflammatory taxa, including Turicibacter, Romboutsia, and Akkermansia, suggesting that SMAD4 mutation promotes a more immunosuppressive and pro-metastatic microbiome profile. These findings underscore the role of SMAD4 in modulating the microbiome in a manner that favors CRC metastasis and suggests potential microbial targets for therapeutic intervention to slow CRC progression. This work provides new insights into the microbiomes role in CRC mutagenesis and metastasis, highlighting the interplay between host genetics and gut microbiota in driving cancer aggressiveness.Competing Interest StatementThe authors have declared no competing interest.

Mendelian randomization (MR) is an epidemiological technique that uses genetic variants to distinguish correlation from causation in observational data. The reliability of a MR investigation depends on the validity of the genetic variants as instrumental variables (IVs). We develop the contamination mixture method, a method for MR with two modalities. First, it identifies groups of genetic variants with similar causal estimates, which may represent distinct mechanisms by which the risk factor influences the outcome. Second, it performs MR robustly and efficiently in the presence of invalid IVs. Compared to other robust methods, it has the lowest mean squared error across a range of realistic scenarios. The method identifies 11 variants associated with increased high-density lipoprotein-cholesterol, decreased triglyceride levels, and decreased coronary heart disease risk that have the same directions of associations with various blood cell traits, suggesting a shared mechanism linking lipids and coronary heart disease risk mediated via platelet aggregation. Mendelian randomization (MR) is a method for inferring causal relationships between risk factors and outcomes via associated genetic variants. Here, Burgess et al. develop the contamination mixture method which yields robust MR results in the presence of invalid instrumental variables and groups variants by their effect estimates.

Genome-wide association studies (GWAS) have identified thousands of genomic regions affecting complex diseases. The next challenge is to elucidate the causal genes and mechanisms involved. One approach is to use statistical colocalization to assess shared genetic aetiology across multiple related traits (e.g. molecular traits, metabolic pathways and complex diseases) to identify causal pathways, prioritize causal variants and evaluate pleiotropy. We propose HyPrColoc (Hypothesis Prioritisation for multi-trait Colocalization), an efficient deterministic Bayesian algorithm using GWAS summary statistics that can detect colocalization across vast numbers of traits simultaneously (e.g. 100 traits can be jointly analysed in around 1 s). We perform a genome-wide multi-trait colocalization analysis of coronary heart disease (CHD) and fourteen related traits, identifying 43 regions in which CHD colocalized with ≥1 trait, including 5 previously unknown CHD loci. Across the 43 loci, we further integrate gene and protein expression quantitative trait loci to identify candidate causal genes. Statistical colocalisation is a method to identify causal genes and shared genetic aetiology across traits. Here, the authors describe HyPrColoc, an efficient Bayesian divisive clustering algorithm which integrates summary statistics from genome-wide association studies to detect clusters of colocalised traits from large numbers of traits.

Primary bile acids serve important roles in cholesterol metabolism, lipid digestion, host-microbe interactions, and regulatory pathways in the human host. While most bile acids are reabsorbed and recycled via enterohepatic cycling, ∼5% serve as substrates for bacterial biotransformation in the colon. Enzymes involved in various transformations have been characterized from cultured gut bacteria and reveal taxa-specific distribution. More recently, bioinformatic approaches have revealed greater diversity in isoforms of these enzymes, and the microbial species in which they are found. Thus, the functional roles played by the bile acid-transforming gut microbiota and the distribution of resulting secondary bile acids, in the bile acid pool, may be profoundly affected by microbial community structure and function. Bile acids and the composition of the bile acid pool have historically been hypothesized to be associated with several disease states, including recurrent Clostridium difficile infection, inflammatory bowel diseases, metabolic syndrome, and several cancers. Recently, however, emphasis has been placed on how microbial communities in the dysbiotic gut may alter the bile acid pool to potentially cause or mitigate disease onset. This review highlights the current understanding of the interactions between the gut microbial community, bile acid biotransformation, and disease states, and addresses future directions to better understand these complex associations.

While grazing exclusion is thought to drive soil nutrient transport and cycling, and reduce soil compaction, its direct impact on microbial community composition remains unclear. In this study, we examined the impact of grazing exclusion on abundance and composition of soil microbial (bacterial, archaeal, and fungal) communities, especially those associated with nutrient cycling. We surveyed soil physicochemical properties and litter mass, at sites undergoing varying durations of grazing exclusion (0–34 years) in a semiarid grassland. Using next-generation amplicon sequencing, we further characterized variations in the composition and diversity of soil microbial communities associated with grazing exclusion and soil depths, as well as subsequent changes in physicochemical properties. Most soil physicochemical parameter values significantly increased as the result of long-term grazing exclusion, and these properties were associated with variation in composition and diversity of microbial communities. Notably, the relative abundances of microbial families associated with C cycling (e.g., Chitinophagaceae) increased with an increase in nutrient availability following grazing exclusion. The abundance of the archaeal ammonia-oxidizing Nitrososphaerae increased with decreasing concentration of ammonium among samples. Likewise, fungal communities were also associated with the shifts in nutrient concentrations, although the majority of fungi could not be classified to the species level. Nitrate concentration also played a critical role in shaping bacterial, archaeal, or fungal communities. Moreover, bacterial and archaeal communities had a greater mean Shannon index in 0–10-cm than those in 10–20-cm soil layer. Results of this study provide novel insights regarding how the length of grazing exclusion and soil depth influence nutrient gradients and microbial community composition associated with nutrient cycling.

Fecal microbiota transplantation (FMT) is increasingly being used for treatment of recurrent Clostridium difficile infection (R-CDI) that cannot be cured with antibiotics alone. In addition, FMT is being investigated for a variety of indications where restoration or restructuring of the gut microbial community is hypothesized to be beneficial. We sought to develop a stable, freeze-dried encapsulated preparation of standardized fecal microbiota that can be used for FMT with ease and convenience in clinical practice and research. We systematically developed a lyophilization protocol that preserved the viability of bacteria across the taxonomic spectrum found in fecal microbiota and yielded physicochemical properties that enabled consistent encapsulation. We also treated a cohort of R-CDI patients with a range of doses of encapsulated microbiota and analyzed the associated changes in the fecal microbiome of the recipients. The optimized lyophilized preparation satisfied all our preset goals for physicochemical properties, encapsulation ease, stability at different temperatures, and microbiota viability in vitro and in vivo (germ-free mice). The capsule treatment was administered to 49 patients. Overall, 43/49 (88%) of patients achieved a clinical success, defined as no recurrence of CDI over 2 months. Analysis of the fecal microbiome demonstrated near normalization of the fecal microbial community by 1 month following FMT treatment. The simplest protocol using the lowest dose (2.1-2.5 × 10 bacteria in 2-3 capsules) without any colon purgative performed equally well in terms of clinical outcomes and microbiota engraftment. A single administration of encapsulated, freeze-dried fecal microbiota from a healthy donor was highly successful in treating antibiotic-refractory R-CDI syndrome.