A tiny fraction of all species forms most of nature: Rarity as a sticky state.

Using data from a wide range of natural communities including the human microbiome, plants, fish, mushrooms, rodents, beetles, and trees, we show that universally just a few percent of the species account for most of the biomass. This is in line with the classical observation that the vast bulk of biodiversity is very rare. Attempts to find traits allowing the tiny fraction of abundant species to escape rarity have remained unsuccessful. Here, we argue that this might be explained by the fact that hyper-dominance can emerge through stochastic processes. We demonstrate that in neutrally competing groups of species, rarity tends to become a trap if environmental fluctuations result in gains and losses proportional to abundances. This counter-intuitive phenomenon arises because absolute change tends to zero for very small abundances, causing rarity to become a "sticky state", a pseudoattractor that can be revealed numerically in classical ball-in-cup landscapes. As a result, the vast majority of species spend most of their time in rarity leaving space for just a few others to dominate the neutral community. However, fates remain stochastic. Provided that there is some response diversity, roles occasionally shift as stochastic events or natural enemies bring an abundant species down allowing a rare species to rise to dominance. Microbial time series spanning thousands of generations support this prediction. Our results suggest that near-neutrality within niches may allow numerous rare species to persist in the wings of the dominant ones. Stand-ins may serve as insurance when former key species collapse.

Pre-vaccination immunotypes reveal weak and robust antibody responders to influenza vaccination.

Effective vaccine-induced immune responses are particularly essential in older adults who face an increased risk of immunosenescence. However, the complexity and variability of the human immune system make predicting vaccine responsiveness challenging. To address this knowledge gap, our study aimed to characterize immune profiles that are predictive of vaccine responsiveness using "immunotypes" as an innovative approach. We analyzed an extensive set of innate and adaptive immune cell subsets in the whole blood of 307 individuals (aged 25-92) pre- and post-influenza vaccination which we associated with day 28 hemagglutination inhibition (HI) antibody titers. Building on our previous work that stratified individuals into nine immunotypes based on immune cell subsets, we identified two pre-vaccination immunotypes associated with weak and one showing robust day 28 antibody response. Notably, the weak responders demonstrated HLA-DR+ T-cell signatures, while the robust responders displayed a high naïve-to-memory T-cell ratio and percentage of nonclassical monocytes. These specific signatures deepen our understanding of the relationship between the baseline of the immune system and its functional potential. This approach could enhance our ability to identify individuals at risk of immunosenescence. Our findings highlight the potential of pre-vaccination immunotypes as an innovative tool for informing personalized vaccination strategies and improving health outcomes, particularly for aging populations.

A tool to assess the mock community samples in 16S rRNA gene-based microbiota profiling studies.

Inclusion and investigation of technical controls in microbiome sequencing studies is important for understanding technical biases and errors. Here, we present chkMocks, a general R-based tool that allows researchers to compare the composition of mock communities that are processed along with samples to their theoretical composition. A visual comparison between experimental and theoretical community composition and their correlation is provided for researchers to assess the quality of their sample processing workflows.

Frailty is related to serum inflammageing markers: results from the VITAL study.

Frailty describes an age-associated state in individuals with an increased vulnerability and less resilience against adverse outcomes. To score frailty, studies have employed the questionnaires, such as the SF-36 and EQ-5D-3L, or the Frailty Index, a composite score based on deficit accumulation. Furthermore, ageing of the immune system is often accompanied by a state of low-grade inflammation (inflammageing). Here, we aimed to associate 29 circulating markers of inflammageing with frailty measures in a prospective cohort study to understand the mechanisms underlying ageing.Frailty measures and inflammageing markers were assessed in 317 participants aged 25-90. We determined four different measures of frailty: the Frailty Index based on 31 deficits, the EQ-5D-3L and two physical domains of the SF-36. Serum/plasma levels of inflammageing markers and CMV/EBV seropositivity were measured using different techniques: Quanterix, Luminex or ELISA.All four measures of frailty strongly correlated with age and BMI. Nineteen biomarkers correlated with age, some in a linear fashion (IL-6, YKL-40), some only in the oldest age brackets (CRP), and some increased at younger ages and then plateaued (CCL2, sIL-6R). After correcting for age, biomarkers, such as IL-6, CRP, IL-1RA, YKL-40 and elastase, were associated with frailty. When corrected for BMI, the number of associations reduced further.In conclusion, inflammageing markers, particularly markers reflecting innate immune activation, are related to frailty. These findings indicate that health decline and the accumulation of deficits with age is accompanied with a low-grade inflammation which can be detected by specific inflammatory markers.

Unveiling and harnessing the human gut microbiome in the rising burden of non-communicable diseases during urbanization.

The world is witnessing a global increase in the urban population, particularly in developing Asian and African countries. Concomitantly, the global burden of non-communicable diseases (NCDs) is rising, markedly associated with the changing landscape of lifestyle and environment during urbanization. Accumulating studies have revealed the role of the gut microbiome in regulating the immune and metabolic homeostasis of the host, which potentially bridges external factors to the host (patho-)physiology. In this review, we discuss the rising incidences of NCDs during urbanization and their links to the compositional and functional dysbiosis of the gut microbiome. In particular, we elucidate the effects of urbanization-associated factors (hygiene/pollution, urbanized diet, lifestyles, the use of antibiotics, and early life exposure) on the gut microbiome underlying the pathogenesis of NCDs. We also discuss the potential and feasibility of microbiome-inspired and microbiome-targeted approaches as novel avenues to counteract NCDs, including fecal microbiota transplantation, diet modulation, probiotics, postbiotics, synbiotics, celobiotics, and precision antibiotics.

Wavelet clustering analysis as a tool for characterizing community structure in the human microbiome.

Human microbiome research is helped by the characterization of microbial networks, as these may reveal key microbes that can be targeted for beneficial health effects. Prevailing methods of microbial network characterization are based on measures of association, often applied to limited sampling points in time. Here, we demonstrate the potential of wavelet clustering, a technique that clusters time series based on similarities in their spectral characteristics. We illustrate this technique with synthetic time series and apply wavelet clustering to densely sampled human gut microbiome time series. We compare our results with hierarchical clustering based on temporal correlations in abundance, within and across individuals, and show that the cluster trees obtained by using either method are significantly different in terms of elements clustered together, branching structure and total branch length. By capitalizing on the dynamic nature of the human microbiome, wavelet clustering reveals community structures that remain obscured in correlation-based methods.

Reducing bias in microbiome research: Comparing methods from sample collection to sequencing.

Background: Microbiota profiles are strongly influenced by many technical aspects that impact the ability of researchers to compare results. To investigate and identify potential biases introduced by technical variations, we compared several approaches throughout the entire workflow of a microbiome study, from sample collection to sequencing, using commercially available mock communities (from bacterial strains as well as from DNA) and multiple human fecal samples, including a large set of positive controls created as a random mix of several participant samples. Methods: Human fecal material was sampled, and aliquots were used to test two commercially available stabilization solutions (OMNIgene·GUT and Zymo Research) in comparison to samples frozen immediately upon collection. In addition, the methodology for DNA extraction, input of DNA, or the number of PCR cycles were analyzed. Furthermore, to investigate the potential batch effects in DNA extraction, sequencing, and barcoding, we included 139 positive controls. Results: Samples preserved in both the stabilization buffers limited the overgrowth of Enterobacteriaceae when compared to unpreserved samples stored at room temperature (RT). These stabilized samples stored at RT were different from immediately frozen samples, where the relative abundance of Bacteroidota was higher and Actinobacteriota and Firmicutes were lower. As reported previously, the method used for cell disruption was a major contributor to variation in microbiota composition. In addition, a high number of cycles during PCR lead to an increase in contaminants detected in the negative controls. The DNA extraction had a significant impact on the microbial composition, also observed with the use of different Illumina barcodes during library preparation and sequencing, while no batch effect was observed in replicate runs. Conclusion: Our study reaffirms the importance of the mechanical cell disruption method and immediate frozen storage as critical aspects in fecal microbiota studies. A comparison of storage conditions revealed that the bias was limited in RT samples preserved in stabilization systems, and these may be a suitable compromise when logistics are challenging due to the size or location of a study. Moreover, to reduce the effect of contaminants in fecal microbiota profiling studies, we suggest the use of ~125 pg input DNA and 25 PCR cycles as optimal parameters during library preparation.

Species-Specific Patterns of Gut Metabolic Modules in Dutch Individuals with Different Dietary Habits.

Diet is an important determinant of the human gut microbiome. Here, we analyzed fecal metagenomes of Dutch adults following omnivorous, pescatarian, vegan, and vegetarian diets. We compared the taxonomic composition of individuals from our study with publicly available gut metagenomes from westernized and non-westernized societies. We observed that, despite long-term transition to diets rich in plant fibers (vegan or vegetarian), the microbiomes of these were typical of westernized populations, and similar in composition to omnivores. Although there were no major differences in metabolic modules, we identified differences in the species that contributed to particular functions, such as carbohydrate degradation and short-chain fatty acid metabolism. Overall, this study shows functional redundancy of the microbiomes among westernized populations, which is independent of long-term individual dietary habits. IMPORTANCE Diet is an important modulator of the human gut microbiome, which is susceptible to increased consumption of plant fibers in vegan or vegetarian lifestyles. To investigate this, we compared the gut microbiome of Dutch adults following omnivorous, pescatarian, vegan and vegetarian diets. We did not observe major differences in the gut microbiome composition and function between individuals with different dietary habits. However, we observed differences in the species that contribute to the core functions of the gut microbiome. Our study thus emphasizes the need to better understand the species-specific functional changes associated with dietary habits in the human gut microbiome.

Identification of aging-associated immunotypes and immune stability as indicators of post-vaccination immune activation.

Immunosenescence describes immune dysfunction observed in older individuals. To identify individuals at-risk for immune dysfunction, it is crucial to understand the diverse immune phenotypes and their intrinsic functional capabilities. We investigated immune cell subsets and variation in the aging population. We observed that inter-individual immune variation was associated with age and cytomegalovirus seropositivity. Based on the similarities of immune subset composition among individuals, we identified nine immunotypes that displayed different aging-associated immune signatures, which explained inter-individual variation better than age. Additionally, we correlated the immune subset composition of individuals over approximately a year as a measure of stability of immune parameters. Immune stability was significantly lower in immunotypes that contained aging-associated immune subsets and correlated with a circulating CD38 + CD4+ T follicular helper cell increase 7 days after influenza vaccination. In conclusion, immune stability is a feature of immunotypes and could be a potential indicator of post-vaccination cellular kinetics.

An in vitro fermentation model to study the impact of bacteriophages targeting Shiga toxin-encoding Escherichia coli on the colonic microbiota.

Lytic bacteriophages are considered safe for human consumption as biocontrol agents against foodborne pathogens, in particular in ready-to-eat foodstuffs. Phages could, however, evolve to infect different hosts when passing through the gastrointestinal tract (GIT). This underlines the importance of understanding the impact of phages towards colonic microbiota, particularly towards bacterial families usually found in the colon such as the Enterobacteriaceae. Here we propose in vitro batch fermentation as model for initial safety screening of lytic phages targeting Shiga toxin-producing Escherichia coli (STEC). As inoculum we used faecal material of three healthy donors. To assess phage safety, we monitored fermentation parameters, including short chain fatty acid production and gas production/intake by colonic microbiota. We performed shotgun metagenomic analysis to evaluate the outcome of phage interference with colonic microbiota composition and functional potential. During the 24 h incubation, concentrations of phage and its host were also evaluated. We found the phage used in this study, named E. coli phage vB_EcoS_Ace (Ace), to be safe towards human colonic microbiota, independently of the donors' faecal content used. This suggests that individuality of donor faecal microbiota did not interfere with phage effect on the fermentations. However, the model revealed that the attenuated STEC strain used as phage host perturbed the faecal microbiota as based on metagenomic analysis, with potential differences in metabolic output. We conclude that the in vitro batch fermentation model used in this study is a reliable safety screening for lytic phages intended to be used as biocontrol agents.

Dynamic metabolic interactions and trophic roles of human gut microbes identified using a minimal microbiome exhibiting ecological properties.

Microbe-microbe interactions in the human gut are influenced by host-derived glycans and diet. The high complexity of the gut microbiome poses a major challenge for unraveling the metabolic interactions and trophic roles of key microbes. Synthetic minimal microbiomes provide a pragmatic approach to investigate their ecology including metabolic interactions. Here, we rationally designed a synthetic microbiome termed Mucin and Diet based Minimal Microbiome (MDb-MM) by taking into account known physiological features of 16 key bacteria. We combined 16S rRNA gene-based composition analysis, metabolite measurements and metatranscriptomics to investigate community dynamics, stability, inter-species metabolic interactions and their trophic roles. The 16 species co-existed in the in vitro gut ecosystems containing a mixture of complex substrates representing dietary fibers and mucin. The triplicate MDb-MM's followed the Taylor's power law and exhibited strikingly similar ecological and metabolic patterns. The MDb-MM exhibited resistance and resilience to temporal perturbations as evidenced by the abundance and metabolic end products. Microbe-specific temporal dynamics in transcriptional niche overlap and trophic interaction network explained the observed co-existence in a competitive minimal microbiome. Overall, the present study provides crucial insights into the co-existence, metabolic niches and trophic roles of key intestinal microbes in a highly dynamic and competitive in vitro ecosystem.

Inter-species Metabolic Interactions in an In-vitro Minimal Human Gut Microbiome of Core Bacteria.

Knowledge of the functional roles and interspecies interactions are crucial for improving our understanding of the human intestinal microbiome in health and disease. However, the complexity of the human intestinal microbiome and technical challenges in investigating it pose major challenges. In this proof-of-concept study, we rationally designed, assembled and experimentally tested a synthetic Diet-based Minimal Microbiome (Db-MM) consisting of ten core intestinal bacterial species that together are capable of efficiently converting dietary fibres into short chain fatty acids (SCFAs). Despite their genomic potential for metabolic competition, all ten bacteria coexisted during growth on a mixture of dietary fibres, including pectin, inulin, xylan, cellobiose and starch. By integrated analyses of metabolite production, community composition and metatranscriptomics-based gene expression data, we identified interspecies metabolic interactions leading to production of key SCFAs such as butyrate and propionate. While public goods, such as sugars liberated from colonic fibres, are harvested by non-degraders, some species thrive by cross-feeding on energetically challenging substrates, including the butyrogenic conversion of acetate and lactate. Using a reductionist approach in an in-vitro system combined with functional measurements, our study provides key insights into the complex interspecies metabolic interactions between core intestinal bacterial species.

Associations and recovery dynamics of the nasopharyngeal microbiota during influenza-like illness in the aging population.

Influenza-like illness (ILI), a disease caused by respiratory pathogens including influenza virus, is a major health concern in older adults. There is little information on changes and recovery dynamics of the nasopharyngeal (NP) microbiota of older adults associated with an ILI. Here, we compared the NP microbiota in older adults reporting (n = 240) or not (n = 157) ILI during the 2014-2015 influenza season at different times of the ILI event. A small but significant effect of the ILI was observed on the microbiota community composition and structure when compared to controls and samples collected at recovery. Corynebacterium was negatively associated with ILI and its abundance increased after recovery. Potential pathobionts such as Haemophilus, Porphyromonas and Gemella had higher abundances during acute-ILI. Stability and changes in the NP microbial community showed individual dynamics. Key core genera, Corynebacterium, Moraxella and Dolosigranulum exhibited higher inter-individual variability in acute-ILI, but showed comparable variability to controls after recovery. Participants in the ILI group with higher core microbiota abundances at the acute phase showed higher microbiota stability after recovery. Our findings demonstrate that acute-ILI is associated with alterations in the phylogenetic structure of the NP microbiota in older adults. The variation in the core microbiota suggests imbalances in the ecosystem, which could potentially play a role in the susceptibility and recovery of the NP microbiota after an ILI event.

Impact of long-term dietary habits on the human gut resistome in the Dutch population.

The human gut microbiome plays a central role in health and disease. Environmental factors, such as lifestyle and diet, are known to shape the gut microbiome as well as the reservoir of resistance genes that these microbes harbour; the resistome. In this study we assessed whether long-term dietary habits within a single geographical region (the Netherlands) impact the human gut resistome. Faecal samples from Dutch omnivores, pescatarians, vegetarians and vegans were analysed by metagenomic shotgun sequencing (MSS) (n = 149) and resistome capture sequencing approach (ResCap) (n = 64). Among all diet groups, 119 and 145 unique antibiotic resistance genes (ARGs) were detected by MSS or ResCap, respectively. Five or fifteen ARGs were shared between all diet groups, based on MSS and ResCap, respectively. The total number of detected ARGs by MSS or ResCap was not significantly different between the groups. MSS also revealed that vegans have a distinct microbiome composition, compared to other diet groups. Vegans had a lower abundance of Streptococcus thermophilus and Lactococcus lactis compared to pescatarians and a lower abundance of S. thermophilus when compared to omnivores. In summary, our study showed that long-term dietary habits are not associated with a specific resistome signature.

Modulation of human intestinal microbiota in a clinical trial by consumption of a ß-D-glucan-enriched extract obtained from Lentinula edodes.

PURPOSE: The aim of this study was to evaluate the hypocholesterolemic, immune- and microbiota-modulatory effect of a mushroom extract in hypercholesterolemic subjects. METHODS: A randomized, controlled, double-blind, and parallel clinical trial was carried out with subjects from 18 to 65 years old (n = 52) with untreated mild hypercholesterolemia. Volunteers consumed a ß-D-glucan-enriched (BGE) mixture (10.4 g/day) obtained from shiitake mushrooms (Lentinula edodes) ensuring a 3.5 g/day of fungal ß-D-glucans or a placebo incorporated in three different commercial creams. RESULTS: This mixture showed hypocholesterolemic activities in vitro and in animal studies. After eight weeks intervention, no significant differences in lipid- or cholesterol-related parameters were found compared to placebo subjects as well as before and after the BGE mixture administration. No inflammatory or immunomodulatory responses were noticed and no changes in IL-1ß, IL-6, TNF-α or oxLDL were recorded. However, consumption of the BGE mixture was safe and managed to achieve the dietary fibre intake recommended as cardiovascular protective diet. Moreover, the BGE mixture modulated the colonic microbiota differently compared to placebo. Microbial community composition varied from before to after the intervention with several genera being positively or negatively correlated with some biomarkers related to cholesterol metabolism. CONCLUSION: These results suggested a relation between cholesterol metabolism, microbiota and BGE administration. Nevertheless, the precise significance of this differential modulation was not fully elucidated and requires further studies.

Unravelling lactate-acetate and sugar conversion into butyrate by intestinal Anaerobutyricum and Anaerostipes species by comparative proteogenomics.

The d- and l-forms of lactate are important fermentation metabolites produced by intestinal bacteria but are found to negatively affect mucosal barrier function and human health. Both enantiomers of lactate can be converted with acetate into the presumed beneficial butyrate by a phylogenetically related group of anaerobes, including Anaerobutyricum and Anaerostipes spp. This is a low energy yielding process with a partially unknown pathway in Anaerobutyricum and Anaerostipes spp. and hence, we sought to address this via a comparative genomics, proteomics and physiology approach. We compared growth of Anaerobutyricum soehngenii on lactate with that on sucrose and sorbitol. Comparative proteomics revealed complete pathway of butyrate formation from sucrose, sorbitol and lactate. Notably, a gene cluster, lctABCDEF was abundantly expressed when grown on lactate. This gene cluster encodes a lactate dehydrogenase (lctD), electron transport proteins A and B (lctCB), nickel-dependent racemase (lctE), lactate permease (lctF) and short-chain acyl-CoA dehydrogenase (lctG). Investigation of available genomes of intestinal bacteria revealed this new gene cluster to be highly conserved in only Anaerobutyricum and Anaerostipes spp. Present study demonstrates that A. soehngenii and several related Anaerobutyricum and Anaerostipes spp. are highly adapted for a lifestyle involving lactate plus acetate utilization in the human intestinal tract.

Biosulfidogenesis Mediates Natural Attenuation in Acidic Mine Pit Lakes.

Acidic pit lakes are abandoned open pit mines filled with acid mine drainage (AMD)-highly acidic, metalliferous waters that pose a severe threat to the environment and are rarely properly remediated. Here, we investigated two meromictic, oligotrophic acidic mine pit lakes in the Iberian Pyrite Belt (IPB), Filón Centro (Tharsis) (FC) and La Zarza (LZ). We observed a natural attenuation of acidity and toxic metal concentrations towards the lake bottom, which was more pronounced in FC. The detection of Cu and Zn sulfides in the monimolimnion of FC suggests precipitation of dissolved metals as metal sulfides, pointing to biogenic sulfide formation. This was supported by microbial diversity analysis via 16S rRNA gene amplicon sequencing of samples from the water column, which showed the presence of sulfidogenic microbial taxa in FC and LZ. In the monimolimnion of FC, sequences affiliated with the putative sulfate-reducing genus Desulfomonile were dominant (58%), whereas in the more acidic and metal-enriched LZ, elemental sulfur-reducing Acidianus and Thermoplasma spp., and disproportionating Desulfocapsa spp. were more abundant. Furthermore, the detection of reads classified as methanogens and Desulfosporosinus spp., although at low relative abundance, represents one of the lowest pH values (2.9 in LZ) at which these taxa have been reported, to our knowledge. Analysis of potential biomarker lipids provided evidence that high levels of phosphocholine lipids with mixed acyl/ether glycerol core structures were associated with Desulfomonile, while ceramide lipids were characteristic of Microbacter in these environments. We propose that FC and LZ function as natural bioremediation reactors where metal sulfide precipitation is mediated by biosulfidogenesis starting from elemental sulfur reduction and disproportionation at an early stage (LZ), followed by sulfate reduction at a later stage (FC).

Metagenomic Analysis of Regularly Microwave-Treated and Untreated Domestic Kitchen Sponges.

Kitchen sponges massively absorb and spread microorganisms, leading to contamination of kitchen appliances, surfaces, and food. Microwaving as an effective and widespread technique can rapidly reduce the microbial load of kitchen sponges. However, long-term effects of such treatments are largely unknown. Notably, it has been speculated that regularly applied domestic cleaning and disinfection may select for microbial communities with a higher pathogenic potential and/or malodorous properties. In this study, we distributed newly purchased polyurethane kitchen sponges to 20 participants, with the instruction to use them under normal household conditions for four weeks. Ten of the participants sanitized their sponges regularly by a standardized microwaving protocol, while the remaining ten sponges remained untreated. Metagenomic sequence data evaluation indicated that, in addition to bacteria, viruses, eukaryotes, and archaea were also part of the kitchen sponge microbiome. Comparisons of sanitized and untreated kitchen sponges indicated a trend towards a reduced structural microbial diversity while functional diversity increased. Microwave sanitization appeared to alter composition and metabolic properties of the microbial communities. Follow-up studies will have to show whether these changes are more positive or negative in terms of domestic hygiene, human health, and well-being.

Metagenomic- and Cultivation-Based Exploration of Anaerobic Chloroform Biotransformation in Hypersaline Sediments as Natural Source of Chloromethanes.

Chloroform (CF) is an environmental contaminant that can be naturally formed in various environments ranging from forest soils to salt lakes. Here we investigated CF removal potential in sediments obtained from hypersaline lakes in Western Australia. Reductive dechlorination of CF to dichloromethane (DCM) was observed in enrichment cultures derived from sediments of Lake Strawbridge, which has been reported as a natural source of CF. No CF removal was observed in abiotic control cultures without artificial electron donors, indicating biotic CF dechlorination in the enrichment cultures. Increasing vitamin B12 concentration from 0.04 to 4 µM in enrichment cultures enhanced CF removal and reduced DCM formation. In cultures amended with 4 µM vitamin B12 and 13C labelled CF, formation of 13CO2 was detected. Known organohalide-respiring bacteria and reductive dehalogenase genes were neither detected using quantitative PCR nor metagenomic analysis of the enrichment cultures. Rather, members of the order Clostridiales, known to co-metabolically transform CF to DCM and CO2, were detected. Accordingly, metagenome-assembled genomes of Clostridiales encoded enzymatic repertoires for the Wood-Ljungdahl pathway and cobalamin biosynthesis, which are known to be involved in fortuitous and nonspecific CF transformation. This study indicates that hypersaline lake microbiomes may act as a filter to reduce CF emission to the atmosphere.