Storage and handling of human faecal samples affect the gut microbiome composition: A feasibility study

High-throughput DNA extraction strategy for fecal microbiome studies

Microbiome studies are becoming larger in size to detect the potentially small effect that environmental factors have on our gut microbiomes, or that the microbiome has on our health. Therefore, fast and reproducible DNA isolation methods are needed to handle thousands of fecal samples. We used the Chemagic 360 chemistry and Magnetic Separation Module I (MSMI) instrument to compare two sample preservatives and four different pre-treatment protocols to find an optimal method for DNA isolation from thousands of fecal samples. The pre-treatments included bead beating, sample handling in tube and plate format, and proteinase K incubation. The optimal method offers a sufficient yield of high-quality DNA without contamination. Three human fecal samples (adult, senior, and infant) with technical replicates were extracted. The extraction included negative controls (OMNIgeneGUT, DNA/RNA shield fluid, and Chemagic Lysis Buffer 1) to detect cross-contamination and ZymoBIOMICS Gut Microbiome Standard as a positive control to mimic the human gut microbiome and assess sensitivity of the extraction method. All samples were extracted using Chemagic DNA Stool 200 H96 kit (PerkinElmer, Finland). The samples were collected in two preservatives, OMNIgeneGUT and DNA/RNA shield fluid. DNA quantity was measured using Qubit-fluorometer, DNA purity and quality using gel electrophoresis, and taxonomic signatures with 16S rRNA gene-based sequencing with V3V4 and V4 regions. Bead beating increased bacterial diversity. The largest increase was detected in gram-positive genera Blautia, Bifidobacterium, and Ruminococcus. Preservatives showed minor differences in bacterial abundances. The profiles between the V3V4 and V4 regions differed considerably with lower diversity samples. Negative controls showed signs from genera abundant in fecal samples. Technical replicates of the Gut Standard and stool samples showed low variation. The selected isolation protocol included recommended steps from manufacturer as well as bead beating. Bead beating was found to be necessary to detect hard-to-lyse bacteria. The protocol was reproducible in terms of DNA yield among different stool replicates and the ZymoBIOMICS Gut Microbiome Standard. The MSM1 instrument and pre-treatment in a 96-format offered the possibility of automation and handling of large sample collections. Both preservatives were feasible in terms of sample handling and had low variation in taxonomic signatures. The 16S rRNA target region had a high impact on the composition of the bacterial profile.

IMPORTANCE

Next-generation sequencing (NGS) is a widely used method for determining the composition of the gut microbiota. Due to the differences in the gut microbiota composition between individuals, microbiome studies have expanded into large population studies to maximize detection of small effects on microbe-host interactions. Thus, the demand for a rapid and reliable microbial profiling is continuously increasing, making the optimization of high-throughput 96-format DNA extraction integral for NGS-based downstream applications. However, experimental protocols are prone to bias and errors from sample collection and storage, to DNA extraction, primer selection and sequencing, and bioinformatics analyses. Methodological bias can contribute to differences in microbiome profiles, causing variability across studies and laboratories using different protocols. To improve consistency and confidence of the measurements, the standardization of microbiome analysis methods has been recognized in many fields.

Gut bacteriome and mood disorders in women with PCOS

STUDY QUESTION

How does the gut bacteriome differ based on mood disorders (MDs) in women with polycystic ovary syndrome (PCOS), and how can the gut bacteriome contribute to the associations between these two conditions?

SUMMARY ANSWER

Women with PCOS who also have MDs exhibited a distinct gut bacteriome with reduced alpha diversity and a significantly lower abundance of Butyricicoccus compared to women with PCOS but without MDs.

WHAT IS KNOWN ALREADY

Women with PCOS have a 4- to 5-fold higher risk of having MDs compared to women without PCOS. The gut bacteriome has been suggested to influence the pathophysiology of both PCOS and MDs.

STUDY DESIGN, SIZE, DURATION

This population-based cohort study was derived from the Northern Finland Birth Cohort 1966 (NFBC1966), which includes all women born in Northern Finland in 1966. Women with PCOS who donated a stool sample at age 46 years (n = 102) and two BMI-matched controls for each case (n = 205), who also responded properly to the MD criteria scales, were included.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A total of 102 women with PCOS and 205 age- and BMI-matched women without PCOS were included. Based on the validated MD criteria, the subjects were categorized into MD or no-MD groups, resulting in the following subgroups: PCOS no-MD (n = 84), PCOS MD (n = 18), control no-MD (n = 180), and control MD (n = 25). Clinical characteristics were assessed at age 31 years and age 46 years, and stool samples were collected from the women at age 46 years, followed by the gut bacteriome analysis using 16 s rRNA sequencing. Alpha diversity was assessed using observed features and Shannon's index, with a focus on genera, and beta diversity was characterized using principal components analysis (PCA) with Bray-Curtis Dissimilarity at the genus level. Associations between the gut bacteriome and PCOS-related clinical features were explored by Spearman's correlation coefficient. A P-value for multiple testing was adjusted with the Benjamini-Hochberg false discovery rate (FDR) method.

MAIN RESULTS AND THE ROLE OF CHANCE

We observed changes in the gut bacteriome associated with MDs, irrespective of whether the women also had PCOS. Similarly, PCOS MD cases showed a lower alpha diversity (Observed feature, PCOS no-MD, median 272; PCOS MD, median 208, FDR = 0.01; Shannon, PCOS no-MD, median 5.95; PCOS MD, median 5.57, FDR = 0.01) but also a lower abundance of Butyricicoccus (log-fold changeAnalysis of Compositions of Microbiomes with Bias Correction (ANCOM-BC)=-0.90, FDRANCOM-BC=0.04) compared to PCOS no-MD cases. In contrast, in the controls, the gut bacteriome did not differ based on MDs. Furthermore, in the PCOS group, Sutterella showed positive correlations with PCOS-related clinical parameters linked to obesity (BMI, r2=0.31, FDR = 0.01; waist circumference, r2=0.29, FDR = 0.02), glucose metabolism (fasting glucose, r2=0.46, FDR < 0.001; fasting insulin, r2=0.24, FDR = 0.05), and gut barrier integrity (zonulin, r2=0.25, FDR = 0.03).

LIMITATIONS, REASONS FOR CAUTION

Although this was the first study to assess the link between the gut bacteriome and MDs in PCOS and included the largest PCOS dataset for the gut microbiome analysis, the number of subjects stratified by the presence of MDs was limited when contrasted with previous studies that focused on MDs in a non-selected population.

WIDER IMPLICATIONS OF THE FINDINGS

The main finding is that gut bacteriome is associated with MDs irrespective of the PCOS status, but PCOS may also modulate further the connection between the gut bacteriome and MDs.

STUDY FUNDING/COMPETING INTEREST(S)

This research was funded by the European Union's Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant Agreement (MATER, No. 813707), the Academy of Finland (project grants 315921, 321763, 336449), the Sigrid Jusélius Foundation, Novo Nordisk Foundation (NNF21OC0070372), grant numbers PID2021-12728OB-100 (Endo-Map) and CNS2022-135999 (ROSY) funded by MCIN/AEI/10.13039/501100011033 and ERFD A Way of Making Europe. The study was also supported by EU QLG1-CT-2000-01643 (EUROBLCS) (E51560), NorFA (731, 20056, 30167), USA/NIH 2000 G DF682 (50945), the Estonian Research Council (PRG1076, PRG1414), EMBO Installation (3573), and Horizon 2020 Innovation Grant (ERIN, No. EU952516). The funders did not participate in any process of the study. We have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Interaction of microbiota, mucosal malignancies, and immunotherapy-Mechanistic insights

The microbiome has emerged as a crucial modulator of host-immune interactions and clearly impacts tumor development and therapy efficacy. The microbiome is a double-edged sword in cancer development and therapy as both pro-tumorigenic and anti-tumorigenic bacterial taxa have been identified. The staggering number of association-based studies in various tumor types has led to an enormous amount of data that makes it difficult to identify bacteria that promote tumor development or modulate therapy efficacy from bystander bacteria. Here we aim to comprehensively summarize the current knowledge of microbiome-host immunity interactions and cancer therapy in various mucosal tissues to find commonalities and thus identify potential functionally relevant bacterial taxa. Moreover, we also review recent studies identifying specific bacteria and mechanisms through which the microbiome modulates cancer development and therapy efficacy.

Documenting the diversity of the Namibian Ju|'hoansi intestinal microbiome

We investigate the bacterial and fungal composition and functionality of the Ju|'hoansi intestinal microbiome (IM). The Juǀ'hoansi are a hunter-gatherer community residing in northeastern Namibia. They formerly subsisted by hunting and gathering but have been increasingly exposed to industrial dietary sources, medicines, and lifestyle features. They present an opportunity to study the evolution of the human IM in situ, from a predominantly hunter-gatherer to an increasingly Western urban-forager-farmer lifestyle. Their bacterial IM resembles that of typical hunter-gatherers, being enriched for genera such as Prevotella, Blautia, Faecalibacterium, Succinivibrio, and Treponema. Fungal IM inhabitants include animal pathogens and plant saprotrophs such as Fusarium, Issatchenkia, and Panellus. Our results suggest that diet and culture exert a greater influence on Ju|'hoansi IM composition than age, self-identified biological sex, and medical history. The Ju|'hoansi exhibit a unique core IM composition that diverges from the core IMs of other populations.

Exploring the gut microbiota: lifestyle choices, disease associations, and personal genomics

The gut microbiota is a rich and dynamic ecosystem that actively interacts with the human body, playing a significant role in the state of health and disease of the host. Diet, exercise, mental health, and other factors have exhibited the ability to influence the gut bacterial composition, leading to changes that can prevent and improve, or favor and worsen, both intestinal and extra-intestinal conditions. Altered gut microbial states, or 'dysbiosis', associated with conditions and diseases are often characterized by shifts in bacterial abundance and diversity, including an impaired Firmicutes to Bacteroidetes ratio. By understanding the effect of lifestyle on the gut microbiota, personalized advice can be generated to suit each individual profile and foster the adoption of lifestyle changes that can both prevent and ameliorate dysbiosis. The delivery of effective and reliable advice, however, depends not only on the available research and current understanding of the topic, but also on the methods used to assess individuals and to discover the associations, which can introduce bias at multiple stages. The aim of this review is to summarize how human gut microbial variability is defined and what lifestyle choices and diseases have shown association with gut bacterial composition. Furthermore, popular methods to investigate the human gut microbiota are outlined, with a focus on the possible bias caused by the lack of use of standardized methods. Finally, an overview of the current state of personalized advice based on gut microbiota testing is presented, underlining its power and limitations.

Effects of Stool Sample Preservation Methods on Gut Microbiota Biodiversity: New Original Data and Systematic Review with Meta-Analysis

Here, we aimed to compare the effects of different preservation methods on outcomes of fecal microbiota. We evaluated the effects of different preservation methods using stool sample preservation experiments for up to 1 year. The stool samples from feces of healthy volunteers were grouped based on whether absolute ethanol was added and whether they were hypothermically preserved. Besides, we performed a systematic review to combine current fecal microbiota preservation evidence. We found that Proteobacteria changed significantly and Veillonellaceae decreased significantly in the 12th month in the room temperature + absolute ethanol group. The four cryopreservation groups have more similarities with fresh sample in the 12 months; however, different cryopreservation methods have different effects on several phyla, families, and genera. A systematic review showed that the Shannon diversity and Simpson index of samples stored in RNAlater for 1 month were not statistically significant compared with those stored immediately at -80°C (P = 0.220 and P = 0.123, respectively). The -80°C refrigerator and liquid nitrogen cryopreservation with 10% glycerine can both maintain stable microbiota of stool samples for long-term preservation. The addition of absolute ethanol to cryopreserved samples had no significant difference in the effect of preserving fecal microbial characteristics. Our study provides empirical insights into preservation details for future studies of the long-term preservation of fecal microbiota. Systematic review and meta-analysis found that the gut microbiota structure, composition, and diversity of samples preserved by storage methods, such as preservation solution, are relatively stable, which were suitable for short-term storage at room temperature. IMPORTANCE The study of gut bacteria has become increasingly popular, and fecal sample preservation methods and times need to be standardized. Here, we detail a 12-month study of fecal sample preservation, and our study provides an empirical reference about experimental details for long-term high-quality storage of fecal samples in the field of gut microbiology research. The results showed that the combination of -80°C/liquid nitrogen deep cryopreservation and 10% glycerol was the most effective method for the preservation of stool samples, which is suitable for long-term storage for at least 12 months. The addition of anhydrous ethanol to the deep cryopreserved samples did not make a significant difference in the preservation of fecal microbiological characteristics. Combined with the results of systematic reviews and meta-analyses, we believe that, when researchers preserve fecal specimens, it is essential to select the proper preservation method and time period in accordance with the goal of the study.

Comparison of four DNA extraction kits efficiency for 16SrDNA microbiota profiling of diverse human samples

Aim: The current study investigated the performance of 4 widely used DNA extraction kits using different types of high (stool) and low biomass samples (chyme, broncho alveolar lavage and sputum). Methods: Qiagen Powerfecal Pro DNA kit, Macherey Nucleospin Soil kit, Macherey Nucleospin Tissue Kit and MagnaPure LC DNA isolation kit III were evaluated in terms of DNA quantity, quality, diversity and composition profiles. Results: The quantity and quality of DNA varied among the four kits. The microbiota of the stool samples showed similar diversity and compositional profiles for the 4 kits. Conclusion: Despite differences in DNA quality and quantity, the 4 kits yielded similar results for stool samples, while all kits were not sensitive enough for low biomass samples.

Microbiome-Based Stain Analyses in Crime Scenes

Recent advances in next-generation sequencing technologies (NGS) coupled with machine learning have demonstrated the potential of microbiome-based analyses in applied areas such as clinical diagnostics and forensic sciences. Particularly in forensics, microbial markers in biological stains left at a crime scene can provide valuable information for the reconstruction of crime scene cases, as they contain information on bodily origin, the time since deposition, and donor(s) of the stain. Importantly, microbiome-based analyses provide a complementary or an alternative approach to current methods when these are limited or not feasible. Despite the promising results from recent research, microbiome-based stain analyses are not yet employed in routine casework. In this review, we highlight the two main gaps that need to be addressed before we can successfully integrate microbiome-based analyses in applied areas with a special focus on forensic casework: one is a comprehensive assessment of the method's strengths and limitations, and the other is the establishment of a standard operating procedure. For the latter, we provide a roadmap highlighting key decision steps and offering laboratory and bioinformatic workflow recommendations, while also delineating those aspects that require further testing. Our goal is to ultimately facilitate the streamlining of microbiome-based analyses within the existing forensic framework to provide alternate lines of evidence, thereby improving the quality of investigations.

Individuality and stability of the koala (Phascolarctos cinereus) faecal microbiota through time

Gut microbiota studies often rely on a single sample taken per individual, representing a snapshot in time. However, we know that gut microbiota composition in many animals exhibits intra-individual variation over the course of days to months. Such temporal variations can be a confounding factor in studies seeking to compare the gut microbiota of different wild populations, or to assess the impact of medical/veterinary interventions. To date, little is known about the variability of the koala (Phascolarctos cinereus) gut microbiota through time. Here, we characterise the gut microbiota from faecal samples collected at eight timepoints over a month for a captive population of South Australian koalas (n individuals = 7), and monthly over 7 months for a wild population of New South Wales koalas (n individuals = 5). Using 16S rRNA gene sequencing, we found that microbial diversity was stable over the course of days to months. Each koala had a distinct faecal microbiota composition which in the captive koalas was stable across days. The wild koalas showed more variation across months, although each individual still maintained a distinct microbial composition. Per koala, an average of 57 (±16) amplicon sequence variants (ASVs) were detected across all time points; these ASVs accounted for an average of 97% (±1.9%) of the faecal microbial community per koala. The koala faecal microbiota exhibits stability over the course of days to months. Such knowledge will be useful for future studies comparing koala populations and developing microbiota interventions for this regionally endangered marsupial.

A simplified protocol for DNA extraction from FTA cards for faecal microbiome studies

As metagenomic studies continue to increase in size and complexity, they are often required to incorporate data from geographically isolated locations or longitudinal time samples. This represents a technical challenge, given that many of the commonly used methods used for sample collection, storage, and DNA extraction are sensitive to differences related to the time, storage and chemistry involved. FTA cards have been previously proposed as a simple, reliable and cost-efficient method for the preservation of animal faecal microbiomes. In this study, we report a simplified extraction methodology for recovering microbiome DNA from faeces stored on FTA cards and compare its performance to a common alternative means of characterising such microbiomes; namely, immediate freezing of the faeces followed by DNA extraction using the Qiagen PowerSoil DNA isolation kit. Our results show that overall the application of our simplified DNA extraction methodology yields microbial community results that have higher diversity and an expanded core microbiome than that found using the PowerSoil methodology. This suggests that the FTA card extraction method presented here is a viable alternative for metagenomic studies using faecal material when traditional freeze-based storage methods are not feasible.

Storage of soil microbiome for application in sustainable agriculture: prospects and challenges

Soil microbiome is a dynamic micro-ecosystem driving and fine-tuning several biological processes in the global macro-ecosystems. Its tremendous potential towards mediating sustainability in the ecosystem necessitates the urgent need to store it optimally and efficiently as "next-generation biologicals" for future applications via soil transplantation. The challenge, therefore, is to devise a strategy for the storage of soil microbiome such that its "functionality" is preserved for later application. This review discusses the current endeavours made towards storage of the soil microbiome. The methods for assessing the integrity of soil microbiome by targeting the structural diversity and functional potential of the preserved microbiomes have also been discussed. Further, the success stories related to the storage of fecal microbiome for application in transplants have also been highlighted. This is done primarily with the objective of learning lessons, and parallel application of the knowledge gained, in bringing about improvement in the research domain of soil microbiome storage. Subsequently, the limitations of current techniques of preservation have also been delineated. Further, the open questions in the area have been critically discussed. In conclusion, possible alternatives for storage, comprehensive analyses of the composition of the stored microbiome and their potential have been presented.

Beyond samples: A metric revealing more connections of gut microbiota between individuals

Studies of gut microbiota explore their complicated connections between individuals of different characteristics by applying different metrics to abundance data obtained from fecal samples. Although classic metrics are capable to quantify differences between samples, the microbiome of fecal sample is not a good surrogate for the gut microbiome of individuals because the microbial populations of the distal colon does not adequately represent that of the entire gastrointestinal tract. To overcome the deficiency of classic metrics in which the differences can be measured between the samples analyzed, but not the corresponding populations, we propose a metric for representing composition differences in the gut microbiota of individuals. Our investigation shows this metric outperforms traditional measures for multiple scenarios. For gut microbiota in diverse geographic populations, this metric presents more explainable data variance than others, not only in regular variance analysis but also in principle component analysis and partition analysis of biologic characteristics. With time-series data, the metric further presents a strong correlation with the time interval of serial sampling. Our findings suggest that the metric is robust and powerfully detects the intrinsic variations in gut microbiota. The metric holds promise for revealing more relations between gut microbiota and human health.

Optimisation of sample storage and DNA extraction for human gut microbiota studies​

Background

New developments in next-generation sequencing technologies and massive data received from this approach open wide prospects for personalised medicine and nutrition studies. Metagenomic analysis of the gut microbiota is paramount for the characterization of human health and wellbeing. Despite the intensive research, there is a huge gap and inconsistency between different studies due to the non-standardised and biased pipeline. Methodical and systemic understanding of every stage in the process is necessary to overcome all bottlenecks and grey zones of gut microbiota studies, where all details and interactions between processes are important.

Results

Here we show that an inexpensive, but reliable iSeq 100 platform is an excellent tool to perform the analysis of the human gut microbiota by amplicon sequencing of the 16 S rRNA gene. Two commercial DNA extraction kits and different starting materials performed similarly regarding the taxonomic distribution of identified bacteria. DNA/RNA Shield reagent proved to be a reliable solution for stool samples collection, preservation, and storage, as the storage of faecal material in DNA/RNA Shield for three weeks at different temperatures and thawing cycles had a low impact on the bacterial distribution.

Conclusions

Altogether, a thoroughly elaborated pipeline with close attention to details ensures high reproducibility with significant biological but not technical variations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02233-y.

On the Variability of Microbial Populations and Bacterial Metabolites within the Canine Stool. An in-Depth Analysis

Simple Summary

The present study investigated for the first time the impact that different sampling points have on the abundance of microbial populations and metabolites within the canine stool. We found that inner stool subsamples resulted in higher concentrations of bacterial metabolites but not of microbial populations. These findings suggest that stool subsampling is unlikely to represent the canine microbiota and metabolome uniformly. We believe that complete homogenisation of the whole stool prior to analysis may improve the final outcome when investigating the canine gut microbiome.

Abstract

Canine faecal microbial populations and metabolome are being increasingly studied to understand the interplay between host and gut microbiome. However, the distribution of bacterial taxa and microbial metabolites throughout the canine stool is understudied and currently no guidelines for the collection, storage and preparation of canine faecal samples have been proposed. Here, we assessed the effects that different sampling points have on the abundance of selected microbial populations and bacterial metabolites within the canine stool. Whole fresh faecal samples were obtained from five healthy adult dogs. Stool subsamples were collected from the surface to the inner part and from three equally sized areas (cranial, central, caudal) along the length axis of the stool log. All samples were finally homogenised and compared before and after homogenisation. Firmicutes, Bacteroidetes, Clostridium cluster I, Lactobacillus spp., Bifidobacterium spp. and Enterococcus spp. populations were analysed, as well as pH, ammonia and short-chain fatty acids (SCFA) concentrations. Compared to the surface of the stool, inner subsamples resulted in greater concentrations of SCFA and ammonia, and lower pH values. qPCR assay of microbial taxa did not show any differences between subsamples. Homogenisation of faeces does not affect the variability of microbial and metabolome data. Although the distribution patterns of bacterial populations and metabolites are still unclear, we found that stool subsampling yielded contradictory result and biases that can affect the final outcome when investigating the canine microbiome. Complete homogenisation of the whole stool is therefore recommended.

Impact of a Gastrointestinal Stable Probiotic Supplement Bacillus coagulans LBSC on Human Gut Microbiome Modulation

Bacillus coagulans LBSC showed stability in acidic pH, bile and simulated human gastrointenstinal juices. Under static gut model, when passed through oral, gastric and intestinal phases, B. coagulans LBSC was found to be stable as free viable spores and also with various foods such as milk and baby foods, as well as American and European diets. In human studies, modulation of gut microbiota by B. coagulans LBSC was comprehended by whole genome metagenome analysis of fecal samples obtained from pre- and post-treatment of irritable bowel syndrome (IBS) patients. B. coagulans LBSC treatment showed positive modulation in gut microbiota, especially up regulation of phyla such as Actinobacteria and Firmicutes, whereas down regulation of Bacteroids, Proteobacteria, Streptophyta and Verrucomicrobia. Simultaneously, it has altered various microbiota associated metabolic pathways to create the normalcy of gut microenvironment.

Gut microbiome comparability of fresh-frozen versus stabilized-frozen samples from hospitalized patients using 16S rRNA gene and shotgun metagenomic sequencing

Collection of faecal samples for microbiome analysis in acutely sick patients is logistically difficult, particularly if immediate freezing is required (i.e. fresh-frozen, or FF sampling). Previous studies in healthy/non-hospitalized volunteers have shown that chemical stabilization (i.e. stabilized-frozen, or SF sampling) allows room-temperature storage with comparable results to FF samples. To test this in a hospital setting we compared FF and SF approaches across 17 patients undergoing haematopoietic stem cell transplantation (HSCT) using both 16S rRNA gene and shotgun metagenomic sequencing. A paired (same stool specimen) comparison of FF and SF samples was made, with an overall comparable level in relative taxonomic abundances between the two sampling techniques. Though shotgun metagenomic sequencing found significant differences for certain bacterial genera (P < 0.001), these were considered minor methodological effects. Within-sample diversity of either method was not significantly different (Shannon diversity P_16SrRNA = 0.68 and P_shotgun = 0.89) and we could not reject the null hypothesis that between-sample variation in FF and SF were equivalent (P_16SrRNA = 0.98 and P_shotgun = 1.0). This indicates that SF samples can be used to reliably study the microbiome in acutely sick patient populations, thus creating and enabling further outcomes-based metagenomic studies on similarly valuable cohorts.