Abstract: Studies in humans and large animals indicate a relationship between the uterine microbiome composition and endometrial receptivity. Despite many studies have been performed, the analysis of the uterine microbiome remains challenging due to the very low microbial biomass. Studies in other biological systems showed that RNA-based microbiome analysis complements DNA-based results and provides information about active bacteria in a sample. Thus, the aim of this study was to establish a highly sensitive and specific 16S rRNA gene V3-V4 amplicon PCR from equine uterine cytobrush samples and to compare DNA- and RNA-based 16S rRNA microbiome analysis. An optimized 16S rRNA gene V3-V4 amplicon PCR protocol from equine uterine cytobrush samples was developed, which was able to detect less than 38 bacterial genome copies using a bacterial DNA community standard. For the RNA-based amplicon generation protocol starting from cDNA, at least a 10-fold higher sensitivity was estimated compared to DNA-based approach. The comparison of using RNA and DNA isolated from the same uterine cytobrush samples as input for 16S V3-V4 amplicon sequencing revealed a much higher number of amplicon sequence variants as well as taxonomic units for the RNA-based approach. This resulted in significant differences in alpha (Simpson, Chao1) and beta diversity between RNA- and DNA-based analysis. Differential abundance analysis revealed significant differences between DNA and RNA samples at all taxonomic levels. Despite these differences, the overall microbiome composition was similar between the paired DNA and RNA samples. Many differences were probably found due to the higher sensitivity of the RNA-based approach. Furthermore, the DNA-based analysis is biased by the rRNA gene copy numbers (1-21), and the RNA-based analysis by the number of ribosomes per cell, which was reflected in the differences in the microbiome composition between the approaches. In addition, the results suggested that the DNA-based analysis is detecting cell-free bacterial DNA and/or DNA of dead bacteria that could be present in the samples. Altogether, the obtained results indicate advantages of a combined DNA- and RNA-based microbiome analysis, offering complementary and valuable information in the context of fertility-related studies of the uterine microbiome.
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Research Overview
This study aimed to develop and compare RNA- and DNA-based 16S rRNA gene sequencing methods to analyze the uterine microbiome in horses, focusing on determining which approach offers greater sensitivity and insights into active bacterial populations.
The research highlights that RNA-based analyses detect more bacterial variants and may be more sensitive in identifying active bacteria than DNA-based analyses, which can detect both live and dead bacterial DNA.
Background and Motivation
The uterine microbiome affects endometrial receptivity and fertility in both humans and large animals.
Studying the uterine microbiome is challenging due to its very low microbial biomass, making sensitive detection methods necessary.
Previous research in other biological systems showed that RNA-based microbiome analyses provide complementary information by focusing on metabolically active bacteria, while DNA-based methods capture total bacterial presence, alive or dead.
This study aims to establish a sensitive protocol specifically for equine uterine samples and to compare RNA- versus DNA-based 16S rRNA gene sequencing of the uterine microbiome.
Methodology
Sample Collection: Equine uterine samples were collected using cytobrushes to obtain cells and associated bacteria.
PCR Optimization: Developed a highly sensitive PCR protocol targeting the V3-V4 region of the 16S rRNA gene optimized for low bacterial biomass samples.
Sensitivity Assessment: Used bacterial DNA community standards to quantify the limit of detection, achieving detection of fewer than 38 genome copies for the DNA-based method.
RNA-Based Approach: Converted RNA extracted from the samples into cDNA to perform PCR, estimating at least a 10-fold increased sensitivity compared to the DNA-based method.
Sequencing and Analysis: Performed 16S rRNA gene amplicon sequencing on paired RNA and DNA samples from the same uterine cytobrushes to directly compare diversity and composition results.
Key Findings
Higher Sensitivity of RNA-based Method: The RNA-derived cDNA approach detected a substantially higher number of amplicon sequence variants (ASVs) and taxonomic units.
Diversity Differences: Significant differences in alpha diversity metrics (Simpson, Chao1) and beta diversity were observed between RNA- and DNA-based analyses, indicating distinct microbial community profiles.
Microbiome Composition: Despite differences, overall bacterial community composition was broadly similar between paired RNA and DNA samples.
Taxonomic Differences: Differential abundance analysis showed significant variation at every taxonomic level between DNA and RNA samples.
Potential Biases in Methods: DNA-based results may be influenced by variable rRNA gene copy numbers (1-21 copies per genome) and may detect DNA from dead or cell-free bacteria.
RNA-based analysis: Reflects bacterial activity based on ribosome numbers within living cells, providing additional insight into active microbiota.
Interpretation and Implications
The RNA-based approach’s higher sensitivity likely accounts for detection of a greater diversity and more active members of the uterine microbiome.
The DNA-based method offers detection of total bacterial DNA, including dead organisms and free DNA, which may complicate interpretation regarding active bacterial populations.
Combining RNA- and DNA-based analyses captures complementary aspects of the uterine microbiome, encompassing both presence and activity of microbial communities.
This combined analysis is particularly valuable for fertility studies, where understanding metabolically active bacteria could lead to better insights into uterine health and reproductive success.
The optimized protocols developed in this study provide a methodological framework for sensitive and specific microbiome analysis in samples with low bacterial biomass.
Conclusions
This study establishes that RNA-based 16S rRNA sequencing is more sensitive and reveals a broader range of active bacteria in the uterine environment compared to DNA-based methods.
Significant differences in detected microbial diversity highlight methodological biases inherent in RNA versus DNA approaches.
Integration of RNA- and DNA-derived sequencing data yields complementary insights, suggesting a combined approach is optimal for comprehensive uterine microbiome characterization.
These findings provide important technical guidance and biological insights for future research on the role of the uterine microbiome in reproductive health.
Cite This Article
APA
Dyroff AI, López-Valiñas Á, Magalhaes HB, Podico G, Canisso IF, Almiñana C, Bauersachs S.
(2025).
Comparison of RNA- and DNA-based 16S amplicon sequencing to find the optimal approach for the analysis of the uterine microbiome.
Sci Rep, 15(1), 17037.
https://doi.org/10.1038/s41598-025-00969-5
Institute of Veterinary Anatomy, Vetsuisse Faculty Zurich, University of Zurich, Lindau (ZH), Switzerland. antoniaisabelle.dyroff@uzh.ch.
López-Valiñas, Álvaro
Institute of Veterinary Anatomy, Vetsuisse Faculty Zurich, University of Zurich, Lindau (ZH), Switzerland.
Magalhaes, Humberto B
College of Veterinary Medicine, University of Illinois Urbana-Champaign, Urbana, IL, USA.
Podico, Giorgia
College of Veterinary Medicine, University of Illinois Urbana-Champaign, Urbana, IL, USA.
Canisso, Igor F
College of Veterinary Medicine, University of Illinois Urbana-Champaign, Urbana, IL, USA.
Almiñana, Carmen
Institute of Veterinary Anatomy, Vetsuisse Faculty Zurich, University of Zurich, Lindau (ZH), Switzerland.
Department of Reproductive Endocrinology, University Hospital Zurich, Zurich, Switzerland.
Bauersachs, Stefan
Institute of Veterinary Anatomy, Vetsuisse Faculty Zurich, University of Zurich, Lindau (ZH), Switzerland. stefan.bauersachs@uzh.ch.
MeSH Terms
Female
Animals
RNA, Ribosomal, 16S / genetics
Microbiota / genetics
Uterus / microbiology
DNA, Bacterial / genetics
Horses
Bacteria / genetics
Bacteria / classification
Sequence Analysis, DNA / methods
RNA, Bacterial / genetics
Grant Funding
200534 / Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung
Conflict of Interest Statement
Declarations. Competing interests: The authors declare no competing interests. Ethics approval and consent to participate: The samples were collected from mares owned by the University of Illinois Urbana-Champaign or from client-owned mares presented at the Veterinary Hospital (IACUC ethical approvals 21237 and 21238, respectively).
References
This article includes 74 references
Stinson LF, Boyce MC, Payne MS, Keelan JA. The Not-so-Sterile womb: evidence that the human fetus is exposed to Bacteria prior to birth.. 1124 (2019).
Banchi P, Colitti B, Opsomer G, Rota A, Van Soom A. The dogma of the sterile uterus revisited: Does microbial seeding occur during fetal life in humans and animals?. .
Vetrovsky T, Baldrian P. The variability of the 16S rRNA gene in bacterial genomes and its consequences for bacterial community analyses.. e57923 (2013).
Ortiz JO, Forster F, Kurner J, Linaroudis AA, Baumeister W. Mapping 70S ribosomes in intact cells by cryoelectron tomography and pattern recognition.. 334–341 (2006).
Fegatella F, Lim J, Kjelleberg S, Cavicchioli R. Implications of rRNA Operon copy number and ribosome content in the marine oligotrophic Ultramicrobacterium Sphingomonas Sp. strain RB2256.. 4433–4438 (1998).
Yamada H. Structome analysis of Escherichia coli cells by serial ultrathin sectioning reveals the precise cell profiles and the ribosome density.. 283–294 (2017).
Yamada H. Mycolicibacterium Smegmatis, basonym Mycobacterium Smegmatis, expresses morphological phenotypes much more similar to Escherichia coli than Mycobacterium tuberculosis in quantitative structome analysis and CryoTEM examination.. 1992 (2018).
Takahashi S, Tomita J, Nishioka K, Hisada T, Nishijima M. Development of a prokaryotic universal primer for simultaneous analysis of Bacteria and Archaea using next-generation sequencing.. e105592 (2014).
Stinson LF, Keelan JA, Payne MS. Identification and removal of contaminating microbial DNA from PCR reagents: impact on low-biomass Microbiome analyses.. 2–8 (2019).
Kawasaki A, Ryan PR. Peptide nucleic acid (PNA) clamps to reduce Co-amplification of plant DNA during PCR amplification of 16S rRNA genes from endophytic Bacteria.. 123–134 (2021).
von Wintzingerode F, Landt O, Ehrlich A, Gobel UB. Peptide nucleic acid-mediated PCR clamping as a useful supplement in the determination of microbial diversity.. 549–557 (2000).
Abellan-Schneyder I, Schusser AJ, Neuhaus KD. DdPCR allows 16S rRNA gene amplicon sequencing of very small DNA amounts from low-biomass samples.. 349 (2021).
Chao A, Chazdon RL, Colwell RK, Shen TJ. A new statistical approach for assessing similarity of species composition with incidence and abundance data. (2005).
Stinson LF, Keelan JA, Payne MS. Characterization of the bacterial Microbiome in first-pass meconium using Propidium monoazide (PMA) to exclude nonviable bacterial DNA. 378–385 (2019).
Stoddard SF, Smith BJ, Hein R, Roller BR, Schmidt TM. RrnDB: improved tools for interpreting rRNA gene abundance in bacteria and archaea and a new foundation for future development. D593–598 (2015).
Kembel SW, Wu M, Eisen JA, Green JL. Incorporating 16S gene copy number information improves estimates of microbial diversity and abundance. e1002743 (2012).
Matamouros S. Growth-rate dependency of ribosome abundance and translation elongation rate in Corynebacterium glutamicum differs from that in Escherichia coli. 5611 (2023).
Smith KE, Garza AL, Robinson C, Ashley RL, Ivey SL. 1039 WS influence of sampling location and pregnancy on composition of the Microbiome associated with the reproductive tract of the Ewe. 498–498 (2016).
Salonen A. Comparative analysis of fecal DNA extraction methods with phylogenetic microarray: effective recovery of bacterial and archaeal DNA using mechanical cell Lysis. 127–134 (2010).
Yap M, O’Sullivan O, O’Toole PW, Cotter PD. Development of sequencing-based methodologies to distinguish viable from non-viable cells in a bovine milk matrix: A pilot study. 1036643 (2022).
Han D, Zhen H, Liu X, Zulewska J, Yang Z. Organelle 16S rRNA amplicon sequencing enables profiling of active gut microbiota in murine model. 5715–5728 (2022).
Nguyen TT, Miyake A, Tran TTM, Tsuruta T, Nishino N. The relationship between uterine, fecal, bedding, and airborne dust microbiota from dairy cows and their environment: A pilot study. .
Casaro S. Integrating uterine Microbiome and metabolome to advance the Understanding of the uterine environment in dairy cows with metritis. 30 (2024).