The authors acknowledge funding from the NIAID/NIH (1R01AI137075-01), the Carver Trust Medical Research Initiative Grant, and the University of Iowa Environmental Health Sciences Research Center, NIEHS/NIH (P30 ES005605).

The protocol was approved by the Institutional Animal Care and Use Committee of the University of Iowa.
1. Fecal Sample Collection and Handling
<ol>
	<li>Sterilize the divider boxes (see Table of Materials, Supplementary Figure 1) with 70% ethanol.</li>
	<li>Pre-label microcentrifuge tubes (one per mouse) with the sample ID and treatment group (if applicable).</li>
	<li>Place the mice in sterilized divider boxes and allow them to defecate normally for up to ...

The described protocol is simple, with easy-to-follow steps to perform microbiome profiling using 16S rRNA metagenomic sequencing from a large number of biospecimens of interest. Next-generation sequencing has transformed microbial ecology studies, especially in human and pre-clinical disease models31,32. The main advantage of this technique is its ability to successfully analyze complex microbial compositions (culturable and non-culturable microbes) in a given b...

Microbiota refers to a collection of microorganisms (bacteria, viruses, archaea, bacteriophages, and fungi) living in a particular environment, and the microbiome refers to the collective genome of resident microorganisms. As bacteria are one of the most abundant microbes in humans and mice, this study is focused only on bacterial profiling. The human gut is colonized by trillions of bacteria and hundreds of bacterial strains1. The normal gut microbiota plays a vital role in maintaining a healthy state in the host by regulating functions (i.e., maintenance of an intact intestinal barrier, food metabolism, energy homeostasis, inhibition of colonization by pathogenic organisms, and regulation of immune responses)2,3,4,5. Compositional perturbations of the gut microbiota (gut dysbiosis) have been linked to a number of human diseases, including gastrointestinal disorders6, obesity7,8, stroke9, cancer10, diabetes8,11, rheumatoid arthritis12, allergies13, and central nervous system-related diseases such as multiple sclerosis (MS)14,15 and Alzheimer&#39;s disease (AD)8,16. Therefore, in recent years, there has been growing interest in tools for identifying bacterial composition at different body sites. A reliable method should have characteristics such as being high-throughput and easy-to-use, having the ability to classify bacterial microbiota with high resolution, and being low-cost.
Culture-based microbiological techniques are not sensitive enough to identify and characterize the complex gut microbiome due to the failure of several gut bacteria to grow in culture. The advent of the sequencing-based technology, especially 16S rRNA-based metagenomic sequencing, has overcome some of these challenges and transformed microbiome research17. Advanced 16S rRNA-based sequencing technology has helped in establishing a critical role for the gut microbiome in human health. The Human Microbiome Project, a National Institutes of Health initiative18, and the MetaHIT project (a European initiative)19 have both helped in establishing a basic framework for microbiome analysis. These initiatives helped kick-start multiple studies to determine the role of the gut microbiome in human health and disease.
A number of groups have shown gut dysbiosis in patients with inflammatory diseases12,14,15,20,21,22. Despite being widely used for taxonomic profiling due to the ability to multiplex and low costs, there are no uniform protocols for 16S rRNA-based taxonomic profiling. Another limitation is the low resolution of taxonomic assignment owing to smaller sequencing reads (150 bp or 250 bp) and use of only forward sequencing read (R1) due to low quality reverse sequencing reads (R2). However, advances in sequencing technology have helped to overcome some of these challenges, such as the ability to sequence longer reads using paired-end reads (e.g., Illumina MiSeq 2x300bp).
The present sequencing technology can sequence 600 bp good quality reads, which allows merging of R1 and R2 reads. These merged longer R1 and R2 reads allow better taxonomic assignments, especially with open-access R-based Divisive Amplicon Denoising Algorithm-2 (DADA2) platform. DADA2 utilizes amplicon sequence variant (ASV)-based assignments instead of operational taxonomic unit (OTU) assignments based on 97% similarity utilized by QIIME23. ASV matches result in an exact sequence match in the database within 1&#8211;2 nucleotides, which leads to assignment at genus and species levels. Thus, the combination of longer, good quality paired-end reads and better taxonomic assignment tools (such as DADA2) have transformed microbiome studies.
Provided here is a step-by-step guide for performing bacterial profiling using two-step amplification of the V3&#8211;V4 region of 16S rRNA and data analysis using DADA2, Phyloseq, and METAGENassist pipelines. For this study, human leukocyte antigen (HLA) class II transgenic mice are used, as certain HLA class II alleles are linked with a predisposition to autoimmune diseases such as MS20,24,25. However, the importance of HLA class II genes in regulating the composition of gut microbiota is unknown. It is hypothesized that the HLA class II molecule will influence gut microbial community by selecting for specific bacteria. Major histocompatibility complex (MHC) class II knockout mice (AE.KO) or mice expressing human HLA-DQ8 molecules (HLA-DQ8)24,25,26 were used in order to understand the importance of HLA class II molecules in shaping the gut microbial community. It is believed that this complete and simplified workflow with R-based data analysis will serve as an excellent tool for researchers interested in performing microbiome profiling studies.
The generation of mice lacking endogenous murine MHC class II genes (AE.KO) and AE-/-.HLA-DQA1*0103, DQB1*0302 (HLA-DQ8) transgenic mice with a C57BL/6J background has been described previously26. Fecal samples are collected from mice of both sexes (8&#8211;12 weeks of age). Mice were previously bred and maintained in the University of Iowa animal facility as per the NIH and institutional guidelines. Contamination control strategies such as weaning of the mice inside a laminar flow cabinet, changing of gloves between different strains of mice, and proper maintenance of mice are critical steps for profiling of gut microbiome.
Proper personal protective equipment (PPE) are highly recommended during the entire procedure. Appropriate negative controls should be included when performing DNA isolation, PCR1 and PCR2 amplification, and sequencing steps. Use of sterile, DNase-free, RNase-free, and pyrogen-free supplies is recommended. Designated pipettor for microbiome work and filtered pipette tips should be used throughout the protocol. Microbiota analysis consists of seven steps: 1) fecal sample collection and processing; 2) extraction of DNA; 3) 16S rRNA gene amplification; 4) DNA library construction using indexed PCR; 5) clean-up and quantification of indexed PCR (library); 6) MiSeq sequencing; and 7) data processing and sequence analysis. A schematic diagram of all protocol steps is shown in Figure 1.

<table>
	<tbody>
		<tr>
			<td>1.5 ml Natural Microcentriguge Tube</td>
			<td>USA, Scientific</td>
			<td>1615-5500</td>
			<td>Fecal collection</td>
		</tr>
		<tr>
			<td>3M hand applicator squeegee PA1-G</td>
			<td>3M, MN, US</td>
			<td>7100038651</td>
			<td>Squeeger for proper sealing of PCR Plate</td>
		</tr>
		<tr>
			<td>Agencourt AMPure XP</td>
			<td>Beckman Coulter, IN, USA</td>
			<td>A63880</td>
			<td>PCR Purification, NGS Clean-up, PCR clean-up</td>
		</tr>
		<tr>
			<td>Agilent DNA 1000 REAGENT</td>
			<td>Agilent Technologies, CA, USA</td>
			<td>5067-1504</td>
			<td>DNA quantification and quality control</td>
		</tr>
		<tr>
			<td>Bioanalyzer DNA 1000 chip</td>
			<td>Agilent Technologies, CA, USA</td>
			<td>5067-1504</td>
			<td>DNA quantification and quality control</td>
		</tr>
		<tr>
			<td>Index Adopter Replacement Caps</td>
			<td>Illumina, Inc., CA, USA</td>
			<td>15026762</td>
			<td>New cap for Index 1 and 2 adopter primer</td>
		</tr>
		<tr>
			<td>DNeasy PowerLyzer PowerSoil Kit</td>
			<td>MoBio now part of QIAGEN, Valencia, CA, USA</td>
			<td>12855-100</td>
			<td>DNA isolation</td>
		</tr>
		<tr>
			<td>KAPA HiFi HotStart ReadyMiX (2X)</td>
			<td>Kapa Biosystem, MA, USA</td>
			<td>KK2602</td>
			<td>PCR ready mix for Amplicon PCR1 and Indexed PCR2</td>
		</tr>
		<tr>
			<td>Lewis Divider Boxes</td>
			<td>Lewis Bins, WI, US</td>
			<td>ND03080</td>
			<td>Fecal collection</td>
		</tr>
		<tr>
			<td>Magnetic stand</td>
			<td>New England BioLabs, MA, USA</td>
			<td>S1509S</td>
			<td>For PCR clean-up</td>
		</tr>
		<tr>
			<td>MicroAmp Fast Optical 96-Well Reaction Plate</td>
			<td>Applied Biosystems, Thermo Fisher Scientific, CA, USA</td>
			<td>4346906</td>
			<td>PCR Plate</td>
		</tr>
		<tr>
			<td>MicroAmp Optical Adhesive Film</td>
			<td>Applied Biosystems, Thermo Fisher Scientific, CA, USA</td>
			<td>4311971</td>
			<td>PCR Plate Sealer</td>
		</tr>
		<tr>
			<td>Microfuge 20 Centrifuge</td>
			<td>Beckman Coulter, IN, USA</td>
			<td>B30154</td>
			<td>Centrifuge used for DNA isolation</td>
		</tr>
		<tr>
			<td>MiSeq Reagent Kit (600 cycles)v.3</td>
			<td>Illumina, Inc., CA, USA</td>
			<td>MS-102-3003</td>
			<td>For MiSeq Sequencing</td>
		</tr>
		<tr>
			<td>Nextera XT DNA Library Preparation Kit</td>
			<td>Illumina, Inc., CA, USA</td>
			<td>FC-131-1001</td>
			<td>16S rRNA DNA Library Preparation</td>
		</tr>
		<tr>
			<td>Reagent Reservoirs Multichannel Trays</td>
			<td>ASI, FL,USA</td>
			<td>RS71-1</td>
			<td>For Pooling of PCR2 Product</td>
		</tr>
		<tr>
			<td>Plate Cetrifuge</td>
			<td>Thermo Fisher Scientific, CA, USA</td>
			<td>75004393</td>
			<td>For PCR reagent mixing and removing air bubble from Plate</td>
		</tr>
		<tr>
			<td>PhiX Control</td>
			<td>Illumina, Inc., CA, USA</td>
			<td>FC-110-3001</td>
			<td>For MiSeq Sequencing control</td>
		</tr>
		<tr>
			<td>Microbiome DNA Purification Kit</td>
			<td>Thermo Fisher Scientific, CA, USA</td>
			<td>A29789</td>
			<td>For purification of PCR1 product</td>
		</tr>
		<tr>
			<td>PowerLyzer 24 Homogenizer</td>
			<td>Omni International, GA, USA</td>
			<td>19-001</td>
			<td>Bead beater for DNA Isolation</td>
		</tr>
		<tr>
			<td>Qubit dsDNA HS (High Sensitivity) assay kit</td>
			<td>Thermo Fisher Scientific, CA, USA</td>
			<td>Q32854</td>
			<td>DNA quantification</td>
		</tr>
		<tr>
			<td>TruSeq Index Plate Fixture</td>
			<td>Illumina, Inc., CA, USA</td>
			<td>FC-130-1005</td>
			<td>For Arranging of the index primers</td>
		</tr>
		<tr>
			<td>Vertical Dividers (large)</td>
			<td>Lewis Bins, WI, US</td>
			<td>DV-2280</td>
			<td>Fecal collection</td>
		</tr>
		<tr>
			<td>Vertical Dividers (small)</td>
			<td>Lewis Bins, WI, US</td>
			<td>DV-1780</td>
			<td>Fecal collection</td>
		</tr>
	</tbody>
</table>

microbiota analysis using two-step pcr and next-generation 16s rrna gene sequencing

The human gut is colonized by trillions of bacteria that support physiologic functions such as food metabolism, energy harvesting, and regulation of the immune system. Perturbation of the healthy gut microbiome has been suggested to play a role in the development of inflammatory diseases, including multiple sclerosis (MS). Environmental and genetic factors can influence the composition of the microbiome; therefore, identification of microbial communities linked with a disease phenotype has become the first step towards defining the microbiome&#8217;s role in health and disease. Use of 16S rRNA metagenomic sequencing for profiling bacterial community has helped in advancing microbiome research. Despite its wide use, there is no uniform protocol for 16S rRNA-based taxonomic profiling analysis. Another limitation is the low resolution of taxonomic assignment due to technical difficulties such as smaller sequencing reads, as well as use of only forward (R1) reads in the final analysis due to low quality of reverse (R2) reads. There is need for a simplified method with high resolution to characterize bacterial diversity in a given biospecimen. Advancements in sequencing technology with the ability to sequence longer reads at high resolution have helped to overcome some of these challenges. Present sequencing technology combined with a publicly available metagenomic analysis pipeline such as R-based Divisive Amplicon Denoising Algorithm-2 (DADA2) has helped advance microbial profiling at high resolution, as DADA2 can assign sequence at the genus and species levels. Described here is a guide for performing bacterial profiling using two-step amplification of the V3-V4 region of the 16S rRNA gene, followed by analysis using freely available analysis tools (i.e., DADA2, Phyloseq, and METAGENassist). It is believed that this simple and complete workflow will serve as an excellent tool for researchers interested in performing microbiome profiling studies.

As MHC class II molecules (HLA in humans) are central players in the adaptive immune response and show strong associations with a predisposition to MS24,25,26, it was hypothesized that the HLA class II molecule would influence gut microbial composition. Therefore, mice lacking the MHC class II gene (AE.KO) or expressing human HLA-DQ8 gene (HLA-DQ8) were utilized to understand the importance of HLA class II molecules in shaping t...

Watch this Scientific Journal Video about Microbiota Analysis Using Two-step PCR and Next-generation 16S rRNA Gene Sequencing at JoVE.com

Microbiota Analysis Using Two-step PCR and Next-generation 16S rRNA Gene Sequencing

Described here is a simplified standard operating procedure for microbiome profiling using 16S rRNA metagenomic sequencing and analysis using freely available tools. This protocol will help researchers who are new to the microbiome field as well as those requiring updates on methods to achieve bacterial profiling at a higher resolution.

The human gut is colonized by trillions of bacteria that support physiologic functions such as food metabolism, energy harvesting, and regulation of the ...

Profiling of microbiome is the first step toward defining the role of microbiome in health and disease.Here, we are describing a simple procedure for isolating high-quality bacterial DNA from fecal sample preparing library, performing 16SR RNA and a meta genomic sequencing and microbiome data analysis.This protocol will help researchers new to microbiome field, as well as researchers working in microbiome field in establishing the microbiome pipeline in their lab.This protocol can be extended for profiling of microbiome from other bio specimens such as nasal, oral, or skin samples of animal and human subjects.Bead picking is the most important steps as all downstream steps are depend on high quality DNA.Proper sealing of preserve plate is important as incomplete sealing might lead to the oppressing of amplified product resulting in low quality sequencing data.To begin, sterilize the divider boxes with 70%ethanol.Place the mice in sterilized divider boxes and allow them to defecate normally for up to one hour.Use sterile forceps to collect the fecal pellets in an empty pre-labeled 1.5 milliliter micro centrifuge tube.Enclose the tube securely.Sterilize the forceps with 70%ethanol, followed by a germicidal disposable wipe, after collecting fecal from each mouse.Weigh 200 milligrams of fecal pellets into a 1.5 milliliter micro centrifuge tube, with 0.1 milliliter glass beads, and place the bead tube into a bead beating homogenizer and homogenize the samples for 45 seconds at room temperature, at a speed of 4.5 meters per second.Extract DNA as per instructions of the kit manufacturer and elute DNA in a 1.5 milliliter micro centrifuge tube.After isolating DNA, quantify the isolated DNA by loading 1 microliter of the DNA on a fluorometer.Setup 16S ribosomal RNA gene amplification PCR1 in a 96-Well PCR plate, using a 25 microliter reaction volume.Using a multi-channel pipette, add 40 nano grams of DNA, 13.5 micro liters of 2X high-fidelity polymerase enzyme mix, containing buffer, plus DNTPs in forward and reverse primer.Seal the PCR plate properly from the top to the bottom in along all four edges.And centrifuge at 1000 times G at 20

Microbiota Analysis Using Two-step PCR and Next-generation 16S rRNA Gene Sequencing

Abstract