RIBO-seq in Bacteria: a Sample Collection and Library Preparation Protocol for NGS Sequencing

Summary

Here we describe the stages of sample collection and preparation for RIBO-seq in bacteria. Sequencing of the libraries prepared according to these guidelines results in sufficient data for comprehensive bioinformatic analysis. The protocol we present is simple, uses standard laboratory equipment and takes seven days from lysis to obtaining libraries.

Abstract

The ribosome profiling technique (RIBO-seq) is currently the most effective tool for studying the process of protein synthesis in vivo. The advantage of this method, in comparison to other approaches, is its ability to monitor translation by precisely mapping the position and number of ribosomes on a mRNA transcript.

In this article, we describe the consecutive stages of sample collection and preparation for RIBO-seq method in bacteria, highlighting the details relevant to the planning and execution of the experiment.

Since the RIBO-seq relies on intact ribosomes and related mRNAs, the key step is rapid inhibition of translation and adequate disintegration of cells. Thus, we suggest filtration and flash-freezing in liquid nitrogen for cell harvesting with an optional pretreatment with chloramphenicol to arrest translation in bacteria. For the disintegration, we propose grinding frozen cells with mortar and pestle in the presence of aluminum oxide to mechanically disrupt the cell wall. In this protocol, sucrose cushion or a sucrose gradient ultracentrifugation for monosome purification is not required. Instead, mRNA separation using polyacrylamide gel electrophoresis (PAGE) followed by the ribosomal footprint excision (28-30 nt band) is applied and provides satisfactory results. This largely simplifies the method as well as reduces the time and equipment requirements for the procedure. For library preparation, we recommend using the commercially available small RNA kit for Illumina sequencing from New England Biolabs, following manufacturer's guidelines with some degree of optimization.

The resulting cDNA libraries present appropriate quantity and quality required for next generation sequencing (NGS). Sequencing of the libraries prepared according to the described protocol results in 2 to 10 mln uniquely mapped reads per sample providing sufficient data for comprehensive bioinformatic analysis. The protocol we present is quick and relatively easy and can be performed with standard laboratory equipment.

Introduction

The ribosome profiling technique (RIBO-seq) was developed in the laboratory of Jonathan Weissman at the University of California, San Francisco¹. In comparison to other methods used to study gene expression at the translational level, RIBO-seq focuses on each ribosome binding to mRNA and provides information about its location and the relative number of ribosomes on a transcript. It enables monitoring the process of protein synthesis in vivo and can provide single codon resolution and accuracy allowing the measurement of the ribosome density on both, the individual mRNA and along the entire transcriptome in the cell. At the foundation ....

Protocol

1. Sample collection

1. Prepare a bacterial culture. We recommend a culture volume of 100 mL per sample.
2. Prepare equipment and reagents for sample collection: two scoopulas per sample, sterile 0.45 µm mixed cellulose esters membrane (MCE) filters, 50 mL sterile tubes, liquid nitrogen, 50 mg/mL chloramphenicol in 70% (vol/vol) ethanol (optional). Puncture the lid of 50 mL tubes to allow liquid nitrogen evaporation and prevent the explosion of closed tubes. Decontaminate scoopulas with laboratory detergent and 70% ethanol.
3. Prewarm the filtering equipment and one of the scoopulas to growth temperature of the bacterial culture.
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Results

The exemplary results presented here were obtained in a study examining translation regulation in sporulating WT Bacillus subtilis cells. Overnight cultures were diluted to OD₆₀₀ equal to 0.1 in 100 mL of rich medium and incubated at 37 °C with vigorous shaking until OD₆₀₀ reached 0.5-0.6. The rich medium was then replaced with minimal medium to induce sporulation process and the incubation was continued for up to four hours. Cells were harvested every hour beginning with T0 - sporulation i.......

Discussion

The key technical challenge of the ribosome profiling is the need to rapidly inhibit translation in order to capture a snapshot of ribosomes on mRNAs at a particular physiological state of interest. To accomplish this, translation inhibitors, rapid harvesting and flash freezing in liquid nitrogen are commonly used. Applying antibiotics is optional since they can cause artifacts. Chloramphenicol is a commonly used drug to arrest elongating ribosomes in bacterial RIBO-seq. However, it does not prevent initiation, resulting.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
10X TBE (powder)	Invitrogen	AM9864
2-Mercaptoethanol, 99%, pure	Acros Organics	125472500
Adenosine 5'-Triphosphate (ATP)	New England Biolabs	P0756S
Aluminium oxide calcinated pure p.a.	Chempur	114560600
Calcium chloride dihydrate	Sigma-Aldrich	C3881-500G
Chloramphenicol	MP Biomedicals	190321
DNA Clean & Concentrator -5	Zymo Research	D4004
Dnase I recombinant, Rnase-free	Roche	4716728001
EDTA disodium salt	Fisher Scientific	E/P140/48
Ethyl Alcohol Absolut 99,8%  Pure-P.A.-Basic	POCH Avantor Performance Materials Poland S.A	BA6480111
Filtration apparatus	VWR Collection	511-0265	all-glass filtration apparatus, with funnel, fritted base, cap, 47 mm Ø spring clamp and ground joint flask
Gel 40 (19:1)	Rotiphorese	3030.1
Gel Loading Dye, Blue, 6X	New England Biolabs	E6138G
Guanosine 5′-[β,γ-imido]triphosphate trisodium salt hydrate	Sigma-Aldrich	G0635-25MG
labZAP	A&A Biotechnology	040-500
Magnesium acetate tetrahydrate	Sigma-Aldrich	M5661-250G
MCE membrane fiter	Alfatec Technology	M47MCE45GWS	pore size: 0.45um
MICROBExpress Bacterial mRNA Purification	Invitrogen	AM1905
Multiplex Small RNA Library Prep Set for Illumina	New England Biolabs	E7300S
Nuclease-Free Water	Ambion	AM9937
Potassium Acetate Anhydrous Pure P.A.	POCH Avantor Performance Materials Poland S.A	744330113
Quick-Load pBR322 DNA-MspI Digest	New England Biolabs	E7323A
RNA Clean & Concentrator -25	Zymo Research	R1018
Sodium acetate	Sigma-Aldrich	S2889-250G
Sodium carbonate	Sigma-Aldrich	223530-500G
Sodium hydrogen carbonate pure p.a.	POCH Avantor Performance Materials Poland S.A	810530115
SYBR Gold nucleic acid gel stain	Life Technologies	S11494
T4 Polynucleotide Kinase	New England Biolabs	M0201L
T4 Polynucleotide Kinase Reaction Buffer	New England Biolabs	B0201S
TBE-Urea Sample Buffer (2x)	Invitrogen	LC6876
Tris(hydroxymethyl)amino-methane, ultrapure, 99,9%	AlfaAesar	J65594
Triton X-100, 98%	Acros Organics	327371000
Urea G.R.	lach:ner	40096-AP0