How to Extract DNA from Plant Cells, Bacteria, and Tissue: Step-by-Step Protocol

PCR failure traced back to polysaccharide contamination or phenolic carryover wastes samples and delays results. Shearing genomic DNA during mixing, or skipping a proper cleanup step, compounds the problem. This guide gives you exact buffers, temperatures, and cleanup choices to follow the how to extract DNA from plant cells protocol from lysis through quality verification, so you produce PCR-ready DNA on the first attempt.

When to Use This Protocol: Matrices, Workflows, and Expected Yields

Use this protocol when PCR inhibition from polysaccharides, polyphenols, or residual detergents is a real risk. It covers plants, Gram-negative and Gram-positive bacteria, and soft animal tissues.

The workflow feeds directly into PCR, qPCR, Sanger sequencing, barcoding, and genotyping. It scales from single tubes up to 96-well batches and balances yield with effective inhibitor removal. For a broader overview of the principles behind cell lysis and nucleic acid recovery, see this guide on DNA extraction principles and steps for molecular biology research.

This guide compares CTAB, SDS/Proteinase K, and silica spin-column cleanup so you can match your approach to matrix complexity, throughput, and safety constraints.

What You Need: Equipment, Reagents, and Safety Gear

Equipment

You need a microcentrifuge capable of 12,000 to 16,000 x g, a vortex mixer with a low-speed setting, and a heat block or water bath configurable at 37 °C, 55 to 65 °C. For tough plant tissue, use a bead beater or liquid nitrogen with a mortar and pestle. Use filter tips throughout, and switch to wide-bore tips when handling high-molecular-weight DNA to prevent shearing.

Core Reagents

The primary lysis buffer for plant tissue is CTAB buffer: 2% CTAB, 100 mM Tris-HCl pH 8.0, 20 mM EDTA, 1.4 M NaCl. Add polyvinylpyrrolidone (PVP) at 1 to 2% for phenolic-rich plant varieties. Add beta-mercaptoethanol (0.2%) fresh immediately before use when oxidative browning is likely.

For bacterial and tissue lysis, prepare lysozyme at 1 mg/mL, a 10% SDS stock, Proteinase K at 20 mg/mL, and RNase A at 10 mg/mL. Sigma-Aldrich's Nucleic Acid Purification range covers gDNA purification kits, reaction clean-up columns, and individual reagents that integrate directly into this workflow without requiring buffer reformulation.

Cleanup and Precipitation Reagents

For organic extraction, use chloroform:isoamyl alcohol (24:1) or phenol:chloroform:isoamyl alcohol (25:24:1). For silica-column cleanup, prepare a guanidinium-based binding buffer per kit instructions. For precipitation, you need 100% isopropanol or 100% ethanol, 70% ethanol wash, 3 M sodium acetate pH 5.2, and TE buffer or nuclease-free water for resuspension.

Optional Spike-In Control

Add 1 ng of lambda DNA post-lysis as a recovery control. This lets you monitor extraction efficiency consistently across runs without altering your sample chemistry.

Prepare and Lyse Plant, Bacterial, and Tissue Samples

Prewarm CTAB buffer to 65 °C before you begin. Keep samples cold during homogenisation, then shift to the incubation temperature to complete lysis. Do not vortex vigorously once lysis buffer contacts the sample.

Plant Samples

1. Weigh 50 to 100 mg of young leaf tissue into a pre-chilled microcentrifuge tube.
2. Add liquid nitrogen and grind immediately to a fine powder using a mortar and pestle or bead beater. Do not let the tissue thaw before adding buffer.
3. Transfer powder to a new 1.5 mL nuclease-free tube. Add 600 to 800 µL of prewarmed CTAB buffer containing 1 to 2% PVP and 0.2% beta-mercaptoethanol.
4. Mix by gentle inversion 10 to 15 times. Avoid shaking.
5. Incubate at 65 °C for 10 to 15 minutes, inverting the tube every 3 minutes, until the lysate visibly clears.

Bacterial Pellets

1. Centrifuge 1 mL of overnight bacterial culture at 10,000 x g for 2 minutes. Discard the supernatant completely.
2. Resuspend the pellet in 180 µL TE buffer containing lysozyme at 1 mg/mL.
3. Incubate at 37 °C for 30 minutes with gentle agitation. For Gram-positive strains with thick peptidoglycan walls, extend this step to 45 to 60 minutes or supplement with mutanolysin.
4. Add 20 µL of 10% SDS (1% final concentration) and 20 µL Proteinase K at 20 mg/mL (0.2 mg/mL final).
5. Incubate at 55 °C for 30 minutes with gentle mixing until the lysate becomes clear and viscous.

Animal or Soft Plant Tissues

1. Cut 10 to 25 mg of tissue on a clean, pre-chilled surface. Transfer to a 1.5 mL tube immediately.
2. Add 400 to 600 µL of lysis buffer containing 1% SDS. Homogenise with a plastic pestle or a bead mill until no visible chunks remain.
3. Add Proteinase K to a final concentration of 0.2 mg/mL.
4. Incubate at 56 °C for 30 to 60 minutes, with occasional mixing, until the lysate is uniform and viscous.

TCI's Plant Biotechnology reagents include tissue culture and sample preparation reagents that support lysis buffer preparation for challenging plant matrices, reducing the formulation steps before you reach the extraction stage.

Remove Proteins, Cell Debris, and Polysaccharides

This stage separates clean aqueous DNA from proteins, lipids, and carbohydrates. Choose your cleanup route based on matrix complexity, available equipment, and throughput needs.

CTAB Organic Extraction (Plant Lysates)

1. Cool the lysate to room temperature. If NaCl concentration is below 0.7 M, adjust before proceeding.
2. Add an equal volume of chloroform:isoamyl alcohol (24:1). Cap the tube and mix by gentle inversion for 1 minute inside a fume hood.
3. Centrifuge at 12,000 x g for 10 minutes at room temperature.
4. Transfer only the upper aqueous phase to a new tube. Avoid disturbing the white interphase, which contains polysaccharides and denatured proteins.
5. Repeat the extraction if the interphase layer is large or the aqueous phase appears turbid.

SDS/Proteinase K Lysates (Bacterial or Tissue)

1. Add an equal volume of phenol:chloroform:isoamyl alcohol (25:24:1) or chloroform:isoamyl alcohol (24:1) to the cleared lysate.
2. Mix by gentle inversion for 1 minute. Centrifuge at 12,000 x g for 10 minutes.
3. Transfer the aqueous upper phase carefully to a fresh tube. Repeat if protein contamination (white band at interface) is heavy.

Silica Spin-Column Cleanup (All Sample Types)

1. Mix the cleared lysate 1:1 to 1:3 with guanidinium-based binding buffer, following kit-specific guidance.
2. Load up to 700 µL per spin onto the column. Centrifuge at 8,000 x g for 1 minute. Discard the flow-through. Repeat until all lysate has been loaded.
3. Wash the membrane twice with ethanol-containing wash buffer. Centrifuge 1 minute between washes.
4. Perform a dry spin at maximum speed for 1 minute to remove residual ethanol before elution.

Precipitate, Wash, and Rehydrate Genomic DNA

Precipitation from Aqueous Phase

1. Add 0.1 volume of 3 M sodium acetate pH 5.2 to the aqueous phase and mix by inversion.
2. Add either 0.6 volumes of 100% isopropanol or 2 volumes of 100% ethanol. Mix gently by inversion until DNA strands become visible as a white precipitate or fibrous mass.
3. Incubate at room temperature for 10 to 30 minutes, or at 4 °C for up to 1 hour for lower-concentration samples.
4. Centrifuge at 12,000 to 16,000 x g for 10 minutes. Carefully decant the supernatant without disturbing the pellet.
5. Add 1 mL of 70% ethanol to wash the pellet. Invert gently several times, then centrifuge for 5 minutes. Remove all ethanol with a pipette.

Drying and Resuspension

1. Air-dry the pellet for 5 to 10 minutes at room temperature until it appears just translucent. Do not overdry; a glassy white pellet will not dissolve readily.
2. Resuspend in 50 to 100 µL of TE buffer (10 mM Tris-HCl pH 8.0, 1 mM EDTA) or nuclease-free water.
3. If RNA removal is needed, add RNase A to 10 µg/mL and incubate at 37 °C for 15 minutes. Follow with a brief ethanol precipitation or a silica column pass to remove the enzyme.

Elution from Silica Columns

1. Pre-warm elution buffer or nuclease-free water to 65 to 70 °C.
2. Apply 50 to 100 µL directly to the centre of the membrane. Let it stand on the column for 1 to 5 minutes.
3. Centrifuge to recover the eluate. A second elution step with 30 to 50 µL recovers residual DNA if yield is a priority.

Verify DNA Quality and Quantify for Downstream PCR

Measure absorbance at 260 nm to quantify DNA concentration. A260/A280 of 1.8 to 2.0 indicates acceptable protein removal. A260/A230 above 2.0 confirms that salts, CTAB, and guanidinium residues are absent.

Plant CTAB preparations sometimes show A260/A230 ratios of 1.8 to 2.0 yet still amplify cleanly in PCR, provided polysaccharides were removed during the organic extraction step. Do not discard a sample purely on the basis of a borderline A260/A230 value; run a test PCR first.

For gel verification, run 50 to 100 ng on a 0.8 to 1% agarose gel. Intact, high-molecular-weight genomic DNA migrates as a tight band near the top of the gel with minimal smearing. A diffuse smear indicates degradation, and RNA contamination produces a bright low-molecular-weight band that RNase A treatment resolves. For PCR setup and amplification troubleshooting downstream, refer to the guide on PCR principles and steps for molecular biology workflows.

For PCR reactions, use 10 to 100 ng of template DNA per 25 µL reaction depending on target complexity and primer design. If your purity ratios drift below acceptable thresholds, return to this how to extract DNA from plant cells protocol and check the lysis and cleanup stages before repeating the run.

Troubleshooting and Performance Tips: Yield, Purity, and Reagent Stability

Apply the how to extract DNA from plant cells protocol tips consistently when purity ratios drift between batches. Reagent condition is a common but overlooked cause. Proteinase K is stable at minus 20 °C; degraded stock loses activity and leaves protein contamination that suppresses A260/A280. RNase A can be heat-treated at 100 °C for 15 minutes to inactivate co-purifying DNases. Guanidinium buffers must remain tightly capped to prevent moisture uptake, which dilutes their binding efficiency. CTAB buffer can crystallise at room temperature; warm it to 65 °C to clarify before use.

Frequently Asked Questions