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Gram-negative bacterial DNA


Introduction

This protocol describes a method for DNA extraction from E. coli, as an example of a Gram-negative bacteria. We recommend growing a culture to OD ~0.7, and extracting the DNA using the QIAGEN Genomic-tip 500/G columns. These are easy to use, do not require the use of phenol or chloroform, and give a consistently high yield. We have found that incubating the culture with chloramphenicol for 1 hour before collection resulted in a 4.5X increase in yield (from 7.4 µg to 33.9 µg). Addition of this antibiotic stops cell division, but still enables completion of DNA replication.

Materials

Method

  1. Culture the E. coli cells until the OD reaches 0.5.

  2. Add chloramphenicol to the culture to a final concentration of 180 µg/ml. Incubate the culture for another hour (at the end, the OD should be ~0.7). Remove 10 ml of culture for extraction.

  3. Follow the QIAGEN Genomic-tip 500/G protocol. Elute the purified DNA into 200 μl TE buffer, pH 8, and leave at room temperature until all DNA has dissolved.

  4. Critical Step: If after several hours some precipitation is still visible in the sample, this could indicate protein contamination. In this case, spin down the sample in a microfuge for 1 min at 10,000 g, and carefully remove the supernatant.

Results

  • Yield: 33.9 µg
  • OD 260/280: 1.89
  • OD 260/230: 2.29

-ve


- **Fragment size: 1.3 - 165kb (FEMTO pulse)**

-ve frag

Sequencing performance

Libraries for Nanopore sequencing were prepared using the Ligation Sequencing Kit, with g-TUBE fragmentation.

  • Read length profile after fragmentation and sequencing:

-ve seq

Last updated: 7/11/2023

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