When I want high recovery of genomic DNA I start by treating the cells with lysozyme. To that end I include the instructions from Sigma lysozyme pdf referred to in link below and also attached

Once you have incubated with lysozyme you can then proceed with extraction according to SOP provided with your Sigma genomic extraction kit

https://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/Sigma/Datasheet/7/l7651dat.pdf

Incubate E. coli (strain ATCC 37017) bearing the

pBR322 plasmid overnight in Terrific Broth (Catalog

Number T0918) with 25 mg/ml tetracycline (Catalog

Number T3383) and 25 mg/ml ampicillin (Catalog

Number A9518).

2. Centrifuge 1–2 ml samples of the overnight culture.

3. Resuspend the pellets in 350 ml of STET buffer

(10 mM Tris-HCl, pH 8.0, with 0.1 M NaCl, 1 mM

EDTA, and 5% [w/v] TRITONÒ X-100).

4. Add 25 ml of a freshly prepared lysozyme solution

(10 mg/ml in 10 mM Tris-HCl, pH 8.0).

5. Mix by vortexing for 3 seconds.

6. Incubate the lysis mixture for 30 minutes at 37 °C

7. After incubation, place the tube containing the lysis

mixture in a boiling water bath for exactly

40 seconds.

8. Centrifuge the lysis mixture at 14,000 ´ g.

9. Remove the pellet (cell debris) from the tube using

a sterile toothpick.

10. Plasmid DNA from the supernatant may then be

purified and analysed.

As @LaurenceStuartHall mentioned, lysozyme works really good to me. Maybe you can try using other protocol because sometimes using a kit is not really helpful and they're a quite expensive.

Hi,

You may find these articles useful:

Nucleic Acids Res. 1991 Apr 25; 19(8): 1955.

A simple method for the isolation of chromosomal DNA from gram positive or acid-fast bacteria. C Bollet, M J Gevaudan, X de Lamballerie, C Zandotti, and P de Micco

Indian J Microbiol. 2010 Oct; 50(4): 412–418.

A Simple Method for the Efficient Isolation of Genomic DNA from Lactobacilli Isolated from Traditional Indian Fermented Milk (dahi)

Sachinandan De,corresponding author1 Gurpreet Kaur,1 Amit Roy,1 Gaurav Dogra,2 Ramakant Kaushik,1 Paras Yadav,1 Rameshwar Singh,2 Tirtha Kumar Datta,1 and Surender Lal Goswami1

Dear abhilek,

I am agree with the statement of dr. katiria. you just once go for manual method according to sambrook. and see what happen.

the best way is boiling 10 mint then centrifugal at high speed then collect the upper layer.