why EDTA is used for lysozyme action

[ChenHA]

chiranjit chowdhury wrote:
> Dear friends, I got protocol from pharmacia for Gram negative bacterial cell
> lysis with lysozyme and EDTA. I have gone through several literature where
> they have used EDTA with lysozyme mediated cell lysis of Gram negative
> bacteria but not in case of Gram positive bacteria.
> Can anybody tell me why EDTA is used specially for Gram negative bacteria,
> the exact mechanism behind it
> Regards.
> 
> 

EDTA chelates divalent cations like calcium and magnesium.  IIRC, these 
divalent cations are important for maintaining the structures on the 
cell surface.  Removing them destablises these cell surface structures 
and makes it easier to lyse the cells.

As far as I can remember, having too much as well as too little calcium 
and magnesium can change the cell surface structures which, if I am 
remember correctly, is I think one reason why you use calcium when you 
prepare competent cells to make the cells more permeable to DNA (calcium 
also help screen out the charges allowing the DNA to stick to the cell 
surface).