Killing Buffer is used to kill bacterial cells. Usually one would use cold Killing buffer in a 50:50 ratio to harvest cells in liquid medium. The buffer contains NaN3 and kills the cells quickly. Fast killing and down cooling is important for example to stop RNases if you want to isolate RNA from that specific time point of cell growth.
Endconzentration will be 20mM Tris and 5mM MgCl2 and 20mM NaN3
for 1 liter
2 ml 1M Tris-HCl pH 7.5
0.5 ml 1M MgCl2
1.3 g NaN3
997.5 ml ddH2O
Store at 4°C.
Note that NaN3 is highly toxic and should be handled accordingly.