Is your sonicator in good working condition? I notice that you asked a question a few months ago saying that you were having a problem with lysing cells by sonication, which suggests to me that you have a problem with your sonicator and/or your lysis protocol. I suggest that you have your sonicator serviced/fixed first and get a reliable lysis protocol established before trying to go on.

Hello Rithika, I agree with Samuel in that it could be an issue with your sonicator’s power source or the probe. I myself had this issue with a sonicator in the past. When you say that lysis via sonication was not successful, how do you know? Did you check the whole cell lysate, before and after sonication, and lysate supernatant on an SDS-PAGE? If you are not seeing any bands corresponding to the endogenous cellular proteins on SDS-PAGE that is a tell-tale sign that the issue is lysis. Good luck!

Just to follow-up, the sonicator could be OK but you may need to play with the settings. Try varying the amplitude. For example, you could grow a mid-size culture (50 mL) overnight, pellet the cells, and resuspend them with 12 mL of lysis buffer. Aliquot the resuspended cells into 11 tubes (1 mL each) and then, using a small sonicator probe, lyse the cells in each tube using an amplitude of either 0 (no lysis), 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100. Save a 50 uL sample of each whole cell lysate, centrifuge each sample, and transfer the lysate supernatants to new tubes. Run all whole cell lysates and lysate supernatants on an SDS-PAGE. This experiment willl help determine the optimal amplitude for cell lysis. Lysis time and volume (for heat dissipation and protein solubilization) are two other variables that will need to be optimized. First check the whole cell lysate first to ensure that your protein is expressed to begin with. Good luck!