Just spin down the culture and boil the pellet with 1x SDS-PAGE sample buffer and cool down to room temperature. Then centrifuge the sample at full speed and load the supernatant. This always worked for me. I never used lysozyme and DNase for negative controls. And also check for the proper amount of culture. I think two hours is not sufficient to achieve proper growth. I hope this helps you. 

Good luck

In addition, I am afraid the single band you see may be for lysozyme (check its molecular weight). I will suggest you grow the untransformed cells for the as much time as you do with the transformed, induced cells.

Thanks Ramchandra and Robert for your suggestions . I will do as suggested and let you know if    I  have any problems .