weigh an eppendorf 诉tube, collect bacterial colo动鲜nies from culture (usually 来自petri dishes), weigh the tube again, add saline or buffer to make a concentration of 10 mg/ml. For instance, you have co尔支究含切助施叫llected 5 mg, resuspend in 0.5 ml solution, that is still 10/ml. If you collect more, resuspend in more solution.
