Identification of Effectors: Precipitation of Supernatant Material

Bacterial secretion systems allow the transport of proteins, called effectors, as well as external machine components in the extracellular medium or directly into target cells. Comparison of the secretome, i.e., the proteins released in the culture medium, of wild-type and mutant cells provides information on the secretion profile. In addition, mass spectrometry analyses of the culture supernatant of bacteria grown in liquid culture under secreting conditions allow the identification of secretion systems substrates. Upon identification of the substrates, the secretion profile serves as a tool to test the functionality of secretion systems. Here, we present a classical method used to concentrate the culture supernatant, based on TCA precipitation.