Detection of bacterial aggregation by flow cytometry

Since the advent of recombinant DNA technology, bacteria have been used often to express foreign proteins [1]. Soluble proteins expressed by bacteria can be expressed either in the cytoplasm or they are secreted to the periplasm or outside the cell. In general proteins expressed in the cytoplasm are expressed to higher levels than if they are secreted[1]. Many hydrophobic and highly expressed proteins in the cytoplasm form inclusion bodies of aggregated protein that are difficult to solubilize [1]. Proteins targeted to the periplasm or outside of the cell often do not all get secreted and form insoluble aggregates [1, 2]. Different growth and induction conditions for the expressing bacteria can sometimes allow for soluble expression of a previously insoluble protein [2].