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Detection of bacterial aggregation by flow cytometry

Jack Coleman1, Melis McHenry2
1Enzo Life Sciences, Farmingdale, New York, USA
2Beckman Coulter Inc., Miami FL, USA

Featured Product: PROTEOSTAT® Aggresome Detection Kit

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


The most common method of aggregate detection in a bacterial culture involves isolating the cells, disrupting them by sonication, separating soluble from insoluble proteins by centrifugation, and finally identifying the location of the protein of interest using polyacrylamide gel electrophoresis. A recently developed dye, PROTEOSTAT®, is now available that specifically stains amyloid type aggregates. The PROTEOSTAT® dye has been used to stain aggregates formed by overexpressed proteins in bacteria. In this application note, a simple and rapid method to identify aggregation in bacterial cells, showcased using a CytoFlex flow-cytometer, is described.

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