Methods for Studying Transport in Bacteria

Abstract

The major objective of this chapter is to outline some of the important techniques which have been developed for the study of transport systems in bacteria. The techniques described are discussed in detail with respect to the study of the lactose transport system of Escherichia coli. It now appears that this transport system can serve as a useful model for a number of active transport systems in both bacterial and animal cells. In such transport systems, a protein (the “carrier”) embedded within the membrane mediates the translocation and accumulation of substrate; substrate appears within the cell without chemical modifications. The driving force for the accumulation of substrate is represented by the electrical and chemical forces acting on certain specific cations. In bacterial cells, accumulation by such transport systems is coupled to proton movements (see discussions by Mitchell, 1963, and Harold, 1972), whereas in animal cells such active transport is associated with the movement of sodium ions (for review, see Schultz and Curran, 1970). In the absence of energy coupling, however, these systems catalyze the facilitated diffusion of substrate across the cell membrane.