Solute Transport, Microbial

Abstract

Abstract Solute transport systems in the cell and organelle membranes of industrial microbes play major roles in the physiological processes exploited for human benefit. Transmembrane transport of solutes is a major function of microbial cells, and commonly, some 15% of the total protein production of cells is devoted to transport proteins. Very often, the rates at which solutes enter cells determine the rates at which cytoplasmic enzymes can act on substrates from the environment. Transport systems are also important in the excretion of toxic materials from cells or in the production of exopolymers such as exoenzymes. Prominent types of transmembrane transport systems include channels, which mainly act as selective conduits for the movement of solutes, including water, through membranes and various carriers, which are commonly active, energy‐coupled transporters of solutes into or out of cells. These transporters may act by uniport, symport, or antiport, and also by group translocation, for example, in phosphoenolpyruvate:sugar phosphotransferase systems. Energy coupling for transport systems may be primary, for example, involving membrane F‐ATPases working in the synthase mode in conjunction with respiration or photosynthesis. Primary coupling can also involve cytoplasmic metabolism resulting in alkalinization of the cytoplasm, for example, through decarboxylation resulting in proton entry from the environment through F‐ATPases with net synthesis of ATP or energization of the cell membrane. F‐ATPases also play prominent roles in acid–base balance when they act in the hydrolytic mode to excrete protons when cells are in acid environments. Transport processes may also be secondarily energized by solute gradients across the cell membrane with, for example, antiport of the product of a metabolic process out of the cell with coupled antiport of the substrate for the process. Currently, there is an increasing appreciation for the roles of biofilms in industrial processes and the need to use biofilms, for which solute uptake may be diffusion limited, for the studies of transport processes of industrial microbes, which normally live in biofilm communities.