Microorganisms such as bacteria import nutrient materials that are needed for their growth and survival from the environment as well as exporting metabolites. As the cytoplasm of microbes is separated from the environment by the hydrophobic plasma membrane which is impermeable to hydrophilic solutes, most of the hydrophilic compounds can only pass through the plasma membrane by means of integral membrane proteins which include carrier proteins, permeases or transporters due to the permeability barrier exerted by the phospholipid components of plasma membrane.
Movement of solutes in and out of bacteria can be classified by the following processes: diffusion, facilitated diffusion, osmosis, active transport, group translocation, endocytosis and exocytosis. As related to active transport and group translocation, energy is invested in active transport
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Active transport is a process in which both transport proteins and metabolic energy are utilized to transport solutes across the plasma membrane against the concentration gradient at different magnitude, allowing solutes to accumulate even when their concentration outside the cell is lower. There are a few characteristics of active transport which play significant role in solute transport whereby the carrier proteins possess solute specificity in enzyme-substrate relationship, energy is required to change the affinity of transport protein for transported solute at the other side of plasma membrane, accumulation of transported solutes against concentration gradient as well as remaining the solute structure unchanged during active transport. With the aid of active transport systems, microbes such as bacteria can grow efficiently in low nutrient concentration environment since nutrients can be accumulated within the cell with the expense of large amount of energy in the form of ATP or electrochemical