Stress on intracellular pH homeostasis

Adaptation time to an organic acid may be directly linked to the cell s ability to maintain its internal pH (pHj). The cell may be able to maintain its pH and also adapt to mildly acidic conditions but only for a short period. After this period the pH protection system fails and the cells become sensitive to the toxic effects of the acid. It is known that certain organic acids enter the cell much more easily than others and as a result more readily alter the pH of the cell. It may, therefore, be possible to explain the differences in adaptation times between acidulants by the varying abilities of organic acids to alter the pHj of the cell (Greenacre et al., 2003). 

In bacterial cells homeostasis is achieved by a combination of passive and active mechanisms (Hill, O Driscoll, and Booth, 1995). 

Passive homeostasis The very low permeability of the membrane to protons and other ions. This plays a major role in preventing large pH fluctuations, which follows variations in pH of the environment. Another factor in preventing serious disruption of the pH is the high buffering capacity of the cell, due to the protein content of the cytoplasm, as well as the presence of glutamate and polyamines. 

Active pH homeostasis Depends primarily on the potassium ion and the proton circuits. 

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