Physiology and Biochemistry
Acidophiles display a great range of adaptations to not just tolerating, but thriving in an extreme pH environment (the definition of an acidophile being an organism that has a pH optimum below pH 3). Principal in these is the necessity of maintaining a large pH gradient, to ensure a circumneutral cytoplasm (normally, however not in Picrophilus species). The archaeans have already been discussed above, and further information on their and bacterial adaptations are in basic form in the Figure. To elaborate upon the figure, the bacteria also use membrane proton blocking to maintain a high cytoplasmic pH, which is a passive system as even non-respiring A.ferrooxidans exhibit it. Acidophiles are also able to extrude protons against the pH gradient with unique transport proteins, a process more difficult for moderate- and hyper-thermophiles; a higher temperature causes cell membranes to become more permeable to protons, necessarily leading to increased H+ influx, in the absence of other membrane alterations.
Read more about this topic: Acidophiles In Acid Mine Drainage
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