==Mecanismos de acidificación citosólica==
Alkaliphiles maintain cytosolic acidification through both passive and active means. In passive acidification, it has been proposed that cell walls contain acidic [[ polymers]] composed of residues such as galacturonic acid, gluconic acid, glutamic acid, aspartic acid, and phosphoric acid. Together, these residues form an acidic matrix that helps protect the [[plasma membrane]] from alkaline conditions by preventing the entry of [[ hydroxide]] ions, and allowing for the uptake of [[ sodium]] and [[ hydronium ions]]. In addition, the [[ peptidoglycan]] in alkaliphilic '' B. subtilis'' has been observed to contain higher levels of hexosamines and [[ amino acids]] as compared to its [[ Neutrophile| neutrophilic]] counterpart. When alkaliphiles lose these acidic residues in the form of induced mutations, it has been shown that their ability to grow in alkaline conditions is severely hindered.<ref> HORIKOSHI, KOKI. "Alkaliphiles: Some Applications of Their Products for Biotechnology." MICROBIOLOGY AND MOLECULAR BIOLOGY REVIEWS 63.4 (1999): 735-50. Print.</ref>
However, it is generally agreed upon that passive methods of cytosolic acidification are not sufficient to maintain an internal pH 2-2 .3 levels below that of external pH; there must also be active forms of acidification. The most characterized method of active acidification is in the form of Na+/H+ [[antiporters]]. In this model, H+ ions are first extruded through the electron transport chain in respiring cells and to some extent through an [[ATPase]] in fermentative cells. This proton extrusion establishes a proton gradient that drives electrogenic antiporters—which drive intracellular Na+ out of the cell in exchange for a greater number of H+ ions, leading to the net accumulation of internal protons. This proton accumulation leads to a lowering of cytosolic pH. The extruded Na+ can be used for solute symport, which are necessary for cellular processes. It has been noted that Na+/H+ antiport is required for alkaliphilic growth, whereas either K+/H+ antiporters or Na+/H+ antiporters can be utilized by neutrophilic bacteria. If Na+/H+ antiporters are disabled through mutation or another means, the bacteria are rendered neutrophilic.<ref>Krulwich, Terry A., Mashahiro Ito, Ray Gilmour, and Arthur A. Guffanti. "Mechanisms of Cytoplasmic PH Regulation in Alkaliphilic Strains of Bacillus." Extremophiles 1 (1997): 163-69. Print.</ref><ref>Higashibata, Akira, Taketomo Fujiwara, and Yoshihiro Fukumori. "Studies on the Respiratory System in Alkaliphilic Bacillus; a Proposed New Respiratory System." Extremophiles 2 (1998): 83-92. Print.</ref> The sodium required for this antiport system is the reason some alkaliphiles can only grow in saline environments.
==Diferenzas na produción de ATP en alcalífilos==