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 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.