Review Article

Mechanisms of Metal Resistance and Homeostasis in Haloarchaea

Table 1

Various inorganic complexes formed in natural waters, seawater, estuarine waters (variable salinity), and hypersaline waters. As haloarchaea inhabit hypersaline environments where inorganic ligands predominate, inorganic metal speciation is described. The availability of metal depends upon the kind of inorganic complex formed. Lipophilic soluble chlorocomplexes of Hg and Ag are easily available in hypersaline waters. Insoluble (precipitated) ZnCl2 and CuCl2 are unavailable to the organism. Fe (II), Co (II), Ni (II), and Mn (II) form weak complexes with Cl that easily dissociate and can be taken up by organisms [28, 4146].

Metal Hypersaline
(5–35% salinity)
Sea water
(3.5% salinity)
Estuarine
(variable salinity)
River water/natural water

CdCdCl2, CdCl+CdCl+CdCl2, CdCl+Cd2+, CdCO3
AgAgCl0, AgCl2−,
,
AgCl0, AgHS0AgCl0, AgHS0,
AgCl2−, ,
Ag+, AgCl0
HgHgCl0, HgCl,
HgClHgCl0, HgCl,
Mixture of Hg- chloro and hydroxy complex
ZnZnCl2Zn2+, ZnCl2,
ZnCO3,
Zn(HCO3)2,
Zn(OH)2, ZnSO4
Zn2+, ZnCl2,
ZnCO3,
Zn(HCO3)2,
Zn(OH)2, ZnSO4
Hydrated Zn2+
CuCuCl2Carbonato and hydroxy complexesCuCl2, Carbonato and hydroxy complexesCu2+, CuCO3