A halorhodopsin-overproducing mutant isolated from an extremely haloalkaliphilic archaeon Natronomonas pharaonis

The halorhodopsin (hR)-overproducing mutant strain KM-1 was isolated from the extremely haloalkaliphilic archaeon Natronomonas pharaonis type strain DSM2160T. hR-enriched membranes were easily obtained by washing the cells with distilled water. The membranes were claret colored owing to two pigments: hR and bacterioruberin. The hR component in the absorption spectra changed from blue to purple upon the addition of Cl− and had a Km value of 1.7 mM. Overexpression of hR in strain KM-1 might be caused by the point mutation Asp324 → Asn in the bacteriorhodopsin activator homologues of N. pharaonis. The mutation changed the hR-expression pattern from inducible to constitutive in the late exponential phase.