Bacterial rhodopsins of newly isolated halobacteria

SUMMARY: Several new halobacterial strains were isolated from crude solar salts commercially produced in Mexico and Australia. The presence of bacteriorhodopsin (BR)- and halorhodopsin (HR)-like pigment in their total membrane fraction was measured by flash spectroscopy and light-induced ion pumping activity. Two of these strains contained both BR- and HR-like pigments; the others contained only BR-like pigment. DNA hybridization analysis with probes from bacterioopsin and haloopsin genes revealed that the genes encoding the BR- and HR-like pigments were not homologous to those found in Halobacterium halobium R1. In addition, the presence of sensory rhodopsin (SR)- and phoborhodopsin (PR)-like pigment in these membranes was detected by flash spectroscopy. The kinetics of the cyclic photoreaction of the SR-like pigment was more than 15 times slower than that of H. halobium. A PR-like pigment existed in two strains, and the kinetics of the cyclic photoreaction of the PR-like pigment was similar to that found in H. halobium.