Аннотация:An extremely natronophilic archaeon, strain AHT32, representing a novel genus in the Halobacteriales, has been obtained from a hypersaline soda lake in south-western Siberia. The strain grew optimally in saturated soda brines at pH 10 with butyrate as a substrate. The cell suspension had orange-pink color that stimulated us for rhodopsin search. Due to the presence of carotenoids typical for the haloarchaea a presence of rhodopsin, however, was not easily detectable spectrometrically. In the presence of nicotine (an inhibitor of the retinal biosynthesis pathway [1]) the growth of AHT32 was depressed and the cell turned nearly colorless. Upon addition of all-trans-retinal to the nicotine-treated cells, fast spectral changes typical for the initial stage of rhodopsin regeneration were observed. However, the regeneration did not reach the formation of a purple pigment. This indicated the presence of an unknown aporhodopsin with the problem of mature pigment regeneration due to a damage either by prolong absent of retinal as a result of the nicotine treatment or by conditions inappropriate for the retinal incorporation. When the cells were illuminated by a green laser flash (t1/2 = 15 ns, [lyambda] = 532 nm [2]) to trigger a single photocycle of rhodopsin pigment, a decrease in the optical density at 570-580 nm (near the expected absorption maximum) and increase at 405-410 nm (common for the M-like intermediates) were observed. The results suggested the definite presence of a mass rhodopsin-like pigment with a typical photocycle in the investigated natronarchaeon. Registration of the electrical potential on the membrane of the AHT32 cells using tetraphenylphosphonium as a penetrating cation under temporal illumination of the suspension with fixed light allowed us to detect a light-dependent generation of electrical potential difference on the cell membranes which suggested an ion transport function of the found rhodopsin.