Ion Transport Coupled to Terminal Oxidase Functioning in the Extremely Alkaliphilic Halotolerant Bacterium Thioalkalivibrio

Abstract

Proton transport in the terminal part of the respiratory chain in the extremely alkaliphilic halotolerant bacterial strain Thioalkalivibrio versutus was studied under near-optimum growth conditions (pH 9.0-9.5). Under these conditions, bacterial cells generated electric potential with the negative charge being inside the cells. When only the terminal part of the respiratory chain functioned, it was found that: 1) unlike other bacteria known, this bacterium did not acidify the medium in the presence of K⁺ and valinomycin; 2) in the presence of an uncoupler, CCCP, but in the absence of valinomycin, reversible alkalinization of the medium occurred as a result of proton influx into the cells. Cyanide prevented this alkalinization. The difference spectra indicate that cell membranes contained cytochromes c and (b + o), some of which reacted with CO. The respiratory activity of membranes in the terminal part of the respiratory chain was optimal at pH 9.5 and specifically depended on sodium ions (C _1/2 = 10 mM). The data suggest the presence of a Na⁺-pump in the terminal part of the respiratory chain of the studied strain which can pump Na⁺ out of the cells.