Some effects of light on the viability of rhodopsin-containing halobacteria.

Under starvation conditions, rhodopsin-containing halobacteria show a light-accelerated death under aerobic conditions. This is attributed to photooxidative processes. Under anaerobic conditions, halobacteria die rapidly in the dark, and light prevents death. Since it has been shown by others that lightdriven ATP synthesis can occur under anaerobic conditions, it is postulated that rhodopsin-mediated photophosphorylation is of survival value for this organism in the brines in which it lives, especially because the solubility of oxygen is low in highly saline waters and anaerobic conditions can often develop.