Light as an energy source in continuous cultures of bacteriorhodopsin-containing halobacteria

Abstract

The role of light as an energy source for slightly aereated cultures of halobac­ teria was studied, using continuous cultures with low nutrient concentrations and a low oxygen supply. A series of experiments were carried out with non­ illuminated and differently illuminated cultures and with ditferent oxygen transfer rates. Under low oxygen availability, light proved to be a decisively important energy source that allowed the populations to reach higher growth rates and much higher population densities. Oxygen inftuenced the growth over only a minimal level, below which neither the illuminated nor the dark cultures were atfected by the oxygen transfer rate. From these results, it appears that the bacteriorhodop­ sin-mediated energy supply could have a very important role for the ecology of halobacteria in their microaerophilic habitats. In the illuminated cultures, cells that originated purple colonies on plates appeared. These cells, which could be bacteriorhodopsin-constitutive mutants, are now being studied.