Investigation of factors influencing oxygen content in Halobacterium salinarum growth medium for improved bacteriorhodopsin production

Abstract

Improving production of bacteriorhodopsin in the culture medium of Halobacterium salinarum confronts indeterminacy related to culture conditions. Several studies have revealed that high oxygen content increases the growth of Halobacterium salinarum whereas it down-regulates the expression of genes responsible for bacteriorhodopsin production. The focus of this study was to clarify this contradictory role of oxygen in bacteriorhodopsin production and to indirectly regulate the oxygen content of the culture medium at a level that would increase the final concentration of bacteriorhodopsin. Oxygen consumption evaluation showed tha in a typical growth of Halobacterium salinarum at aerobic condition, the decrease in oxygen demand was concurrent with a sharp increase in bacteriorhodopsin production. Further investigation on culture conditions revealed that agitation rate and filling volume had a linear correlation with the cell growth and bacteriorhodopsin production by each cell, however, a two-factor interaction model described the relationship between the culture condition and overall bacteriorhodopsin concentration. It was concluded that although each cell of Halobacterium salinarum produced high amount of bacteriorhodopsin at low turbulence condition, the low yield of biomass production at this condition caused a low overall bacteriorhodopsin concentration. The highest overall bacteriorhodopsin concentration was obtained from high turbulence condition, in which cell numbers were high enough to compensate for low production of bacteriorhodopsin by each cell.