Effect of dissolved oxygen on Halobacteria salinarium and condensation of bacteriorhodopsin using aqueous two phase system

Abstract

Bacteriorhodopsin (BR) is a light-sensitive protein in the purple membrane (PM) of Halobacteria salinarium living in salty environments and is currently considered as a promising candidate material in the design of molecular electron device and optical computers. Recently, it has been researched vigorously cause of these potentials In this study, optimum fermentation condition of Halobacteria salinarium and efficient production of Bacteriorhodopsin (BR) were researched. First of all, screening of cells highly producing BR was carried with antibiotics such as Lovastatin and Novobiocin. In case of Lovastatin, $10^{-7}$ M was reported as optimum concentration. Cells with Lovastatin produced BR more than control at 2 folds, and yield was constant until $5^{th}$ succeeding culture at $10^{-7}$ M. In case of Novobiocin, there was no difference in yield. However, optimum concentration was shown from $0.078 x 10^{-6} M to 0.078 x 10^{-7}$ M. After cell screening, optimum fermentation condition was examined. In this study, relations of dissolved oxygen concentration to cell growth and BR synthesis were examined. As a result of flask culture, high aeration (250 rpm) was favorable to cell growth and low aeration (150 rpm) was favorable to BR synthesis. In case of Batch culture, relation of specific growth rate, $μ (h^{-1})$ and dissolve oxygen concentration, D.O. was examined. As a result, cells needed D.O. concentration over 0.005 mmol/L and cells highly produced BR at 0.05 mmol/L. Cells produced red membrane rather than purple membrane over 0.05 mmol/L. Also, optimum oxygen transfer condition was examined measuring $k_La$ and Oxygen Uptake Rate with dynamic method. $k_La$ and OUR were measured at $40 h^{-1]$ and 6.5 mmol/g dw-h in changing states of rpm and air flow rate. After setting optimum D.O. condition, efficient purification method of BR was examined with condensation methods such as aqueous two phase system and ammonium sulfate precipitation. After condensa...