Bacteriorhodopsin (BR) in the purple membrane from halobacteria has recently been studied to apply the design of molecular electron device and optical computers
In this study, the effects of nutrient conditions and growth conditions on the production of bacteriorhodopsin (BR) by Halobacterium halobium R1 were examined. In order to increase the productivity, an internal membrane bioreactor system and an external membrane cell recycle system were employed.
In order to supplement amino acids to the medium, various complex nitrogen sources containing amino acids were examined in the flask culture. The yeast extract was found to be the best amino acids source. Among the elements of amino acids, argine, isoleucine, leucine, lysine, methionine and valine were found to be essential for growth. Six different cultures were provided by adding each of the six essential amino acids to the medium containing 5g/L of yeast extract, and the growth behavior of H. halobium R1 was observed. However, any difference in the growth rate was not observed.
The halobacteria are reported to utilize proteins and amino acids rather than carbohydrates, except glycerol. Experimental results showed that 0.1~1% glycerol stimulated the growth of cell as well as the production of bacteriorhodopsin.
The pH of the culture changed from 7 to 8 during growth. Through the study of the effect of initial pH on cell growth, the culture whose initial pH was 5 or 8 showed longer lag phase. The growth of H. halobium R1 and BR production were found to depend on the dissolved oxygen level rather than the pH value. The BR content of total protein was 1.25% under the aeration condition of 4~5 L air /min(2.7~3.3vvm), and 2.1% under the aeration condition of 2 L air/min(1.3 vvm).
In order to remove toxic product for the high cell density fermentation, an internal membrane bioreactor system and an external membrane cell recycle system were employed to obtain high cell density culture. As a result, productivity of 125 mg/L of BR was obtained from the internal membrane bioreactor system at a dilution rate of $0.066 hr^{-1}$, and that of 200~400 mg/L of BR from the external membrane cell recycle system at a dilution rate of $0.1 hr^{-1}$. The productivity achieved by the external membrane cell recycle system was 10~15 fold higher than that obtained by the corresponding batch cultivations.
