Illumination Effects on Bacteriorhodopsin Accumulation in Archaeon Halobacterium Halobium

Abstract

Highlights Effects of varying illumination conditions, including light intensity, light color, and illumination pattern on archaeon Halobacterium halobium growth and bacteriorhodopsin (BR) accumulation were first evaluated. LED green light was much more energy-efficient than the red and blue lights in this research. If energy consumption was not a concern, LED blue and red lights (or their combinations) were more effective for cell growth and BR accumulation, respectively, with a similar light intensity. Abstract. This study was to understand the effect of LED light intensity, color, and illumination pattern on the growth of and bacteriorhodopsin (BR) accumulation in archaeon Halobacterium halobium. Experimental results showed that archaeon growth and BR content increased with increasing white light intensity. Green and white LED lights were found to be the most effective for archaeon growth and BR accumulation; here, effectiveness is defined based on photons shined on the bioreactor. The 12-h light/12-h dark cycle illumination pattern resulted in longer lag phase but achieved higher final cell growth and BR accumulation than continuous white light or an instant flash of light/dark illumination. The fade pattern that had smooth transitioning among green, blue, and red lights was better than the jump pattern without transitioning. The highest cell dry weight and BR content of H. halobium were 1.84 g l-1 and 11.76 mg l-1, respectively, under 29.85 µmol/m2s LED white light illumination. The green LED light of 1.39 µmol/m2s had the highest energy-specific conversion effectiveness and saved energy consumption by 84 and 87% per cell biomass and BR dry weight, respectively, compared to the worst case of LED white light of 29.85 µmol/m2s. Keywords: Archaeon, Bacteriorhodopsin, Halobacterium halobium, Illumination pattern, LED light, Light color.