Photoacclimation of Chlorella vulgaris to red light from light-emitting diodes leads to autospore release following each cellular division

The detailed light requirement for photosynthesis and photoautotrophic cell growth can be assessed using solid state technology. Advanced light-emitting diodes (LEDs), constructed with double-power double-heterostructure (DDH) gallium aluminum arsenide (GaAlAs) chips, were examined for their ability to support mass culture of the eucaryotic alga Chlorella vulgaris. LEDs with peak emittance of 680 nm (with half-power band width of 20 nm) were used as a sole light source for the cultivation of C. vulgaris. Fluorescent light (FL) served as a control. The final cell mass and specific cellular growth rate under LEDs were comparable to those obtained under full-spectrum light (FL). The narrow-spectrum monochromatic red light was found to reduce the average cell volume from 60 mu m(3) to 30 mu m(3), and to make the size distribution and the per cell DNA distribution narrower, but did not affect the total biomass production. By switching light sources, the two distinct cell population states (obtained under red LEDs and FL, respectively) were found to be interchangeable. Two parametric flow cytometric analyses showed that the cells grown under red LED light had a more uniform DNA content at all cell sizes, as compared to cells grown under FL. These results show that the critical cell size for releasing autospores under red LED is smaller than that under FL. The number of autospores in one mother cell when grown under LED light appeared to be two, so that the mother cells break up after only one round of DNA replication. Although the solid state LED light source altered the cell cycle behavior of C. vulgaris, it can be used as an effective light source for autotrophic growth. Use of LEDs therefore promises to advance the current state of algal photobioreactors due to their efficiency, smallness, reliability, long lifetime, and desirable light characteristics.