Production of pure photosynthetic cell biomass for environmental biosensors

The feasibility of producing pure photosynthetic cell biomass heterotrophic ally and activating their photosynthetic apparatus through light illuminati on was investigated using Chlorella sorokiniana and Euglena gracilis. Altho ugh the chlorophyll contents of Chlorella and especially Euglena cells decr eased during heterotrophic cultivation, photoactivation of the cells result ed in sharp increases in their chlorophyll and some other metabolites conte nts. Furthermore, the cells swiftly changed from heterotrophic to photoauto trophic metabolism and vice versa, when the culture conditions were cyclica lly changed from heterotrophic to photoautotrophic. Under this condition, t he cells grew continuously and, depending on the light condition during the photoautotrophic phase, there was a stable fluctuation in the intracellula r metabolites concentrations. In the case of Chlorella, for example, the pr otein content of the cells decreased during the heterotrophic phase and the n increased during the photoautotrophic phase. The results implied that the cells retained their photosynthetic apparatus during the heterotrophic cul tivation and can be easily activated by illuminating the culture. An internally illuminated photobioreactor, which can be used for both heter otrophic cultivation and photoactivation of the cells was therefore constru cted. Using this reactor, the cells are first cultivated heterotrophically to a high cell concentration and when the organic carbon source is complete ly exhausted, the reactor is illuminated for photoactivation of the cells. The photobioreactor has high mass transfer capacity (for efficient heterotr ophic culture) and high light supply capacity (for efficient photoactivatio n). It can be illuminated by both artificial and solar light, can be mainta ined under strict sterile condition and easy to be scaled up. (C) 2000 Else vier Science S.A. All rights reserved.