[Blue-light-enhanced acid production of chlorella under anaerobiosis]

Under anaerobiosis the pH-value of the medium (0.002 M phosphate buffer) of a chlorophyll-free, carotenoid-containing mutant of Chlorella vulgaris (211-11h/20) drops slowly due to the excretion of acid fermentation end products. Blue light enhances this acidification of the medium (Figs. 1 and 2). Preliminary determinations of glycolic acid (color reaction with 2,7-dihydroxynaphthalene) indicate that there is about twice as much of this compound in the medium of an anaerobic culture kept in blue light as there is in the medium of one kept in the dark.Addition of oxygen after a period of anaerobiosis in darkness or in blue light results in a greater O2-uptake by the previously illuminated cells (Fig. 3), indicating aerobic consumption of the acids released under nitrogen. The latter is proven by the experiment shown in Fig. 4, in which parallel cell samples develop a greater O2-consumption when suspended in the isolated media (phosphate buffer) of anaerobic cultures of the same organism instead of in fresh phosphate buffer, and a greater O2-consumption when suspended in the medium of an illuminated rather than in that of a dark anaerobic culture.In experiments in which acid production is determined by measurement of the amount of 0.01 N NaOH required to keep the pH constant (Fig. 5), it can be shown that even traces of blue light can be effective in increasing the acidification of the medium of anaerobically kept cells; application of about 250 ergs cm(-2) sec(-1) of λ455 nm yields half-saturation (Fig. 6). Wavelengths around 470 and 370 nm are most effective in increasing this acid excretion; there is a minimum of activity around λ400 nm and no effect at all with yellow, red and far-red light (Fig. 7).From the similarity between these intensity and spectral dependences and those for a light stimulation in respiration of the same organism found earlier (KOWALLIK, 1967), and from the fact that the acids released into the medium under anaerobiosis can be respired by the algae, we feel that both these increases are based on the same light reaction. The action of blue light in bringing about an enhancement in respiration might then consist in furnishing additional substrate.