Toxicological study of biofuel ethanol with blue green alga Spirulina platensis

In this study, tolerance of the blue green algal strain Spirulina platensis (Spirulina) to biofuel ethanol was investigated by monitoring algal growth, measuring respiration, photosynthetic O2 production and chlorophyll fluorescence induction with varying ethanol concentrations. Algal growth monitoring showed a dose dependent inhibitory effect of ethanol. The concentration of ethanol which inhibits algal growth by 50% (IC50) was found to be 0.36 M. The rates of oxygenic photosynthesis and cellular respiration in a liquid suspension of S. platensis cells measured with a Clark-type oxygen electrode system revealed that ethanol affects both the photosynthetic apparatus and mitochondria. The ethanol IC50 value on Spirulina oxygenic photosynthesis was measured to be 1.59 M. The algal chlorophyll fluorescence induction indicated that ethanol at the IC50 concentrations of 0.36 M (with respect to algal growth) and 1.59 M (photosynthesis) can apparently uncouple certain antenna chlorophyll pigments from the photosynthetic reaction center systems, resulting in increased background chlorophyll fluorescence. In the presence of 1.59 M ethanol, the slow S to M fluorescence rise pattern appears altered, indicating that the photosynthetic excitation energy state 2 to state 1 transition in blue green algae is affected at such concentration. These results provide certain physiological insight of ethanol toxicological effects in S. platensis.