Pheophytinization of bacteriochlorophyll c and energy transfer in cells ofChlorobium tepidum

Bacteriochlorophyll (BChl) c in whole cells of Chlorobium tepidum grown at 46 degrees C changed into bacteriopheophytin (BPhe) c within 10 days after reaching full growth. When a small amount of C. tepidum cells in which BChl c had been completely pheophytinized were transferred to a new culture med ium. normal growth was observed after a short lag phase, and the absorption spectrum of the growing cells showed the presence of a normal amount of BC hl c. During the growth of C. tepidum in the new culture, the BChl c concen tration was nearly proportional to the cell density measured by turbidity ( OD640). These results indicate that C. tepidum? can survive even when BChl has been completely pheophytinized and that BChl c is newly synthesized in such cells when transfer-red to a new culture medium. In pal-try pheophytin ized cells, upon excitation of BPhe at 550 nm the fluorescence emission spe ctrum showed maxima at 775 and 810 nm, which correspond to emissions from B Chl c and BChl a. respectively. This indicates energy transfer from BPhe c to BChl c and BChl a. Ln cells in which BChl c was completely pheophytinize d, fluorescence measurements were indicative of direct energy transfer from BPhe c to baseplate BChl tr. These findings suggest that when BChl c in C. tepidum cells is pheophytinized, the product (BPhe c) remains in the chlor osomes and continues to work as a light-harvesting pigment.