Bacteriochlorophyllc formation and chlorosome development inChloroflexus aurantiacus

The dependence of chlorosome development on bacteriochlorophyll (BChl)c synthesis was studied with the phototrophic green bacteriumChloroflexus aurantiacus. By selecting defined culture conditions, three possibilities could be identified. Upon addition of 5-aminolevulinic acid, cells of resting cultures increased their specific BChlc contents as well as the volumes of already existing chlorosomes. The number of chlorosomes, however, remained constant. Serine-limited chemostat cultures grown under steady state conditions exhibited constant rates of synthesis of both BChlc as well as of chlorosomes. The volume of the latter remained constant, as well. Upon addition of ALA to chemostat cultures, chlorosomes were synthesized at the same rate as before but their volumes increased as a consequence of increased BChlc incorporation. In chlorosomes isolated from resting cultures supplied with ALA the amounts of all of the polypeptides increased only slightly, if at all. Moreover, the ratio of all of the chlorosomal polypeptides remained largely constant. These results show that chlorosomes may incorporate newly synthesized BChlc without concomitant formation of chlorosomal polypeptides. This means that there was no obvious coordination of polypeptide and BChlc synthesis. On this basis, it appears unlikely that one of the chlorosomal polypeptides functions as an apoprotein of a presumed BChlc holochrome complex.