BACTERIOCHLOROPHYLL-C FORMATION AND CHLOROSOME DEVELOPMENT IN CHLOROFLEXUS-AURANTIACUS

The dependence of chlorosome development on bacteriochlorophyll (BChl) c synthesis was studied with the phototrophic green bacterium Chloroflexus aurantiacus. By selecting defined culture conditions, three possibilities could be identified. Upon addition of 5-aminolevulinic acid, cells of resting cultures increased their specific BChl c 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 BChl c 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 BChl c 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 BChl c without concomitant formation of chlorosomal polypeptides. This means that there was no obvious coordination of polypeptide and BChl c synthesis. On this basis, it appears unlikely that one of the chlorosomal polypeptides functions as an apoprotein of a presumed BChl. c holochrome complex.