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 Chlorof lexus aurantiacus. By selecting defined culture conditions, three poss ibilities 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 ch lorosomes, however, remained constant, Serine-limited chemostat cultur es grown under steady state conditions exhibited constant rates of syn thesis of both BChl c as well as of chlorosomes. The volume of the lat ter remained constant, as well. Upon addition of ALA to chemostat cult ures, chlorosomes were synthesized at the same rate as before but thei r 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 l argely constant. These results show that chlorosomes may incorporate n ewly synthesized BChl c without concomitant formation of chlorosomal p olypeptides. This means that there was no obvious coordination of poly peptide and BChl c synthesis. On this basis, it appears unlikely that one of the chlorosomal polypeptides functions as an apoprotein of a pr esumed BChl. c holochrome complex.