Functional Complementation of Protochlorophyllide Reductase Activity in Mutants of Rhodobacter Capsulatus by Introduction of a Genomic Library from Green Nonsulfur Bacterium Chloroflexus Aurantiacus

Abstract

Green nonsulfur bacteria are a diverse group of photosynthetic bacteria that are particular of evolutionary significance. On the basis 16S rRNA sequence data, it was demonstrated that this group of photosynthetic bacteria forms a very deep division within the eubacterial line of descent (1). Its position as the deepest division of phototrophs suggests that its ancestors diverged earlier than did those of any other phototrophs. These bacteria contain bacteriochlorophyll c (Bchl c) in chlorosomes which are their major light-harvesting pigment complexes. The energy captured in the chlorosome is transferred to the reaction center which contains bacteriochlorophyll a (Bchl a). Despite the evolutionary significance of this group of organisms, many genes involved in the process of photosynthesis including Bchl synthesis of green nonsulfur bacteria are still unknown. To elucidate genes involved in Bchl synthesis, we constructed a cosmid library containing genomic DNA from green nonsulfur bacterium Chloroflexus aurantiacus and introduced it to Bchl biosynthesis deficient mutants of purple nosulfur bacterium Rhodobacter capsulatus. Under the phototrophic growth conditions, two kinds of protochlorophyllide reductase mutant (bchB− and bchN−) strains of R. capsulatus were rescued.