Investigation of bacteriochlorophyll biosynthesis genes in Blastochloris viridis by functional complementation of mutants of Rhodobacter capsulatus

Abstract

Blastochloris (formerly Rhodopseudomonas) viridis produces bacteriochlorophyll (BChl) b which is distinguished from BChl a by the possession of an ethylidene group at C8 instead of an ethyl. This chemical structure enables to BChl b to absorb longer wave length light (~1100 nm) than BChl a. To investigate genes involved in the BChl b biosynthesis, we have constructed genomic DNA libraries from B. viridis and introduced them to mutants of the nonsulfur purple bacterium Rhodobacter capsulatus which is deficient in BChl a biosynthesis. Total ten kinds of R. capsulatus mutants, three Mg-chelatase (BchD, H, I) mutants, three protochlorophyllide reductase (BchB, L, N) mutants, Mg-protoporphyrin IX methyltransferase (BchM) mutant, Mg-protoporphyrin IX monomethylester oxidative cyclase (BchE) mutant, bacteriochlorophyll synthase (Bch G) mutant, and 2-vinyl-bacteriochlorophyllide hydratase (BchF) mutant, were functionally complemented by B. viridis library DNA. The complemented R. capsulatus strains were demonstrated to be capable of synthesizing BChl a under photoautotrophic growth conditions.