Over-expression of the C82-methyltransferase BchQ in mutant strains of the green sulfur bacterium Chlorobaculum limnaeum for synthesis of C8-hyper-alkylated chlorosomal pigments

Abstract The pigment 8-isobutyl-12-ethyl-([,][I,E])bacteriochlorophyll (BChl) c is key to chlorosomal self-aggregation structures in vivo and was found to produce an organogel in carbon tetrachloride in vitro. Therefore, [I,E]BChl species have been the focus of both fundamental and applicational studies. Since these pigments are very rare in naturally occurring bacterial cells, a method was designed for large-scale production. Here, mutants over-expressing C82-methyltransferase BchQ were constructed using the wild-type and mutant stains of the green sulfur bacterium Chlorobaculum limnaeum. The C8-hyper-alkylated BChls c, d, e, and f, as well as [I,E]BChl species were synthesized by cultured cells. The results showed that more than 95 % of C8-hyper-alkylated BChl c and BChl d were successfully produced in bacterial cells. These findings should prove useful for further development of new chlorosomal models and antenna devices for artificial photosynthesis.