Abstract
Green sulfur bacteria usually contain only one kind of bacteriochlorophyll(=BChl)s c, d and e as chlorosomal pigment. However, we reported that two substrains containing exclusively 20-methylated BChl c and 20-unsubstituted BChl d, respectively, were isolated from Chlorobium (Chl.) vibrioforme NCIB 8327 (called C or D substrain, respectively). We also reported that Chl. vibrioforme DSM 263 possessed both BChls c and d. As these strains belong to the same clone, we investigated the activities of their Bchl c 20-methyltransferase and the gene bchU expression. Sequence analysis of bchU indicated that DSM 263 strain and the C substrain were derived from the D substrain by the reverse mutations in the inactivated bchU during relatively short-time cultivation. Relatively higher tolerance of the C substrain against oxygen than that of the D substrain would serve as a selective pressure toward reverse mutations of the inactivated bchU.