The green sulfur photosynthetic bacterium Chlorobaculum tepidum newly produced BChl c derivatives possessing a chlorine or bromine atom at the terminus of the esterifying chain in the 17-propionate residue by cultivation with exogenous omega-halo-1-alkanols. The relative ratios of BChl c derivatives esterified with 8-chloro-1-octanol and omega-chloro-1-decanol were estimated to be 26.5% and 33.3% by cultivation with these omega-chloro-1-alkanols at the final concentrations of 300 and 150 mu M, respectively. In contrast, smaller amounts of unnatural BChls c esterified with w-bromo-1alkanols were biosynthesized than those esterified with omega-chloro-1-alkanols: the ratios of BChl c derivatives esterified with 8-bromo-1-octanol and 10-bromo-1-decanol were 11.3% and 12.2% at the concentrations of 300 and 150 jiM, respectively. These indicate that omega-chloro-1-allcanols can be incorporated into bacteriochlorophyllide c more than (abromo-1 -alkanols in the BChl c biosynthetic pathway. The homolog compositions of the novel BChl c derivatives possessing a halogen atom were analogous to those of coexisting natural BChl c esterified with farnesol. These results demonstrate unique properties of BChl c synthase, BchK, which can utilize unnatural substrates containing halogen in the BChl c biosynthesis of Cba. tepidum. (C) 2014, The Society for Biotechnology, Japan. All rights reserved.